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4-H Horse Program: Horse Science¹

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This educational material has been prepared for 4-H use by the Cooperative Extension Services of the U.S. Department of Agriculture and State Land-Grant Universities in cooperation with the National 4-H Council and the American Quarter Horse Association.

Trade or brand names used in the publications are used only for the purpose of educational information. The information given herein is supplied with the understanding that no discrimination is intended and no endorsement of products or breeds of horses by the Federal Extension Service or State Cooperative Extension Services is implied, nor does it imply approval of products or breeds of horses to the exclusion of others which may also be suitable.

This material is published by the National 4-H Council, 7100 Connecticut Avenue, Chevy Chase, Maryland 20815.

Programs and educational materials of National 4-H Council are available to all persons regardless of race, color, sex, age, religion, national origin or handicap. Council is an equal opportunity employer.

4-H HORSE PROGRAM HORSE SCIENCE

Since the time of ancient civilizations, the horse has served man well. He was first a war machine and that was his principal role until World War II. Likewise, the modern age has also relieved him of heavy duty as a beast of burden. But, the horse is not yet about to be turned out to pasture. He is now serving man in a greater way than ever before as a means of recreation and escape from pressure and tension of present-day living. This great versatility is possessed only by the horse because of his (1) anatomical structure and function, (2) speed and endurance, and (3) fear of being hurt. The combination of these characteristics has made it possible for man to obtain performance from the horse far beyond what is possible with any other animal.

ORIGIN OF THE HORSE

The horse had his beginning about 58 million years ago. His original home was in what is now the Great Plains area of North America. He evolved in three stages into his present form. The original ancestor (eohippus) was only about 12 inches high with four toes on each front foot and three toes each on each hind foot. He had a short neck, even teeth and was well-adapted to living in a forested and swampy environment. As the earth underwent geologic changes, the horse evolved into his second stage (mesohippus). Here he became larger (about 24" high), developed longer legs with only three toes on each foot. The middle toe was the largest. He also developed teeth suitable for grazing on the prairie and greater speed and endurance for finding forage and water and for protection and survival. These changes resulted from gradual adjustment to changing surroundings over millions of years.

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ARABIAN

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QUARTER HORSE

Fossil remains have definitely established that the horse originated in North America beginning with eohippus. There may have been an earlier five-toed ancestor but no fossil remains have so far been found.

The third and final stage in the evolution of the horse into his present form (equus) also took place in North America but this species completely died out for reasons yet unknown. Fortunately, some of the population escaped to Asia during the Ice Age (about one million years after eohippus) by way of what may have been a land bridge in the Bering Strait area between Alaska and Siberia. It was, therefore, in Asia and Europe that the horse completed his development and was domesticated. He did not return to North America until brought here by the Spaniards in the Sixteenth Century.

An important point is not how the horse developed into his present form but why. Besides having to go further in search of feed and water the horse also had to be able to run further and faster to escape his enemies. The horse is not the fastest animal on foot but possesses great endurance. The horse is, therefore, a creature of the open country and, to this day his first reaction to any strange or frightening object or situation is to panic and run away. This great fear of the unusual, plus the speed and endurance he has developed at the gallop, has made the horse a most valuable animal to man. But, it has also made him one of the most dangerous. Unlike a bull or lion, the horse seldom attacks directly. In an instant of fright, he can become completely unreliable and even pay no attention to his own safety. It might, therefore, be said that the modern horse must depend on man for his safety. The name eohippus or "dawn horse" is derived from the Greek word "eos" meaning dawn. The word horse comes from the Anglo-Saxon word "hors" meaning swiftness.

FUNCTIONAL DIVISIONS OF THE HORSE

The Head and Neck

The head and neck serve the same purpose on the horse as on other animal species. So far as behavior is concerned, the most important feature of this portion of the horse's physical make-up is the eye.

The eyes of the horse are rather large and are set wide apart the sides of the head. This gives the horse monocular vision or the ability to see separate objects with each eye at the same time. The horse can also see anything behind him that is not narrower than his body. The horse does not have binocular vision except when interested or excited enough to lift his head and point his ears forward. In such case, the object must be some distance away and not closer than four feet. Likewise, the horse cannot see directly downward and, therefore, can't see what he is eating. Neither can a high-headed horse see the ground directly in front of him.

The horse, because of his ability to make a quick getaway, has no need for acute vision as does man. However, his ability to see objects on either side at once, and to the rear, has been a prime feature of his ability to survive.

It is believed that horses do not all have perfect eyesight. No doubt, poor eyesight may have an effect on the behavior of certain horses. Shying at unfamiliar objects may be the result of faulty vision.

By reason of being ever alert to danger the horse, through his eyesight, is very sensitive to quick movements. Any training procedure involving quick motions, such as roping or polo must, therefore, be started slowly and speeded up only after the horse has become familiar with the motion.

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The Forehand Assembly

Although no one foot or leg has a single function, the front feet and legs serve primarily to support the horse at rest. In motion the front feet and legs also pull the horse forward. The horse's center of gravity is located at a point about six inches behind the elbow. At rest the front feet and legs, therefore, support 9 to 10 per cent more weight than the hind legs. The healthy horse at rest cannot shift his weight from one front foot to the other but is continually shifting weight between his hind feet. Only when one front foot is injured does the horse shift weight to the other foot. As a result, the healthy foot may go bad from lack of exercise necessary to promote circulation. To keep his feet healthy the horse must, therefore, have plenty of exercise. Stabled, or closely confined, horses often become nervous and this may well be due to their feet hurting from lack of exercise.

The horse is suspended between his front legs. The front legs are not attached to the main skeleton by any joints, but only held in position by muscular structures. This provides the horse with an almost perfect suspension system for his body. This, along with the elastic and expansive properties of the foot and the angle of the pastern joint, enables the horse to absorb and dissipate a tremendous amount of shock when in motion. For example, an 1100-pound horse carrying 200 pounds weight and running a quarter-mile in 45 seconds with a stride of 20 feet, will absorb and dissipate nearly a ton a second on his lead foot. In so doing, he leaves only a shallow footprint in the dust.

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FUNCTIONAL DIVISIONS OF THE HORSE

The Rearhand Assembly

This is the horse's powerhouse or propeller and serves to push the horse along in motion. The hind feet and legs also offer support at rest and catch weight at the end of flight in motion. Although the structure of the hind feet and legs is similar to that of the forelegs, less lameness and unsoundness occurs in the hind feet and legs because of their supporting less weight and doing less work. Proof of this is that the hind feet grow faster than the front feet.

While the horse's center of gravity is located about six inches behind the elbow, the center of motion, however, is located approximately over the 15th vertebra. This bony structure is the most upright member of the spinal column and on a mature horse about 10 inches back of the center of gravity. The horse in motion goes with these two centers in their relative positions. The position of the center of gravity, however, can be altered by the rider shifting his weight from side to side or front to rear. The horse himself can even shift the center of gravity by raising, lowering or extending his head. In contrast, the center of motion appears to be rather fixed. A rider's weight, positioned as nearly as possible over the center of motion, offers the greatest stability and interferes with motion the least. Weight too far back lessens the horse's propelling power.

The Power of Association

In the struggle to survive through the ages, the horse has learned to avoid or escape situations in which he might get hurt. He has, therefore, developed a great power of association. This is the basis of horse training.

To capitalize on the horse's power of association, signals or cues and punishment in training must be in proper sequence. For example,to teach a horse a particular movement or response, the appropriate signal must first be given and then followed immediately with some stronger force or punishment which will result in the horse responding in the desired manner. Once the horse has learned the lesson, the punishment must be stopped and not used again except as a necessary reminder. Reversing the sequence of signal and punishment will only confuse the horse.

Horses are born with a certain amount of intelligence which must be developed by training and good habits. What a horse knows he must be taught by man and, depending on training, this can either be good or bad.

The horse may shy at unfamiliar objects. He may also shy at familiar objects not in their usual place. Regardless, the horse must never be punished in such situations or due to his power of association he may develop the bad habit of shying at every strange object he sees. With his attention focused on the unfamiliar object the horse, if he can think at all, blames the object for the punishment. It is, therefore, better to let the horse study the object until he learns he will not get hurt and thereby gain confidence in the rider. This may be a rather new idea to many present-day horsemen, but the fact was observed by Xenophon, the Grecian soldier and scholar about 350 B.C.

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Since both conformation and action need to be included in light horse evaluation, the basic conformation features tending to affect action must be understood. The relationship of body parts to performance (form to function) will be here discussed with the body of the horse divided into four areas:

1. Head and Neck, 2. Fore Quarters, 3. Body or Trunk, 4. Rear Quarters.

HEAD AND NECK

The ideal head for each breed is described by the association publications. The descriptions all say the head should be broad in the forehead and between the eyes, short from the eyes to the nostrils and deep in the jaws. These words mean only that the head should be in proportion to the parts of the body of the horse. The proportion of the head tends to be an indication of body proportions. For example, a long narrow head indicates a long, shallow, narrow body.

Coarseness about the head indicates a coarse body, lacking quality. The ear should be medium size, attractively set and carried at a 45 degree angle to the axis of the head. Large, full, prominent eyes of a clear deep color are desired. Small blue eyes are considered weak. Small narrow, squinty eyes are often correlated with coarseness in quality and a lazy, sluggish, disposition.

Large nostrils allow for a maximum air intake and are of prime importance because the horse cannot force air into the lungs through the mouth as is possible in other species of animals. All breathing of air by the horse must be done through the nostrils.

All horses, both long and short necked ones, have seven cervical vertebrae. The shape of the neck is due largely to the amount and shape of the muscular tissues. The neck should be long, lean, and attached high up on shoulders with prominent withers. The lower part of the neck should be attached above the point of the shoulders. The throat latch should be cleancut and free from thick, meaty or fatty tissue to facilitate movement of the head at the poll and allow easy breathing.

Length of neck plays an important part in length of stride. Over the neck lie several layers of muscles, some of which control the movement of the scapula or shoulder blade, the arm, and indirectly the forearm. The muscles that control leg movements terminate at the knee. Cannon, pastern and foot action is controlled by ligaments and tendons. Larger neck muscles allow more muscle contraction extending the arm further and raising the forearm higher. This results in a longer stride. Another set of muscles extend from the front of the neck to the shoulder blade. Longer muscles here allow more shoulder blade movement and thus a longer stride.

A thick neck adds excess weight to the front end. This causes increased shock to the front legs because they ordinarily carry two-thirds of the body weight of the horse. A thick neck also decreases head movement giving slow, awkward turns.

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FORE QUARTERS

The withers should be prominent or high and well defined. They should extend rearward about one-quarter of the distance from the fore to the rear flanks. This is not possible unless the shoulder is long and has about a 45 degree slope. Such withers give the horse opportunity to have a long stride besides providing a good seat for the saddle.

The shoulder should be long, flat and smooth, with a 45 degree slope. This allows for increased shoulder movement which determines the arm movement and affects the stride. In a steep-shouldered horse the arm does not extend very far forward during movement. This decreases extension of the forearm and gives a short stride. Accordingly the slope of the shoulder increases length of the muscles and allows for more contraction and greater range of movement of the front leg.

The legs of the horse should be attached to the trunk to give the appearance of being on the four corners of the body. When viewed from the front, the cannons should descend from the center of the knees. Cannon bones should give the appearance of being flat when viewed from the side. This doesn't mean that the bones themselves are flat, but that splint bones and tendons and ligaments are set apart, well tied and give support at the posterior of the legs.

The front feet should be large, symmetrical and set at the same angle as the pastern. The foot should be especially wide at the heel and have considerable height at the heel as long as it is in keeping with the desired angle.

When viewed from the side the best combination of length for the various parts of the front quarter calls for a long shoulder, short arm, long forearm and short cannon. This gives a longer, more elastic stride and more speed.

A steep shoulder coupled with a long arm, short forearm and long cannon is the most undesirable shoulder and leg structure. This gives a severely shortened stride. Steep shoulders are usually associated with short, steep pasterns giving a hard, jolting ride because of decreased shock absorption.

A long sloping shoulder also forms a more desirable base for neck attachment giving a better balanced, more attractive horse.

TRUNK OR BODY

The trunk or body of the horse should be deep and broad. The back should be short and the loin wide and smooth. The back and loin together make up the top line which must be strong to protect internal organs, bear the weight of the rider and transmit to the front end the propulsion generated by the hind legs. The loin has no bone structure for support, making it the weakest part of the top line. The loin is a bridge between the rib cage and the hips. In order for the loin to perform its function of transmitting power from the rear to front end, it must be short and heavily muscled.

The back which must also be short and heavily muscled gets additional support from the rib cage. Often weak backs result from weak loins.

A short back and loin coupled with desirable shoulder and withers results in a long underline. However, a long underline does not insure a large body capacity unless it is combined with long, deep, well sprung ribs. This combination of short back and loin, long underline and long, deep, well sprung ribs insures ample capacity for breathing and consuming feed.

Length of underline also affects freedom of leg movement. A short underline can cause a horse to forge. This is striking the undersurface of the front foot with the toe of the rear foot.

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REAR QUARTERS

REAR QUARTERS

The croup or rump should be long, wide and level. This is the area from the loin to the tail head. Although the slope of the croup differs with light horse breeds, a level croup has longer muscles that enable a horse to take long strides and maintain speed for great distance. A more sloping croup sets the rear legs further under the horse so he may make a quicker start with the more powerful stride. Regardless of breed or slope to the croup, it should be long so the croup muscles can make maximum contraction. All muscles in the croup and thigh must be strong to supply the power from the rear quarters to propel the horse.

Adequate gaskin muscling is desired. The outer gaskin muscles help to pull the leg forward and enable propulsion, giving the horse a long, powerful stride.The powerful gaskin muscling also gives strength to the legs in turning and pivoting. The rear quarter is comparable to the forequarter in that a long croup, short thigh, long gaskin and short cannon gives the best stride.

Action

A long, straight, free elastic stride and coordinated, collected action is desirable. Excess lateral movement of the feet and legs reduces efficiency. Action is affected by the set of the feet and legs as well as by the anatomical characteristics already mentioned.

Fairly close hock action with the hind legs working beneath the body is essential.

EXAMPLES OF ANATOMICAL FEATURES RELATING FORM TO ACTION

1. A thick neck and filled throat latch gives a lack of flexion of the head and slow, awkward turns.

2. Horses with low, rounding withers or thick withers often hang low-headed in the bridle and handle front legs clumsily. They often forge.

3. Length and slope of shoulders tends to correspond to length and slope of pasterns. Properly sloped shoulders and pasterns (45 degrees) are related to a springy stride. Length of shoulders and pasterns is related to the length of stride.

4. Long forearms and gaskins are related to length of stride.

5. Horses standing straight on front feet are more apt to show straight stride and true action.

6. Short, straight shoulders give a short, straight stride with concussion.

7. If the front legs are set far out on the corners of the body, a rolling, laboring action in front will result. This condition often goes with thick withers and straight shoulders.

8. When points of the hocks turn slightly inward with points of the toes slightly outward and the rear cannons parallel, such a position of the rear legs is related to collected, rather than spraddled, action behind.

9. When points of the hocks turn outward, often a defect in action called limber hocks or rotating hocks occurs.

10. A calf-kneed position of the front legs gives a pounding gait and hard concussion of feet at completion of the stride.

11. A pigeon toed horse will paddle or wing out when he travels.

12. A splay-footed or toe-wide horse will dish or wing in when he moves.

13. A straight stilty angle of pasterns will give a stilty action and may give cocked ankles or other unsoundnesses such as sidebones.

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FOOT, HEEL, & TOE

Soundness in the horse is of extreme importance, since his efficiency in performance is dependent upon his ability to move. Any abnormal deviation in the structure or function of a horse constitutes an unsoundness. All unsoundnesses do not have the same degree of severity. Some unsoundnesses can be treated successfully, others can not. An example of a blemish is an unsightly scar or rope burn. A blemish does not interfere with the service ability of the horse.

Any time a horse is lame, we can suspect an unsoundness. Lameness is any irregularity in gait which results from moving with pain or difficulty. Lameness may be detected while the horse is in a standing position, however, it is most noticeable at the walk or trot. If lameness is severe, the horse will refuse to put weight on the affected limb, even in the standing position. When moving, the lame horse is forced to carry most of his weight on the sound limbs, hence the "nodding" of the head when the sound limb strikes the ground. When the lameness is on the left fore leg, the head will nod as the right foot is planted on the ground but will jerk up as the left or lame leg touches the ground. Lameness in both front legs is indicated by a stiff, stilted action and short stride. The head is carried higher than usual without nodding.

The exact location of lameness is often difficult to determine. Many common unsoundnesses of the legs may be detected by carefully comparing the opposite leg. Swelling and implantation can be observed by handling the leg.

Most unsoundnesses of the legs and feet are caused by injury, or excess stress and strain. Horses with faulty conformation are always subject to unsoundness. Many times it is possible to detect an unsoundness by being familiar with correct conformation. Concussion lameness is associated with straight backs and pasterns, for example.

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COMMON UNSOUNDNESSES AND BLEMISHES

The following unsoundnesses and lemishes are identified: U-soundness, B-blemish.

Head

1. Cataract (U) - cloudy or opaque appearance of the eye.

2. Defective eyes (U) - impaired vision or blindness.

3. Poll evil (U) - inflamed swelling of poll between ears.

4. Roman nose - faulty conformation.

5. Parrot mouth (U) - lower jaw is shorter than upper jaw.

6. Undershot jaw (U) - upper jaw is shorter than lower jaw.

Neck

1. Ewe-neck - faulty conformation.

Withers and Shoulders

1. Fistula of withers (U or B) - inflamed swelling of withers.

2. Sweeny (U) - atrophy or decrease in size of a single muscle or group of muscles, usually found in shoulder or hip.

Front Legs

1. Shoe boil or capped elbow (B) - soft, flabby swelling at the point of elbow.

2. Knee - sprung or buck knee - over on the knees. Faulty conformation.

3. Calf-kneed - back at the knees. Faulty conformation.

4. Splint (B) - capsule enlargement usually found inside upper part of front cannon.

5. Wind puff (U) - puffy swellings occurring either side of tendons above fetlock or knee.

6. Bowed tendons (U) - enlarged, stretched flexor tendons behind the cannon bones.

7. Ringbone (U) - bony growth on either or both sides of pastern.

8. Sidebone (U) - bony growth above and toward the rear quarter of hoofhead.

9. Quittor (U) - fistula of the hoofhead.

10. Quarter or sand crack (B) - vertical split in the wall of the hoof.

11. Navicular disease (U) - inflammation of small navicular bone usually inside front foot.

12. Founder (U) - turning up of hoof and rough, deep rings in hoof wall caused by over feeding, severe concussion or disease and abnormal management.

13. Contracted feet (B) - abnormal contraction of heel.

14. Thrush (B) - disease of the frog. such as sidebones. Fairly close hock action with the hind legs working beneath the body is essential.

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FOUNDERED HOOF

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A SIDEBONE

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SPLINTS

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CONTRACTED TENCCONS COCKED ANKLE OR KNUCKLING

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CAPPED HOCK

Body

1. Heaves (U) - difficult breathing, lung damage.

2. Roaring (U) - difficult breathing due to obstruction usually in larynx.

3. Rupture (U) - protrusion of internal organs through the wall (hernia) of the body. Umbilical or scrotal areas most common.

4. Sway back - faulty conformation.

5. Hipdown (U) - fracture of prominence of hip and falling away.

Rear Limbs

1. Stifled (U) - displaced patella of stifle joint.

2. Stringhalt (U) - nervous disorder characterized by excessive jerking of the hind leg.

3. Thoroughpin (U) - puffy swelling which appears on upper part of hock and in front of the large tendon.

4. Capped hock (B or U) - enlargement on point of hock. Depends on stage of development.

5. Bog spavin (U) - meaty, soft swelling occurring on inner front part of hock.

6. Bone spavin or jack spavin (U) - bony growth usually found on inside lower point of hock.

7. Curb (U) - hard swelling on back surface of rear cannon about four inches below point of hock.

8. Cocked ankle (U) - usually in hind feet, horse stands bent forward, due to contracted tendons.

9. Blood spavin (B) - swelling of vein usually below seat of bog spavin.

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SECTIONAL VIEW

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PERMANENT & TEMPORARY TOOTH

"How old is your horse, mister?" To such a 4-H question, the owner might answer full mouthed, smooth mouthed, he still has corner cups or I don't know as he isn't registered. Such answers tend to confuse the youngster of the motor age, nor can he readily find these answers too easily until he questions the grandfather age group.

General features of horses which indicate advanced ages are grey hairs around the eyes and muzzle, deep depressions above the eyes, slender and hardened muzzles and loose heavy lips with a longer “grin” than younger horses. But, these features are not accurate enough to estimate ages on younger horses. Since the horse is most useful to us from 3 to 15 years of age, we need more accurate methods for age determination during this period.

The teeth of horses under 12 years old can be most closely identified with their approximate age. In general, we must examine the incisor teeth for most accurate results. Of course, the registered horse has a recorded birth date, but many horses are not so fortunate. However, this technique is not foolproof as prolonged droughts, short grazing on sandy soils, cribbers, parrot mouths etc. all tend to make the horse appear different than his actual age. For instance, a horse at 7 years of age grazing in sandy country over a prolonged period might appear to be 8 or 9 by his teeth.

The technique of horse age determination is not new nor especially scientific as it has been passed down for many generations. The basics for determining the age of horses by their teeth are rather simple and is not an art only to be guarded by the horse trader or veterinarian. Age can best be estimated by examining the wear and slant of the incisor teeth.

1. Number and anatomy of teeth.

a) The foal of either sex has 12 molars or grinders and 12 incisors or front teeth for a total of 24 teeth.

b) The mature male horse has 24 molars or grinders and 12 incisors or biters plus 4 canine teeth or tushes for a total of 40 teeth.

c) However, the 4 canine teeth located in the interdental space between the incisors and molars erupt only in the gelding or stallion. These canine teeth in the mare are underdeveloped and seldom erupt above the surface of the gums thus giving the mare a tooth count of 36.

d) There are 6 incisors in each upper and lower jaw. There are 2 central incisors at the midline, 2 lateral incisors and 2 corner incisors in each jaw. The corners being closest to the interdental space.

e) Anatomy of teeth. By studying the longitudinal section of incisor teeth we can see how the tooth wears as age progresses.

2. Examining teeth.

Approach the horse gently from the left side and examine the teeth by parting the lips with the thumb and forefinger leaving the jaws closed. In examining groups of horses of mixed ownership ask the holder to part the lips. The angle of bit and size and color of teeth are noted first. For the next examination grab the tongue with the right hand and grab the lower lip with the left hand and the mouth will open for clear examination of the cups, wear etc.

3. General tooth eruption and development by ages. The temporary or milk teeth of the young horse are smallish and white with a distinct neck. The permanent teeth are much larger, stronger and have a darker color with distinct cups on the younger horse. *Inserts from “The Sound Horse”, Mich. Ext. Bull 330.

a) First period (birth to 2½ years).

1) 10 months. All milk teeth have erupted and in wear at 16-18 months.

2) 2-year-old. All milk teeth in wear.

b) Second period (2½ to 5 years).

1) 2½ years. Temporary centrals loosen and permanent centrals erupt. Age determination is most accurate from 2-5 years. Shedding of milk teeth and eruption of permanents may not occur.

2) 3½ to 4 years. Permanent laterals erupt.

3) 4½ to 5 years. Permanent corners erupt.

c) Third period (6 to 9 years).

1) 6 years. Age from here on is estimated mainly by the size, shape and disappearance of cups until

10-12 years of age. Cups disappear at rather regular intervals beginning with the lower centrals at 6 years.

2) 8 years. Cups have disappeared in the lower centrals and laterals.

d) Fourth period (aged).

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TEETH OF A TWO-YEAR AND THREE-YEAR OD COLT TEETH OF A FIVE-YEAR OLD HORSE

1) 10-12 years. After 9 years the accuracy of age determination becomes more difficult. At this age the angle of the bite slants more outward than the perpendicular bite noticed in younger horses. By 12 years, the cups have disappeared in the upper incisors and the horse has a “smooth mouth."

2) 15 years. The dental stars are smaller but more distinct and more centrally located.

3) 20-21 years. At this age teeth may become shorter, more triangular in shape on the wearing surface, have a noticeable spacing between adjacent incisors and the dental stars may become larger and occupy a central position on the wearing surface. Also, at this age, the bite is very slanting.

It is well to note that horses in this age group may appear to have much younger mouths if they have had excellent care with regard to lush grazing and grain feeding with accompanying good health throughout their life.

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TEETH OF A SEVEN-YEAR-OLD AND TWELEVE-YEAR-OLD HORSE. TEETH OF A FIFTEEN-YEAR-OLD HORSE

GLOSSARY

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TWENTY-ONE-YEAR OLD HORSE TEETH

Anatomy - The science of the structure of the animal body and the relation of its parts.

Angle of bite - The outer angle at which the upper and lower incisors meet.

Canine teeth - Teeth that appear in the interdental space on the male horse at 5 years of age. Sometimes referred to as tushes.

Centrals - The first centrally located upper and lower incisors.

Corners - The corner incisors or those located back and adjacent to the forward edge of the interdental space (third set of incisors).

Cribbers - A bad habit of some horses in which the animal grasps the manger or other object with the incisor teeth, arches the neck, makes peculiar movements with the head, and swallows quantities of air. Called also cribbiting and wind-sucking.

Crown of tooth - The top of a tooth protruding above the gum.

Cups - The hollow space on the wearing surface of the incisor.

Dental star - A star shaped or circle like structure near the center of the wearing surface of the permanent incisors.

Full mouth - When the horse has a complete set of permanent incisors.

Incisor - Slender teeth in front used for biting grass, feed, etc.

Interdental space - The gum space between the incisor teeth and molar teeth.

Laterals - The second set of incisors located between the centeral and croner incisors.

Longitudinal - Lengthwise. Parallel to the long part of the tooth.

Molars - Rear teeth or grinding teeth of the horse generally not used to determine age.

Neck of tooth - The part of the tooth between the crown and root located at the surface of the gums.

Parrot mouth - The upper incisors overhang the lower incisors and do not properly meet and therefore cause uneven wear.

Smooth mouth - Refers to the smooth biting surface of the upper and lower incisors after the cups have disappeared at 12 years of age or older.

Wear - Refers to the amount of use or wear observed on the biting surface of the incisors.

The birth of a foal is the end of a wondrous process. It starts with the merging of two tiny cells - one from the female animal (mare), one from the male (stallion). With the joining of these cells, a new animal is conceived.

The cell from the female is called an egg, or ovum. The cell from the male is a sperm. The egg and sperm are both sex cells, the very special cells that contain the genetic material an animal inherits from its parents. Two microscopic cells will completely determine the genetic makeup of the offspring. See the discussion of genes and chromosomes in the guide sheet entitled “How Inheritance Works in Horses”.

The production of sex cells is a unique and interesting process. Each of the two sexes has special organs to produce sex cells and carry out the process of reproduction. These are called the reproductive organs. Much of the reproductive process is regulated by secretions from the body's mature gland, the pituitary. A knowledge of many specialized terms are essential for you to properly understand and discuss this reproductive process.

Study This Specialized Glossary Before Proceeding

SPECIALIZED GLOSSARY

Accessory glands (ak-ses-o-ri). These glands are located along the urethra of the male. They produce fluids that nourish and preserve sperm.

Birth canal The birth canal includes the cervix and the vagina of the female. They are the organs through which the unborn animal passes at birth.

Cervix (sur viks). This is the narrow passage or doorway between the female's vagina and uterus.

Corpus luteum (kor pus lu te-um). A solid mass that forms in the follicle after the egg has left. It produces a hormone which helps maintain pregnancy. It prevents other follicles from developing while the unborn animal is growing in the uterus.

Epididymis (ep I-did I-mis). A mass of tubes connected to the testicle. Its main function is to store sperm.

Estrogenic Hormones Hormones that stimulate the development and maintenance of feminine sexual characters.

The principal estrogenic hormones are:

a) estradiol; b) estrone; c) estriol.

Estrus (es trus). The estrus period is commonly called “heat.”

Fetus (fe tus). The unborn animal as it develops in the uterus.

Follicle (fol I-k 1). A bubble-like structure on the ovary which contains an egg.

Follicle stimulating hormone (FSH). Comes from the pituitary and causes follicle growth.

Hormone (hor mon). A body-regulating chemical secreted by a gland into the blood stream.

Infundibulum (in fun-dib u-lum). The funnel-like membrane that surrounds the ovary. It catches the egg when it is released by the ovary.

Luteinizing hormone (LH). Comes from the pituitary and regulates corpus luteum in female and testosterone secretion in male.

Nucleus (nu kle-us). The dense center of a cell. It contains the genetic material.

Ovary (o va-ri). A female organ that produces eggs. There are two ovaries.

Oviduct (o vi-dukt). The tube which carries the egg from the ovary to the uterus.

Ovulation (o vu-la shun). The time when the follicle bursts and the egg is released.

Ovum (o vum). Scientific name for egg.

Placenta (pla-sen ta). The membrane by which the fetus is attached to the uterus. Nutrients from the mother pass into the placenta and then through the navel cord to the fetus.

When the animal is born, the placenta is expelled. It is commonly called the “afterbirth.”

Pituitary This gland located at the base of the brain secretes hormones which regulate the body.

Progesterone A steroid hormone secreted by the hypertrophied cells of the corpus luteum. It inhibits the action of estrogens. It aids in the development of the uterus for implantation and effective nutrition of the embryo.

Prolactin A hormone produced in the anterior pituitary gland. It initiates lactation or in the case of nursing mothers milk secretion is stimulated.

Sex cells The egg and the sperm. They transmit genetic material from the parents to the offspring.

Scrotum (skro tum). The sac-like pouch that suspends the testicles outside the male animal.

Sperm Male sex cells produced in the testicles.

Semen (se men). Sperm mixed with fluids from the accessory glands.

Testicle (tes ti-k 1). A male gland which produces sperm.

There are two testicles.

Urethra (u-re thra). The tube through which both semen and urine pass through the penis of the male.

Uterus (u ter-us). The muscular, spongy organ of the female where the unborn animal develops. It is commonly called the womb.

Vagina (va-ji na). The canal which leads from the uterus to outside the female. Sperm is deposited there by the male, and the fetus passes through the vagina at birth.

Vas deferens (vas def e-renz). The tube that carries sperm from the epididymis to the urethra in the male.

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MALE REPRODUCTIVE ORGANS

The primary sex organ of the stallion is the testicle. (There are 2 testicles.) The testicles produce sperm in the mature individual and also produce a hormone called testosterone. Testosterone regulates and maintains the male reproductive tract in its functional state. Testosterone is also responsible for the masculine appearance and behavior of the stallion. Each testicle contains a mass of minute, coiled tubules.

The inner walls or surface of these produce the sperm. The numerous thousands of minute tubules merge into a series of larger ducts which pass out of the testicle to a larger, coiled tube located adjacent to the testicle. This tube, the epididymis, is the place where sperm are stored while they mature. Sperm formation in the male is a fairly continuous process.

The testicles and epididymides are located in the scrotum which regulates the temperature of these structures. The scrotal temperature is several degrees cooler than that of the body cavity which is necessary for the normal development of sperm.

From the epididymis, the sperm move through a tube, the vas deferens, into the urethra. The urethra is the tube that carries urine from the bladder through the penis. The urethra also carries sperm from the junction with the vas deferens to the end of the penis.

Along the urethra are the accessory glands. Their names are the prostate, the seminal vesicles and cowpers gland. They produce fluids that nourish and preserve the sperm. During mating, the accessory glands discharge their fluids into the urethra. This washes the sperm forward through the penis. The combined fluid and sperm is called semen.

Puberty, or the capacity to produce sex cells, occurs in the stallion at the age of approximately one year. This is not a period of mature breeding capacity. Two-year-old stallions may be used for limited breeding service. Breeding use of the stallion should be deferred until after the age of two. Ask your veterinarian or an experienced horseman to explain care and management of the mature stallion to you.

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STALLION REPRODUCTIVE TRACT

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SPERM CELL

FEMALE REPRODUCTIVE ORGANS

The mare's reproductive organs are quite different from the stallion's. The female produces the ova or eggs, receives the sperm from the male, and provides a place for the unborn animal to develop.

The primary sex organ of the mare is the ovary. Each of the two ovaries is usually 2 to 3 inches long and somewhat bean-shaped. The other portion of the female reproductive tract is known as the duct system. It consists of the oviducts, the uterus, the cervix, and the vagina. The various parts of the duct system are connected together and attached internally to the upper body wall by a series of ligaments.

The ovaries produce the eggs. Each egg is contained in a bubble on an ovary. This bubble is called a follicle. There are hundreds of follicles on each ovary. At the same time by a process not completely understood, one or more follicles begin to grow while the others remain small. The follicle grows until it is about an inch in diameter. It is filled with a fluid. The egg is suspended in the fluid. Near the time of mating, a hormone causes the follicle to burst.

The fluid gushes out of the follicle, carrying the egg with it. The egg is then trapped in a very thin membrane that surrounds the ovary. Shaped like a funnel, this membrane is called the infundibulum. The infundibulum narrows into a tube called the oviduct. The oviduct carries the egg to the uterus, or womb. The largest of the female reproductive organs, the uterus is where the unborn young (the fetus) will develop.

The uterus has a thick wall with heavy layers of muscles. At birth, these muscles will contract with great pressure to force the new animal through the cervix and vagina (birth canal) and into the world. The lining of the uterus is soft and spongy, containing a vast network of blood vessels. This network of blood vessels provides a “bed” for the fertilized egg to settle into and develop.

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MARE REPRODUCTIVE TRACT

THE ESTROUS CYCLE AND FERTILIZATION

The estrous cycle of the mare may be divided into phases, i.e., diestrus (quiet period); proestrus (preparation); estrus (heat period). The average length of the estrous cycle for mares is 22 days but may vary from 17 to 30 days. Individual mares tend to retain their individual cycle characteristics with regard to length of cycle and length of estrous.

The mare is called polyestrus because she cycles continuously throughout the breeding season in the absence of conception. The mare is called seasonally polyestrus because there is seasonal fluctuation of the estrous cycle with regard to length, intensity and regularity. Most mares that exhibit no outward signs of estrus during winter months are said to be anestrous (without estrus) during that time. The estrous cycle may be irregular in the early spring. The most easily recognized phase of the estrous cycle is estrus (heat period) or the period of male receptivity. It is caused by the relatively large amount of a hormone, estrogen secreted during this state of rapid and maximum follicle growth. The average length of estrus is 6 days but often varies from 2 to 11 days. Periods usually decrease in length as the summer progresses. Ask your veterinarian or an experienced horseman to explain the external signs of estrus and for instructions on management of your mare during the breeding season.

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OVARY OF THE MARE

The period when a mare is out of estrus is generally called diestrus. This phase or stage usually varies from 10 to 18 days. The first part of diestrus involves corpus luteum development. In the absence of conception, the corpus luteum regresses within a few days and new follicle development once again takes place under the influence of a hormone (FSH) from the pituitary gland. The period of rapid follicle growth at the termination of diestrus is commonly referred to proestrus.

Many mares are capable of first reproduction at 4 years of age. Regular annual foaling is conducive to total life-time production. In most cases it is advisable to have mares examined for reproductive status prior to breeding. Policies regarding general sanitation, safety, and medical aspects should be observed in all equine breeding programs.

Fertilization is the process of the uniting of the sperm and the ova. The tubular or duct portion of the female reproductive tract undergoes rhythmic contractions during estrus and this activity is stimulated by mating at which time the sperm is deposited in the tract. This pulsating action plus the locomotion of the sperm in a fluid medium transport the sperm through the cervix and uterus into the oviducts. The sperm and the egg unite in the oviduct. Only one sperm fertilizes a single egg although several million sperm may be present in the reproductive tract of the female. Only one egg is usually present per conception in horses. Sometimes a mare will produce two eggs and if both are fertilized, twin embryos will start to develop. Identical twins result from a different situation. In this case a single egg divides into two independent cells or cell masses at a very early stage of development. Twin embryos are undesirable in horses because they are generally aborted prematurely.

The egg produced by the mare is small in size although it is much larger than a sperm. The egg has a nucleus which contains the genetic material. The sperm has a much different shape than the egg which is basically round. The sperm has a head, a middle section and a tail. The physical movement of the latter structure gives the sperm cell its property of locomotion in a fluid medium. The genetic material of the sperm cell is contained in the head section. Upon fertilization, a sperm penetrates the outside membrane of the egg and the head section is drawn into contact and union with the nucleus of the egg; thus the genetic composition of the new individual is established. Fertilization is also the stimulus for the egg to divide and grow to form the new individual. The fertilized egg usually undergoes its initial cleavages or divisions in the oviduct. Meanwhile, it is transported to the uterus where development progresses.

PREGNANCY AND BIRTH

Pregnancy is the time during which the fertilized egg develops in the uterus. This process is also known as gestation. For a period of about six weeks, the cell mass resulting from the fertilized egg grows as a “free floating” object in the uterus. During this time, the fetal membranes commence to form. Nourishment of the new individual during this early stage is provided for by uterine secretions. The hormone progesterone secreted by the corpus luteum assist in regulating the reproductive tract during pregnancy.

At approximately 6 weeks of pregnancy, the placenta attaches to the wall of the uterus and then provides for the nourishment of the fetus. Nutrients and oxygen are carried from the mare to the fetus and waste products from the fetus are eliminated through the placenta. The navel cord connects the fetus to the placenta.

The process of gestation in the mare requires about 340 days; however, it may vary from approximately 300 to more than 400 days following breeding. The fetus develops gradually although the most rapid period of growth takes place during the last 3 or 4 months of pregnancy.

Successful pregnancy ends in birth or parturition. At the proper time due to hormone action, the strong muscles of the uterus contract forcing the new animal through the birth canal and into the world. Until, now, the young animal received nutrients and oxygen from its mother's blood stream. But at birth the navel cord is broken. The animal must live on its own. Apparently the breaking of the navel cord stimulates the animal to breathe. This solves the problem of oxygen. As for nutrients, the mother's body has been preparing them for many weeks. The hormones produced during pregnancy have stimulated the milk glands. By the time of birth, they are ready to provide milk. Later, the mare will expel the remainder of the fluids and placenta to the completion of parturition. The entire process may require several hours.

Milk production and “letdown” is initiated by hormones secreted by the pituitary gland. The first milk or colostrum is seen just prior to or after parturition. Colostrum is very high in proteins and other nutrients which provide the foal with resistance to infections. It is very important to the new born foal that it receives the colostrum. The colostrum is exhausted and replaced gradually with normal milk by about two days after the initial nursing.

There will always be reproductive problems among horses but interferences may be minimized by good management practices. An understanding of some of the basic principles of the processes of reproduction can aid horse breeders materially in dealing with difficulties likely to be encountered.

Two tiny cells are the only links of inheritance an animal has with its parents. A sperm cell from the sire and an egg cell from the dam unite and grow into the new animal.

We know, therefore, that any characteristics inherited from the parents must come from these two cells. With good care and good nutrition, the material in the sperm and egg will determine almost everything about the developing animal - its size, its shape, its color, even is intelligence.

The study of how characteristics are passed from parents to offspring is the science of genetics. It's easy to see why genetics is important to horse breeders. In trying to understand the mysteries of inheritance, geneticists learn things which help to produce better horses.

GENES AND CHROMOSOMES

Inside the cells of animals are certain complex chemical compounds. These substances are the carriers of inheritance. They are called genes and chromosomes.

Chromosomes are long, thread-like structures made of complex protein. They can be seen with a microscope. In all body cells except the sperm and the egg, chromosomes exist in pairs.

Each cell contains a certain number of chromosome pairs, depending upon the animal. Man has 23 pairs of chromosomes in each of his cells. Here are the number of chromosome pairs for farm animals.

• • Horse 33

  • Cattle 30

  • Goats 30

  • Pigs 19

  • Sheep 27

  • Chickens 6

Strung along the chromosomes, somewhat like beads on a string are genes. Genes consist of complex molecules. They are chemically linked to the protein of the chromosome. Genes are too small to be seen with a microscope. But other research methods tell us they are there.

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NORMAL CELL DIVISION (MITOSIS)

Genes are the units of inheritance. Characteristics are passed from parents to offspring through genes. Genes are the "brains" of the cell. They determine what the cell will be like. This, in turn, determines what the body will be like.

Since chromosomes come in pairs, so do genes. Two genes exist side by side, each on one of the chromosomes in the pair. The total number of genes on a chromosome is not known, but they are many. And different chromosomes have different numbers of genes.

The unique thing about genes and chromosomes is that they are able to reproduce themselves.

As an animal grows, cells divide and form two. Before the cell divides, each chromosome duplicates itself. When the cell divides one of the duplicates moves into each of the two new cells. So the two new cells have exactly the same kind and number of chromosomes. This type of cell division is called mitosis.

CHROMOSOMES IN SEX CELLS

Genes and chromosomes act somewhat differently when sperm cells and egg cells are formed. In the testes of the male and in the ovaries of the female, cell division happens another way. The chromosome pairs separate, one member of each pair going to one new cell and the other member going to the other new cell. As these cells divide again, the single chromosomes form duplicates which go into each of the new cells. This makes the sperm or the egg contain only a single chromosome of each original pair of chromosomes. This type of division is called meiosis.

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SEX CELL DIVISION

In horses, the sperm from the stallion and the egg from the mare each contain 33 single chromosomes instead of 33 pairs. Because of the way chromosomes separate at meiosis, millions of different kinds of sex cells can be produced by one animal.

When fertilization occurs, the single chromosomes from the sperm join the single chromosomes in the egg. Once again pairs are formed. So the fertilized egg contains the same number of chromosome pairs as the cells of the parents.

This fertilized egg develops into a new individual, resembling each parent in some ways, yet different from them both. And probably different from any other individual in the world, since the slightest difference in gene make-up would make a difference in the animal.

Dominant and Recessive Genes

Most characteristics are determined by several pairs of genes. For this reason it is impossible to tell exactly what an unborn animal will look like.

A few characteristics, however, are determined by only one pair of genes. Black and red coat color in horses is one example.

By studying characteristics such as this, we can learn something about how inheritance works.

One pair of genes causes the coat to be either black or red, depending on which particular combination of the two genes is present. There is one gene for black and a corresponding gene (allele) for red. The horse will be black if he has two black genes or if he has one black gene and one red gene. This is because the black gene is dominant. The horse will be red only if he has two red genes.

Here's how the genes combine. Let the capital B represent the black gene. We use the capital because black is dominant. Let the small b represent the red gene. Since genes come in pairs, a horse could have two black genes (BB), one black and one red gene (Bb), or two red genes (bb). A black horse could have either BB or Bb genotype. (Genotype means genetic makeup.) A red horse would have bb genotype. The gene for red (b) is recessive to the dominant gene for black (B).

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Consider this problem: A red (chestnut) mare (bb) is bred to a truly black stallion (BB). What color will the foal be?

As the genes and chromosomes divide in the mare's ovaries, the bb genes separate. Each egg contains one b gene. Likewise, each sperm from the stallion contains one B gene.

When the sperm and egg unite, two genes influencing coat color are again present. The genotype of the foal will be Bb. Since the B gene for black dominates the b gene for red, the foal will be black.

His phenotype (outward appearance) will resemble the stallion. Both would be black. But their genotypes are different.

The foal is Bb and the stallion is BB. What then would happen if a black stallion that had a Bb genotype were bred to a red (bb) mare?

Two possible kinds of sperm would be produced by the Bb stallion. Half of the sperm would have the B gene and half would have the b gene.

It would be a 50:50 chance whether the B sperm or the b sperm united with the b egg from the mare. The genotype of the foal would be either Bb or bb. Thus half the foals from such a mating would be black and half would be red.

Suppose a Bb stallion were mated to a Bb mare. Both the mare and the stallion would be black, but both would carry a recessive gene (b) for red. Half the sperm would carry the B gene.

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Half the sperm would carry the b gene. The same would be true for the eggs.

Chances are 25 percent that the foal would have the BB genotype, 50 percent that it would have the Bb genotype, and 25 percent that it would carry the bb genotype.

Theoretically, of 100 such matings were made, 75 of the foals would be black. Twenty-five would be red. Of the 75 black foals only 25 would be truly black (BB) and 50 would carry a recessive red gene.

What would happen if a red (chestnut) stallion were bred to a red (chestnut) mare? In this case all the eggs and all the sperm would carry the b gene. All foals from such matings would be red. There are also several other pairs of genes that control other coat colors in horses. The many possible combinations of these genes cause the many different color patterns we see.

INHERITANCE OF SEX

We can use a similar analysis to show how the sex of a foal is determined.

In horses, there is one pair of chromosomes which does not exactly match. One is called the x chromosome and the other, the y chromosome. Stallions have one x and one y chromosome. Their sex genotype is xy. Mares have two x chromosomes. Their genotype is xx. (The small letters x and y do not indicate that either is dominant or recessive.)

In reduction division in the stallion, half the sperm contain an x chromosome and half contain a y chromosome. In the mare all egg cells contain x chromosomes.

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If a sperm carrying an x chromosome fertilizes the egg, the foal will have xx genotype. It would develop as a female. If a sperm carrying a y chromosome happens to fertilize the egg, the foal would be xy. It would be a stallion.

The chances are 50:50 for the foal to be male or female.

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COMPLICATIONS

So far we have seen how inheritance works in its simplest form. This basic system forms the pattern for all inheritance.

Complications arise where characteristics are influenced by more than one pair of genes.

Most of the important traits in horses, such as conformation, temperament, physical performance, size, muscularity, and longevity, are influenced by many genes. With 33 pairs of chromosomes and hundreds of genes involved, it is impossible to know a horse’s complete genotype.

Furthermore, all gene pairs do not work as completely dominant and recessive. We see this in certain kinds of flowers.

When the red flowering plants pollinate a white flowering plant, the flowers on the new plant are pink instead or red or white. In horses, the palomino color pattern is similar to this.

Finally, many things besides the genetic make-up affect a horse. He may have the genes for running fast, but unless he is fed properly, well-trained, and protected from injuries he may never win a race.

A horse with genes for just average temperament that is properly cared for may have a better disposition than one with good genes that is treated badly.

Much remains to be learned about inheritance in horses. The present-day popularity of horses should provide the incentive for further scientific study in this field.

The digestive system of the horse is different from that of the other farm animals. Although the horse has a single compartment stomach like man, the pig, and the dog, the horse can utilize roughages like the cow which is a ruminant.

This is possible because the horse has a special type of intestine.

The digestive system is composed of the alimentary canal and its accessory organs. The alimentary canal is a hollow tube which extends from the mouth to the anus and has the following parts: mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. Teeth, tongue, salivary glands, liver, and pancreas are the accessory organs.

Digestion is the process of preparation of food for absorption from the alimentary canal into the blood stream and elimination of the unabsorbed residue from the body. The digestive process includes the combined effects of mechanical, secretory, chemical, and microbiological factors. The mechanical factors are chewing (mastication), swallowing (deglutition), movements of stomach and intestines, and elimination of residue (defecation). The digestive glands secrete digestive juices. Bacteria and possibly protozoa are the microbial influences. Understanding the structure (anatomy) and function (physiology) of the unusual digestive system of your horse helps you appreciate proper feeding of your horse.

MOUTH

The mouth is the first part of the tract, and the first act of digestion is grasping of food (prehension) to convey it into the mouth. The horse’s upper lip is the main structure in grasping food because it is sensitive, strong, and mobile. In grazing the action of the lip places the grass between the front (incisor) teeth which cut the grass off. In manger feeding, the loose food is collected by the lip with the aid of the tongue. Water and milk are drawn into the mouth by suction caused by a negative pressure in the mouth created largely by the action of the tongue.

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Mastication (chewing) is the mechanical reduction of food into finely divided particles which provide a greater surface area for the action of digestive juices. Mastication also mixes the food with saliva which moistens the food thus facilitating chewing and swallowing. This is especially helpful with dry foods such as hays. Saliva is a secretion from 3 sets of paired glands (parotid, submaxillary, and sublingual) and other small glands found in the mouth.

Water makes up 99% of the horse's saliva with the other 1% composed of inorganic salts (ions), and proteins. There are no enzymes in the saliva of the horse. The secretion of saliva in the horse is stimulated by the scratching (mechanical action) of food on the mucous membrane of the inner cheeks. It has been estimated that a horse will secrete about 10 gallons of saliva in 24 hours. Hay will absorb 4 times its weight of saliva while oats will absorb about its own weight: 6 lbs. hay + saliva = 30 lbs.; 6 lbs. oats + saliva = 12 lbs.

The horse is well equipped for chewing tough, coarse feeds with a set of 40 upper and lower teeth in the male: 12 incisors or front, 4 canines, and 24 premolars and molars or cheek teeth. Mares have 36 teeth since they usually do not have canine teeth which in the male are located in the space between the incisors and premolars. Jaw movement is vertical (up and down) and lateral (side to side). Because of this, the upper jaw is wider than the lower; therefore, mastication can occur on only one side of the mouth at a lower teeth and on the outside of the upper teeth because of time. The cheek teeth wear sharp edges on the inside of the the lateral movement. These sharp edges cause damage to the tongue and cheek resulting in the horse eating slowly and wasting feed. Floating the teeth will remove these sharp edges. An annual check-up will prevent this and other dental problems. The lower incisors serve another useful function - the detection of age. (see section 4)

The horse is a relatively slow eater and chews food thoroughly requiring 15-20 minutes to eat a pound of hay and 5-10 minutes to eat a pound of grain. Deglutition (swallowing) is the complex act, involving a number of muscles and nerves, of conveying food from the mouth through the pharynx and esophagus to the stomach.

PHARYNX

The pharynx is a 6-inch muscular, funnel-shaped sac belonging to the digestive and respiratory tracts whose passages cross in this region. Food must move through the pharynx quickly so that it will not enter the larynx (windpipe) or be forced into the nasal passages. Once food and water enter the pharynx, it cannot return to the mouth due to the blocking action of the soft palate. Horses for this same reason cannot breathe through the mouth.

ESOPHAGUS

The esophagus is a muscular tube about 50 to 60 inches in length which extends from the pharynx down the left side of the neck to the stomach. Solid and semisolid food moves down the esophagus by wave-like contractions (peristalsis), while liquids are squirted down. These movements can be seen by observing a horse eating and drinking. Choke can occur in horses when food, especially dry grain, and other materials become lodged in the esophagus. Food and water will be observed returning through the nostrils. Peristalsis is a one-way action in the horse from the pharynx to the stomach; because of this, it is very difficult for the horse to vomit. The act of vomiting usually results in the rupture of the stomach or pneumonia from the vomited material being forced into the larynx then to the lungs.

STOMACH

The opening of the esophagus into the stomach, the cardia, is closed by a powerful involuntary ring-like muscle (sphincter). This also reduces the occurrence of vomiting since it is very difficult for material to pass from the stomach back into the esophagus. The horse has the smallest stomach compared with other farm animals. With only a capacity of 8 to 17 quarts, the horse should be fed portions of the daily ration 2 or 3 times daily rather than one large feeding.

Several types of glands and specialized cells are found in the stomach walls. Gastric juice and mucous secretions are produced by these specialized glands and cells. Gastric juice contains hydrochloric acid (HCl) and two enzymes, pepsin and gastric lipase. Pepsin is the enzyme which helps digest proteins. Gastric lipase helps digest fats into constituent fatty acids and glycerol; however, fat digestion is mainly by pancreatic lipase in the small intestine.

Hydrochloric acid (HCl) activates pepsin and cooperates with pepsin in the breakdown of protein. The rate of secretion of gastric juices is a continuous process with the rate increasing when food is eaten.

In the horse's stomach food has a tendency to arrange itself in layers. The first food passes into the bottom region first food to form layers. The partially digested food does of the stomach with subsequent food lying on or around the not leave the stomach until it has reached two-thirds of its capacity. Excess food consumed beyond the capacity of the stomach along with partially digested food pass on into the intestine. The emptying of the stomach is a continuous process during digestion. It requires a 24 hour fast to completely empty a horse's stomach. Stomach movement due to muscular contraction mixes the food with gastric juices and passes the ingesta into the duodenum.

When to water a horse has always been an important question. It has long been recommended never to water a horse during or immediately following eating because the water will wash food out of the stomach. This is not true.

Drinking during or following a meal has no harmful effect on digestion since most of the water passes directly from the esophageal opening to the intestine opening which are located quite close together due to the U-shaped form of the stomach.

Horses are prone to digestive disorders originating in the stomach. Feeding ground grains which are easily packed into a doughy mass, sudden changes in feeding, failure to reduce the grain ration during idle periods, and ingestion of excessive amounts of water are a few causes of stomach disorders.

SMALL INTESTINE

The small intestine is 70 feet in length and 3 to 4 inches in diameter; it extends from the stomach to the large intestine; it has three parts - the duodenum, jejunum, and ileum. The capacity of the small intestine is 48 quarts. The material leaving the stomach and entering the small intestine is known as chyme, and it is a fluid or semi-fluid. Two main types of factors influencing digestion in the small intestine are movements of the intestinal wall and secretions from the pancreas (pancreatic juice), the liver (bile), and the intestinal glands (intestinal juice).

The pancreatic juice is produced by the pancreas gland and contains several enzymes. Trypsin (activated trypsinogen) converts proteins and partly hydrolyzed proteins into peptides and amino acids. Pancreatic lipase hydrolyzes fats to fatty acids and glycerol, and pancreatic amylase which breaks down starch to maltose. Bile, a secretion from the liver, activates pancreatic lipase, assists in fat emulsification, and aids in absorption of fatty acids.

The bile duct and pancreatic duct empty into the 3 to 4 feet long duodenum about 5 to 6 inch from the pylorus, the stomach opening into the intestine. In other farm animals, bile is temporarily stored in a gallbladder. The horse does not have a gallbladder; there is a direct secretion of bile into the small intestine from the liver. Simple tubular glands are found throughout the small and large intestine which secrete the sugar digesting enzymes - maltase, sucrase, and lactase. Each of these enzymes attacks the individual sugar with the name similar to its own (maltose, sucrose, and lactose). The enzyme breaks the sugar into glucose which can be absorbed. These simple tubular glands also secrete a lipase similar to pancreatic lipase.

Absorption of many nutrients (Amino acids, sugars, fatty acids, minerals, and vitamins) occurs in the small intestine which is well equipped with small projections called villi. Villi increase the surface area which enhances absorption. Intestinal movements mix the ingesta with the digestive secretions, enhance absorption, move the material through the intestines, expel the residues, and assist in the flow of blood and lymph through the vessels of the intestinal wall. The great length of the small intestine leads to many problems such as twisted or telescoped intestine.

LARGE INTESTINE

Material which is not or cannot be digested in the small intestine passes into the large intestine which is divided into the cecum, large colon, small colon, rectum, and terminates at the anus. The important digestive action of the cecum and colon is due to the presence of bacteria and possibly protozoa (one celled animals) which (1) digest cellulose, the fibrous part of roughages, and other carbohydrates such as starch and sugars to produce energy yielding volatile fatty acids; (2) synthesize B-vitamins; and (3) synthesize amino acids. Absorption of volatile fatty acids apparently occurs in the colon.

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THE INTESTINAL TRACT OF THE HORSE

B vitamins are definitely synthesized by the bacteria of the large intestine; however, in certain situations the absorption of most of them may not be adequate to meet the need of the horse. On normal diets, B vitamin deficiency does not occur in the horse so adequate quantities of B vitamins are available either (1) in the feed (diet) or (2) by bacterial synthesis.

CECUM. The cecum, blind gut, lies between the small intestine and large colon. Its average length is 4 feet with a capacity of 28 to 32 quarts. It extends into the right flank. The presence of food in the stomach causes an emptying of the cecum into the large colon. Because of the microorganism digestive action in the cecum, it is a functional appendix.

LARGE COLON. The large colon with a diameter of 8 to 10 inches is 10 to 12 feet long and has a capacity of 80 quarts. The large colon extends from the cecum to the small colon where it terminates in a funnel shaped restriction. Because it is usually expanded with food, impactions may occur. Impactions occur also in the cecum and small colon.

SMALL COLON. The small colon extends from the large colon to the rectum. It is from 10 to 12 feet in length with a diameter of 3 to 4 inches. Water is reabsorbed from the contents of the small colon and the characteristic balls of feces are formed. Feces is the waste matter of digestion and contains water, indigestible and undigested food residues, cells sloughed off of the intestinal wall, and remains of digestive secretions.

RECTUM. The rectum extends 1 foot in length from thesmall colon to the terminal part of the digestive tract, the anus. A horse normally voids 33 to 50 lbs. of feces per day. Vigorous horses defecate 5 to 12 times daily.

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CECUM OF HORSE, LEFT VIEW

You probably feed your 4-H horse a supplement. You know that the supplement will make your colt grow faster and be healthier. The horse will be in “better shape” than if you just let him graze.

You know this because you know something about animal nutrition. Animals need many different kinds of nutrients. Different animals need different kinds and amounts of nutrients. This is where the science of animal nutrition comes in. Part of the animal nutritionist's job is to find out what nutrients animals need.

In feeding experiments, different feed ingredients are tried. In the laboratory, feeds are analyzed. Nutritionists search for the best combination of feeds for the kind of horse being fed. For mares nursing foals, the feed must help produce milk. For a pregnant mare, the feed is designed to help produce a healthy foal. For a young horse, feed is designed for growth and development as well as maintenance and energy.

After experiments are conducted, they are checked and rechecked. Then the results are used to make recommendations to horse owners. This means good rations for a minimum cost to horse owners. It also assures you that your horse is fed in a way to meet the needs of his body in the type of work that he is doing.

KIND OF NUTRIENTS

There are many different chemicals in feeds. Animals need some of them in large amounts - others are needed only in tiny amounts. Some have not been discovered or named yet.

These feed constituents are divided into five main types of nutrients. Each type has a different job in the animal's body. The five types are (1) energy nutrients (carbohydrates and fats), (2) proteins, (3) vitamins, (4) minerals, and (5) water.

None of these is more important than the others. All are essential. But with the exception of water, the energy nutrients usually make up the greatest bulk of feed. Energy nutrients are the body's fuel. In fact, they are even chemically similar to fuels we use - gasoline, oil and coal.

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After digestion, the energy nutrients are carried by the blood to the cells of the body. In reactions very much like burning, they are used by the cells for energy. Energy or fuel is required to power the movements of muscles - walking, a beating heart, breathing, blinking eyes and contractions of the digestive system. At the same time, heat is produced to maintain body warmth.

The main energy nutrient is carbohydrate. There are many carbohydrates. Even the relatively simple ones are complex compounds. All carbohydrates are made up of carbon, hydrogen and oxygen. Carbon is the key to carbohydrates. This element can behave in several different ways. As a result, there are thousands of possible combinations of carbon, hydrogen and oxygen.

Sugars and starches are carbohydrates. They are relatively simple. Cellulose is one of the more complex carbohydrates.

The sugars and starch are easy to digest. They have a high “feeding value” because very little of them pass through the body undigested. Grains such as corn and oats contain much sugar and starch.

Cellulose is chemically a carbohydrate. It makes up the fiber in plants. Grass has much cellulose. Cellulose is hard to digest. For most animals it has a low feeding value; however, ruminants (cattle and sheep) can digest large amounts of cellulose with the aid of bacteria in the rumen.

The caecum or large intestine of the horse functions similar to the rumen in cattle and sheep.

Another group of energy nutrients is the fats and oils. Fats and oils are chemically alike. Their main difference is that fats are solid at body temperature; oils are liquid. Both are usually called fats. Like carbohydrates, fats are made up of carbon, hydrogen and oxygen. They are also used to provide energy for movement and heat. Fats contain a higher percentage of carbon and hydrogen atoms than carbohydrates do. Thus, the energy in fats is more concentrated. Fat has 2.25 times more energy per gram than carbohydrate.

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THE PROTEINS

While carbohydrates and fats supply energy, proteins supply the material from which body tissue is made. They are the bricks and mortar from which bodies are built.

Proteins are highly complex. In addition to carbon, hydrogen and oxygen, they contain nitrogen. Some proteins also contain sulfur. A few contain phosphorus or iron. Like carbon, nitrogen can be combined with other chemical elements in different ways. The various combinations result in many different proteins. Each protein is made up of several nitrogen compounds called amino acids. These amino acids are the “building blocks” from which proteins are made. The chemical arrangement of the amino acids determine the quality of the protein.

During digestion, proteins are broken down into amino acids. These are absorbed from the intestine into the blood stream and carried to all parts of the body. Then they are recombined to form body tissue. Proteins that are eaten eventually become muscle, internal organs, bone and blood. Skin, hair, hooves, and many other parts of the body are also made of protein. If an excess of protein is fed, the nitrogen portion of the protein can be separated from the rest of the nutrient and be discarded in the urine. The remaining materials can then be converted into energy by the animal. TWO PROTEINS ARE NOT ALWAYS ALIKE IF MADE OF THE SAME AMINO ACIDS!

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THE VITAMINS

Although animals need large amounts of both energy and proteins, other nutrients are just as vital, but are needed in much smaller amounts. The vitamins are such a group.

For a long time, people noticed that certain diseases were caused by the lack of certain foods. Then modern science began analyzing the foods. They were found to contain small amounts of certain complex chemicals. Other foods did not contain them.

These nutrients were called vitamins, or “vital amines”. They are essential to normal body functioning. The vitamins are not chemically alike. Each one also has a different job in the body. Still, they are all classed together under the term vitamins. This is because they are all organic compounds. (They contain carbon). Also, all of them are needed only in very small amounts.

Vitamin A is responsible for the health of the eye and the tissue of nasal passages, lungs and digestive system. Vitamin D is responsible for the strength and proper development of bones and the mineral balance in the blood. Other vitamins have just as important functions.

Some animals require only certain vitamins in their feed, whereas others can manufacture some of their own. Feeds are a good source of certain vitamins. Carotene in green grass is a good source of vitamin A. Sunshine and suncured hay are good sources of vitamin D.

THE MINERALS

Like vitamins, minerals are usually needed only in small amounts. Unlike vitamins, they are inorganic - they do not contain carbon. Iron, copper, phosphorus, calcium, and magnesium are examples of minerals.

Minerals are important in the chemical reactions of the body. Without them, many life processes could not take place. Without iron in the blood, for instance, oxygen could not be carried to the body's cells. For animals such as horses that are very active, the oxygen carrying capacity of the blood is a very vital factor in their daily life. A race horse uses tremendous quantities of oxygen during a race.

Without calcium and phosphorus proper bone and tooth formation would not take place. These are examples of the need for minerals.

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WATER AS A NUTRIENT

The last item on our list of nutrients is so common that we seldom think of it as a nutrient. But water is the largest single part of nearly all living things. The body of a colt is three-fourths water, while an adult is approximately 50 percent water.

Water performs many tasks in the body. It makes up most of the blood, which carries nutrients to the cells and carries waste products away. Water is necessary in most of the body's chemical reactions. In addition, water is the body's built-in cooling system. It regulates body heat. It acts as a lubricant.

Life on earth would not be possible without water. An animal can live longer without food than without water.

FINDING OUT WHAT'S IN FEEDS

Research has provided the information that is available about the different kinds of nutrients. The scientist has developed methods by which the amount of each nutrient in a feed can be accurately determined. Knowing the nutrient content of a feed is very important to livestock raisers.

Water is one of the nutrients that is fairly easy to determine. Simply take a sample of a feed and weigh it. Then heat the feed sample slightly above the boiling point of water. Hold it at this temperature until the feed stops losing weight. Then weigh the feed. This weight is subtracted from the weight before heating. The difference between the two weights represents the amount of water driven off by the heat. To find the percentage of water, divide the dry weight by the original weight.

Another fairly simple analysis is to find out how much mineral is in the feed. Recall that minerals are inorganic chemicals. As such they will not burn. When feed is completely burned, a whitish-gray ash is left. If the weight of this ash is divided by the original weight of the feed before burning, the percent mineral, or ash, is obtained. The chemical analysis gets more complicated when you are determining how much protein is in a feed. Recall that protein is made up of carbon, hydrogen and oxygen plus nitrogen. Scientists have learned that protein is about 16 percent nitrogen. Using certain chemical tests, the amount of nitrogen in a feed can be determined. Multiplying this amount by 6.25 (16 percent nitrogen divided into 100=6.25) gives the amount of crude protein in a feed. It is called crude protein because it includes all nitrogen compounds. There may be some nitrogen compounds in the feed which are not true proteins.

Another test is for the amount of fat in a feed. Since fat dissolves in ether, a sample of the feed is heated in ether for several hours. Then the feed is removed, and the ether is evaporated. The residue that is left is the fat, or ether extract. is because fiber is hard to digest. Therefore, feeds with a It is important to know the fiber content of feeds. This high fiber content are less nutritious.

To find the fiber content, some of the feed is dissolved in a weak acid or alkali. Fiber (very complex carbohydrates) will not dissolve; it is left over. Any material that the weak acids or alkali will not dissolve is considered to be indigestible by animals. Keep in mind that the cells in the lining of the stomach secrete a weak solution of hydrochloric acid.

If the percentage of water, minerals, fat, fiber and protein are added together, the total will be something less than 100 percent. This difference is referred to as the nitrogen-free extract. This extract includes the more soluble carbohydrates, sugars, starch and some cellulose. All of these are readily digested in the digestive tract.

When the amounts of different nutrients in a feed are known, the quality or feeding value of the feed can be easily determined. By adding the digestible organic nutrients (protein, nitrogen-free extract and fat x 2.25), we can tell the “energy value” of a feed TDN - total digestible nutrients - is the term used.

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A great variety of feeds may be used satisfactorily for horses. In different parts of the world, horses are fed elephant grass, bamboo leaves, dried fish, turnips, beets, leaves of limes and grapevines, and lawn clippings. As a general rule, we should choose feeds that are suitable and readily available at the most economical cost. Therefore, we may say that the ABC's of choosing feeds for horses are based on knowledge of nutrient content and function of the horse, combined with experience of the horse owner.

In this lesson we learn about the content of energy, proteins, minerals, vitamins, and fiber or bulk contained in some of our most important feeds for horses. Also, we learn about correction factors to consider, such as quality, suitability, availability, cost, and convenience.

We gain experience by applying these ABC's to provide economical, satisfactory rations when we have a thorough understanding of the digestive system of the horse, the nutrients and their importance, and balancing rations for the horse.

TYPES OF FEEDS

We can conveniently classify feeds into three main types: (1) roughages, (2) concentrates, and (3) mixed feeds. Roughages include pasture forages, hays, silages, and byproduct feeds that contain a high percentage of fiber.

Concentrates are the energy-rich grains and molasses, the protein- and energy-rich supplements and byproduct feeds, vitamin supplements, and mineral supplements. Mixed feeds may be either high or low in energy, protein, or fiber; or they may provide “complete” balanced rations.

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ROUGHAGES

Wild horses live on roughage today as their ancestors did 55 million years ago when they were five-toed animals the size of a fox. Roughages are still important for active horses and may serve as the only feed for idle horses. Proper use of good quality roughages reduces the quantity of expensive concentrates needed and provides a plentiful supply of vitamins and minerals.

There are three main forms of roughages: (1) dry roughages, (2) silages, and (3) pastures. Dry roughages include hay, straw, and artificially dehydrated forages, which contain about 90 per cent of dry matter. Silages are formed from green forages such as grass, alfalfa, sorghum, and corn preserved in a silo at dry matter contents of 20 to 50 percent. Green, growing pastures provide forage that has a high water content and only 20 to 30 percent of dry matter.

There are two basic types of roughages: (1) grasses, and (2) legumes. The grasses are generally higher in fiber and dry matter than legumes. The legumes are generally higher in proteins, energy, vitamins, and minerals. Soil fertility, soil type, and climate influence the productivity and nutrient content of the various grasses and legumes. But the most important factor affecting the nutrient composition of grasses and legumes is stage of maturity.

As a plant grows older, it becomes less leafy, more stemmy, more fibrous, and less digestible. Timothy hay cut before bloom has about 160 percent more digestible protein and 35 percent more TDN than mature timothy. Mineral and vitamin levels are also higher in immature grasses and legumes, whether these roughages are in the form of pastures, silage, or hay.

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DRY MATTER CONTENT

DRY ROUGHAGES

In general, the best hay for horses is a good quality grass legume mixed hay. A good quality pure legume or pure grass hay is satisfactory if it is fed properly.

Grass hays such as timothy, oat, brome, bermuda, wheatgrass, native western mountain, etc. of equal quality have similar nutrient values. Prairie hay is much lower in protein than most other grass hays. The legume hays (alfalfa, soybean, peanut, lespedeza, and clovers) are generally higher in protein, energy, calcium, and phosphorus than grass hays. Mixtures of grasses and legumes are intermediate in nutrient content. Because the calcium level in legumes is about six times higher than the phosphorus level, a supplemental source of phosphorus might be needed to balance the Ca:P ratio in a ration high in legumes.

If we learn to identify the grasses and legumes by their leaves and blossoms, we can do a more intelligent job of buying. Also the head of grasses and the bud or bloom of legumes can tell us the state of maturity at which the hay was cut. Horses refuse and waste more late cut hay, which is already low in nutrient content.

Leafiness of hay is an important guide to feeding value because most of the nutrients are carried in the leaves. For hay to grade U.S. 1 or U.S. 2, 25-40 percent of its weight must be leaves. Leafiness is influenced by kind and species of forages, stage of maturity when cut, weather conditions while growing and while curing, and curing procedures. Leaves are shattered and lost when hay is raked or baled too dry.

Color of hay is another indication of quality and nutrient content. Good hay is a bright leafy green. Overly mature hay is pale, yellow, or brown. Hay that was rained on when it was nearly cured may be faded in color because of additional drying time and exposure to sunlight and air. This exposure destroys the carotene or vitamin A value. Heavy rain on nearly dry hay leaches carbohydrates or energy value from the hay and also causes a loss of these nutrients from fermentation. Hay that is baled before it is dry enough will lose nutrients through fermentation or “heating” in the bale, which sometimes starts a fire from spontaneous combustion. Even if it does not start a fire, heat of fermentation is energy value lost and produces a dull, dark hay that is usually dusty with moldiness inside the bale. Such hay is unacceptable for horses; therefore open and examine several bales of a prospective purchase if there is any question about its quality. Tight, clumpy, misshapen bales are subject to suspicion.

Odor of hay will vary according to species of grasses and legumes but should always be aromatic and pleasant. Lack of odor indicates over-maturity, bleaching, leaching, or old hay which probably has lost most of its vitamin A value. A stale, musty, unpleasant odor indicates that excessive fermentation has occurred. Dust is objectionable in any feed for horses. It not only reduces the palatability of the feed, but also can cause heaves and other respiratory trouble. Good timothy tends to be most dust-free of the hays. Pure legume hays tend to be more dusty than grass or mixed hays. Dustiness can be reduced by sprinkling the hay or other feed with water or water and molasses just before it is fed. Dehydrated roughages such as alfalfa leaf meal or pellets are made by processing lush-growing, highly nutritious forage through a heated dryer called a dehydrator. These dehydrated meals or pellets are usually rich in vitamin A value, B vitamins, and high quality proteins. They are used mostly as vitamin and protein supplements, but their high fiber content classes them as roughages.

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PROTEIN % IN HORSE FEEDS

SILAGES

Good quality silages are a suitable replacement for up to half of the hay or pasture allowance. Remember that about three pounds of silage are equivalent to one pound of hay because of the difference in dry matter content. However, spoiled, moldy, or frozen silages cause digestive upsets in horses. Silage that contains dead rats, birds, etc. can cause fatal botulism poisoning in horses.

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TOTAL DIGESTIBLE NUTRIENTS IN HORSE FEEDS (%)

PASTURES

Pastures can reduce feed costs and provide plenty of vitamins and good quality proteins. They are important for mares and foals, and night pastures especially are good for pleasure horses. However, an exercise lot with a few blades of grass is not a pasture. Such a lot or an overgrazed pasture of short forage can be a serious source of internal parasite infestation.

Horses should be rotated to “fresh” pasture every two weeks if possible. This will reduce internal parasite infestation and also increase the productivity of pastures, particularly if the pastures are small. Understocked, overgrown, coarse, and unpalatable pastures are sometimes clipped to freshen them up during the growing season.

Pasture forages are quite laxative in early spring. Legumes are more laxative than grasses. Therefore, laxative feeds such as linseed oil meal or wheat bran should be removed from the ration when horses first go on pasture, and their daily time on pasture should be short at first.

CONCENTRATES

Corn, oats, barley, and milo (sorghum grain) are the most important energy-rich grains. They contain about 70 to 80 percent of TDN (total digestible nutrients) including 7 to 10 percent of digestible protein. Wheat bran, rice bran, wheat middlings, rye middlings, and rice polish are byproduct feeds from the grain milling industry. The brans are somewhat laxative and bulky and usually contain about 65 percent of TDN of which 8.5 to 14 percent is digestible protein. Soybean oil meal, cottonseed oil meal, peanut oil meal, and linseed oil meal are called “protein supplements.”

They have about 75 to 80 percent TDN and 30 to 46 percent digestible protein. Mineral concentrates include: salt, or sodium chloride (NaCl); iodized salt (NaCl plus iodine); ground limestone, which supplies calcium (Ca); steamed bonemeal and dicalcium phosphate for calcium and phosphorus; and others. All of the vitamins can be obtained in concentrated form, singly and in various combinations.

Corn is similar to the other grains in nutrient content but is the richest in TDN and the lowest in protein, fiber, calcium, and phosphorus. Corn is the most readily available and most economical grain in most sections of the country. It can be used to full advantage if its deficiencies are offset by (1) good quality legume or grass-legume hay or pasture, (2) a suitable grain milling byproduct feed, or (3) a protein supplement. It is used in most mixed feeds and also as ear corn, shelled corn, or cracked corn. Cracking improves its digestibility, but finely ground corn is more apt to cause colic unless it is mixed with a bulky feed.

Oats are somewhat higher in protein than corn, much higher in fiber and much more bulky, and about 15 percent lower in energy. Nutrient content of oats varies considerably according to proportion of fibrous hull to nutritious grain.

Rolled or crimped oats is more digestible than whole oats. Oats with a grass hay such as timothy may be inadequate; some grass-legume roughage along with some corn or barley will assure a more complete ration. Oats are usually the most expensive feed grain in terms of cost per unit of nutrient.

However it is the safest and easiest to feed and goes well with other grains that tend to cause colic.

Barley rolled or ground medium fine is worth about 10 percent more per pound than crushed oats. Since barley may cause colic if fed alone, it should be mixed with at least 15 percent bran or 25 percent oats.

Milo (grain sorghum), like barley, should be crushed or ground and fed with bran or oats. It then has TDN and protein values intermediate between barley and corn.

Molasses is a concentrated appetizer and dust settler. It is sticky, sweet, and smells good. It contains 54 percent of TDN, very little minerals, no fiber, and no digestible protein. Unit cost of TDN is usually as high or higher than the cost of the same amount of energy as grain. However, either cane or sugar beet molasses is nearly always included at levels of 5 to 15 percent in commercially mixed rations.

Protein Supplements. A protein-rich supplement is needed when: (1) the roughage being fed is of poor quality, or (2) the pregnant or lactating mare or young stock requires extra protein to balance the ration. High protein feeds that are commonly used for horses are: soybean oil meal, linseed oil meal, cottonseed oil meal, and peanut oil meal. Protein quantity and quality in soybean and peanut oil meals is higher than in linseed and cottonseed oil meals. Linseed oil meal is the lowest of these in protein and usually is not the most economical source of protein, but it is used for its laxative quality and to improve the luster and bloom of hair coats. Although these protein supplements are high in energy value also, feeding excessive amounts is useless, expensive, and causes digestive upsets.

Byproduct feeds. Certain byproducts from the milling industry are useful, economical horse feeds. Wheat bran and rice bran are highly palatable and slightly laxative, therefore they improve rations of grass hay and corn, barley, or milo. The brans are especially good sources of two B vitamins, thiamine and niacin, and supply fair amounts of protein and energy. Wheat middlings, rye middlings, and rice polish are lower in fiber and higher in energy than the brans; they may cause colic and other digestive upsets if they comprise more than 25 percent of the concentrate ration.

Your 4-H horse project offers an opportunity for you to learn how to balance a ration. To accomplish this, you must be accurate in your addition, multiplication, division and subtraction. You will be working with percentages, so be sure and watch decimal placings. You can use Nutrient Requirement Tables in two ways:

1) To check the ration being fed to see if it is balanced, and

2) To formulate an adequate ration for your horse.

Follow this procedure in checking through the example ration and in working out a ration for your horse on the blank sheet.

1) Determine the age, weight and type of work your horse is doing.

2) Fill in Section 3 of the enclosed work sheet from Table 1, Daily Nutrient Requirements of Horses.

3) List available feeds in Section 1 of your work sheet, giving attention to each column. If you have actual analysis on your feeds, use these. If not, take average analysis from Table 2.

4) Weigh the amount of each feedstuff being fed daily. If a mixed feed is being used, you can either find out the amount of each feed ingredient that is in the mixture or use analysis of the mixture from the feed tag.

5) Multiply each figure in Section 1 by the pounds fed daily (Section 2, column 1). Record the results in the appropriate columns of Section 2 on your work sheet.

6) Add the columns in Section 2. This gives the total amount of each nutrient in your horse ration.

7) Check these totals against the “Daily Nutrient Requirements” listed in Section 3 of your work sheet. If the “requirement” is more than the totals in your ration, you will know that your ration is inadequate. Your next step is to find a feed ingredient that is a good source of the deficient nutrient and either substitute this new feedstuff for one you are now using or add this new ingredient to your horse ration. After doing this, you should refigure your totals to be sure other nutrients are not out of balance. Excesses of some nutrients can interfere with use of others in addition to being a waste of feed and money. For example, excess calcium can prevent complete utilization of phosphorus in a ration.

There are good reasons why you should be concerned with maintaining the proper health of your horses or ponies. First, you have a responsibility to all animals entrusted to your care to protect them from injury, sickness and pain. Secondly, any time your horse is ill it will prevent you from using him.

Thirdly, if your horse needs treatment, it will usually cost you time and money. If we take the horse industry as a whole, we find that thousands of dollars are lost each year because horse owners did not follow the prescribed practices of good breeding, feeding, management, and disease prevention. This is sad, indeed, since the knowledge and materials necessary to prevent most of these losses are readily available.

Animal scientists have discovered many practices which horse owners find beneficial in the maintenance of healthy horses. There are many fine drugs, vaccines, disinfectants and other products manufactured today that can be used successfully to help keep horses healthy. Fortunately the people in veterinary medicine are ready and willing to help in the wise use of these materials and in helping you to set up a sound health program for your horses.

There are many preventive measures which are good common sense ideas with scientific principles behind them.

Some of the more important ones are listed below.

1) Feed your horses a nutritionally balanced ration, in sufficient quantities in the correct manner.

The scientific basis for this recommendation is: a horse's well-being depends largely on its nutrition. If the level of nutrition is high, the body defenses against diseases will be stronger. This also applies to the problems of internal parasites. Unsoundnesses of the feet and legs are sometimes traced to deficient rations. The same is true of other abnormalities such as infertility and abortion. It is possible to overfeed horses and by so doing create serious problems. A horse may founder, become temporarily infertile or aggravate respiratory problems from being over- fed. Some of these troubles are caused from feeding moldy or dusty feed or from feeding or allowing access to cold water too soon after heavy work.

2) Provide clean, healthful quarters for your horses. The scientific basis for this recommendation is:

Disease organisms often grow and thrive in organic waste. Flies and insects as well as vermin, which also harbor disease, thrive under filthy conditions. Removing the source (reservoir) of the disease organism lessens the chances of disease.

If your horse is kept in a clean environment, his body will not be constantly fighting to ward off disease. Therefore, he will make better use of his feed, will feel better and perform better because of less stress from disease.

Horses do best when allowed plenty of freedom to exercise and plenty of clear fresh air, provided there are no drafts. Most respiratory troubles develop from keeping horses in tight barns which are too warm and humid.

3) Carry out a planned immunization and parasite control program. The scientific basis for this recommendation is: contagious diseases are caused by microorganisms, mostly bacteria and viruses. However, your horses can develop defenses against many microorganisms. These defenses are the antibodies in the blood. By vaccinating your horses against specific diseases they will build up their antibody defenses against possible invasion by microorganisms.

The secret of successful immunization is to have a methodical plan, developed in consultation with your veterinarian and then to carry it out before disease strikes. Vaccination after your horses have been exposed to disease will seldom give them enough time to build up their defenses to a large enough degree. You might sustain serious losses in such a case.

Horses are often inoculated against tetanus since this organism is usually present in horse stables. Internal parasites can cause stunting, illness and even death if not controlled. They are particularly harmful to foals and colts up to two years of age. Periodic examination of fecal samples from your young horses by your veterinarian will give you information on the extent of the problem. The most scientific way to prevent disease and parasitism in your horses is to plan a total immunization and parasite control program with your veterinarian. You must have your horses vaccinated at the right time, with the right vaccine and by the best method to be sure they will build up an immunity. You must also treat for parasites at the proper time and with the proper material in the prescribed way to successfully protect your horses.

4) Get an accurate diagnosis of the disease problem from a veterinarian.

The scientific basis for this recommendation is: Correct diagnosis of illness or abnormal conditions in your horses is necessary before they can be treated intelligently. Improper treatment based merely on supposition can result in loss of time and money or even the animals involved. A diagnosis requires much specialized knowledge and many procedures. Veterinarians have this knowledge and also the equipment necessary to make the study. If they lack in either facilities or knowledge in a special situation, they can call on the state diagnostic laboratories and scientists for assistance.

5) Keep your horses well exercised, groomed and feeling fit.

The scientific basis for this recommendation is: if your horses are confined and cannot exercise by themselves they will lose muscle tone, they may become stiff or lame and their digestive systems will not function as effectively. Horses in their natural state had the opportunity for unlimited exercise in a clean, outdoor environment. This enabled them to keep fit which meant they were better equipped to ward off disease and unsoundnesses.

6) Consult your veterinarian. Plan a disease prevention and parasite control program with him. The scientific basis for this recommendation is: preventing disease is more effective than treating your horses after they become sick.

Your local veterinarian is best qualified to help outline a disease control program. He is trained in his field and he is acquainted with the major disease problems in your particular area.

By keeping in constant touch with your veterinarian he knows the history of your horse or horses and will be in a better position to make an accurate and rapid diagnosis. Disease prevention will probably be most effective when you and your veterinarian work together in all phases of the disease prevention program.

An infectious disease is one caused by the presence in or on an animal body of a living foreign organism, which by its presence creates a disturbance leading to the development of symptoms.

A contagious disease is one that may be transmitted from one animal to another by direct or indirect contact. All contagious diseases are also infectious, but it does not follow that all infectious diseases are contagious. For example, tetanus, caused by organisms which live in the soil is infectious but not contagious since it is not transmitted directly from one animal to another.

Some infectious diseases are highly contagious. Some are slightly contagious and a few are not contagious at all. How contagious a disease is depends upon how the disease organisms are eliminated from the body of the diseased animal, their opportunity for reaching others and their ability to produce disease in the new hosts.

Disease-causing organisms vary greatly in their ability to produce disease. When the ability to produce disease is great, the organisms are referred to as virulent.

Animals also vary in their ability to resist or repel disease-producing organisms. An animal's ability to resist a particular organism is known as immunity. The immunity of an animal may vary from slight to absolute.

Sometimes animals develop disease-resisting properties within their bloodstream. These properties repel the invading organism. Sometimes these properties are strong enough to remain for the life of the animal (permanent immunity). Other times they pass in a few months or a year (temporary immunity). Vaccination is a means of artificially stimulating the immunity of the animal without giving it actual disease. To do this the virulence of organisms is lowered until it no longer possesses the ability to actively cause disease but can stimulate the development of immune properties in the body of the host animal. These live but attenuated organisms are known as a vaccine. Other times the organisms are completely killed and the products of their growth used to stimulate immunity. This preparation is known as a bacterin.

Because disease-producing organisms reach a host animal does not always mean that the animal will develop disease. Sometimes the animal's resistance is high enough or the virulence low enough that the organisms are destroyed by the host. This process is continually going on as organisms capable of producing disease are constantly present. If something happens to lower the resistance of the animal or to raise the virulence of the organism, then a disease process can start. If the host and invading organisms reach a standoff, the infection makes little or no headway but persists for a long time. This is known as a chronic infection.

If the invading organisms rapidly overcome the resistance of the animal, then death usually ensues unless rapid resistance to the organism is developed by the host or suitable treatment is received. These cases are known as acute.

During the course of any disease many organisms escape from the host. Sometimes they are eliminated with blood, or from an abscess. Sometimes they are passed out with droplets of moisture which accompany a cough or a sneeze as in respiratory infections. Sometimes the organisms are eliminated through fecal material or urine as in intestinal or urinary infections. (The virus of rabies is eliminated through the salivary glands and usually enters the body of the new host through a bite or wound and is not normally spread otherwise.)

Occasionally an animal and the infected organism will reach the point where the organism is unable to cause serious damage to the host, yet the host is unable to eliminate the organism. This situation may continue throughout the lifetime of the animal. Such animals are capable of shedding organisms causing disease in contact animals. We refer to these animals as carriers. Carriers may not show symptoms of disease but are a source of great danger to others who lack the same amount of resistance. The carrier is one of the great problems of control of many infectious diseases. Animals that are obviously diseased may be recognized, but there is no simple way of recognizing carriers.

There are many sources of infection for your animals. We usually think of direct contact with the diseased individual.

Disease may also occur when inanimate objects carry infection from one animal to another. This can occur in a trailer, a railroad stock car or trunk contaminated with the fecal material and not properly cleaned and disinfected. Contact with apparently healthy disease carriers is a major hazard. These carriers may infect others directly or indirectly as readily as the obviously diseased animal.

Infection from soil. Certain organisms live in the soil and are able to produce disease in animals if chance carries them to the tissues (example: tetanus). Disease may be contracted from food and water that has been contaminated by a diseased animal (example: leptospirosis).

Air-borne infections occur when droplets of moisture are sneezed or coughed into the air (example: strangles or respiratory infections).

Some infections are carried by bloodsucking insects (example: Equine encephalitis or sleeping sickness). Disease Prevention. Most contagious diseases (1) avoiding contact with sick animals, (2) preventing indirect contact by using clean trucks. Insist on new grain sacks for purchased feed. Keep visitors from other stables with manure or dirty clothing from contacting your animal, his feed or water supply. Use private water pail at fairs or shows, etc. (3) Raise your animal's resistance by good feeding, sensible use and care and vaccination when indicated. Normal use of the animal prevents completely isolated or 100% protection from exposure. Therefore you should strive to raise the resistance of your animal by keeping him well nourished and in a good state of health. Do not allow an animal to become too tired or to chill. Chilling might occur from riding for long distances in cold, windy, uncovered trucks or being tied in a cold rainstorm. Such stresses greatly lower an animal’s resistance to disease.

Always provide clean drinking water, and when horses are gathered in large groups, water your horse from an individual bucket, drawing the water directly from the tap, not dipping it from the trough. Many people go to the bother of providing their own water bucket at fairs or shows then make the mistake of filling the bucket from a common trough.

Vaccination will raise an animal's resistance to many diseases. Strangles (or distemper), tetanus (or lockjaw) are examples. Your veterinarian can advise you as to diseases common in your area that can be prevented by vaccination.

General information concerning common diseases of horses is presented in table 1. For additional information of diseases of horses, contact your veterinarian.

Have you ever been aggravated by swarms of mosquitoes, irritated by ticks and chiggers, or agitated by fleas? These discomforts and many more are experienced by some horses for extended periods of time because of

external parasites. A parasite is defined as “a plant or animal living on, in,

or with another living organism (its host) at whose expense it derives food and shelter.” External parasites of horses usually bite (with the exception of certain flies) and/or suck blood for food, and use body temperature and the hair of the host for comfort and shelter.

Foals and young growing horses are especially susceptible to all types of parasites, which may result in temporary or permanent lack of development.

External parasites are a problem to many horses. They are often associated with improper nutrition, mild forms of disease, stress, and sometimes conditions of general neglect. External parasites are easier to eradicate or control than internal parasites, but response to treatment may be disappointing unless a total health program is practiced. The most common external parasites are (1) flies, (2) lice, (3) mites, (4) ticks, and (5) a fungus causing ringworm. Both ringworm and mange mites are communicable to man.

Flies

Flies are a constant source of annoyance to horses, making them restless and ill at ease. The house fly and face fly feed on skin, nasal and eye secretions, or debris, but do not bite. The tenaciousness of the feeding face fly makes its presence particularly annoying to horses. They are commonly found in the northern half of the United States. Horn flies, stable flies, and deer and horse flies are biting insects that suck blood. Since they show a preference, some horses are severely harassed by these pests. Biting flies can be vectors of serious diseases such as encephalomyelitis.

Blow flies are common to large areas of the United States, and effect damage by laying eggs in wounds. One type hatches into maggots which feed on dead tissue, retarding healing and enlarging the wound. The other type hatches into screwworms, which feed on live tissue, causing severe damage and sometimes death. Both types are easily eradicated by cleaning the wound and applying a proper medicant.

Control

Fly control is best effected by removal of waste and decaying vegetable material. Manure should be stored in covered containers or spread thinly (for rapid drying) on fields not used by horses. Remove moist hay, straw, garbage. and grain frequently during warm weather. Use screens when practical.

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Life Cycle

The four stages of the life cycle are the egg, the larva, the pupa, the adult. House, stable, and horn flies commonly lay their eggs in manure or occasionally in decaying vegetation or any moist collection of spilled grain. Face flies lay their eggs in fresh manure on pastures. Horse and deer flies deposit eggs in the mud of swamps, salt marshes, or on vegetation near water.

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HORSE FLY

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STABLE FLY

Treatment

Successful treatment of flies varies from one part of the country to another and will be influenced by the degree of immunity they have established for a specific product. For this reason a qualified person should be consulted for recommendation in a given area. Regardless of the area, pesticides should be considered poisonous and should be regarded with extreme caution. Read the directions carefully and follow them closely. Do not permit sprays to contaminate feed or surfaces that horses will lick. Do not store them where they may accidentally get into feed. Baits are effective but poisonous and should be placed out of reach of horses because many contain enough sugar to induce their consumption. Strands or cords treated with insecticide and hung in stables are often effective. Daily sponging or spraying may be necessary to give protection from horse flies and face flies. For those insecticides commonly used and recommended for your area, contact your local county agent or veterinarian.

Lice

Lice that infest horses are of both the biting and sucking kind. Long hair is conducive to maximum reproduction and spread of lice, thus they are often observed in poorly groomed and poorly housed horses, especially in early spring. Symptoms include rubbing, biting, general unthriftiness, and patches of skin denuded of hair.

Life Cycle

The adult lice attach their eggs to the hair, usually close to the skin (the so-called nits). Here they hatch in from 11 to 20 days. The young lice reach maturity and the female begins laying eggs when she is 11 to 12 days of age. Lice live their entire lives on the host, and can exist only about three days when off the host animal.

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BITING LICE

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SUCKING LICE

Prevention

Proper feeding, grooming, and clean stabling will do much to prevent louse infestations. Lice may be carried from one animal to another on harness, saddles, blankets, brushes, or curry combs moved directly from a lousy animal to one free from lice.

Treatment

Horses may be dipped, sprayed, sponged, or dusted thoroughly for lice control. The treatment should be repeated in two to three weeks in order to destroy the lice hatching from eggs not destroyed by the first application. Contact your county agent or veterinarian for the recommended insecticides most commonly used in your area under prevailing regulations.

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SARCOPTIC MANGE MITE FEMALE MAGNIFIED 100 TIMES

Mites

Mites are microscopic creatures that cause horse mange. Positive identity is difficult because skin scrapings must be examined carefully under a microscope. Three genera exist: Sarcoptes, Psoroptes, or Chorioptes. Sarcoptic mites burrow under the skin scurf where they lay eggs and reproduce.

Chorioptic type may cause foot mange resembling scratches, although all three may cause mange on any part of the body. Symptoms include irritation, itching, inflammation, loss of hair, crusty scab formation, and folding of the skin.

Life Cycle

Female mites lay from 10 to 25 eggs during the laying period, which lasts from 12 to 15 days. After this period the female dies in the burrow. Eggs hatch in 3 to 10 days into young mites. After passing through several molts, they reach maturity and are ready to begin egg laying again in from 10 to 12 days.

Treatment

Mange is difficult to eradicate in any species of animal. Experience indicates that infested animals should be retreated every 7 days in order to gain control. Dusts are not effective. Spraying or thorough wetting with a brush-washing technique is necessary to reach the well-hidden mites. Your county agent or veterinarian are your best sources for information regarding the prevailing regulations for the kinds and use of the insecticides.

Ticks

Ticks are a problem to horses in many parts of the country. Like other biting insects, they are vectors of some serious diseases. Piroplasmosis recently infected over one hundred horses in the southeastern part of the United States. In 1960, the red tick, carrier of African horse fever, was identified for the first time in this country, in zoo animals in Florida.

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TICKS - MALE

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TICKS - FEMALE

Life Cycle

The four stages include the egg, the six-legged larva or seed tick, the eight-legged nymph, and the adult. Transition from one stage to the next occurs by molting. The number of generations produced annually varies from one every two or more years up to four or five per year, depending on the species. All ticks attach to the host and feed on blood.

Treatment

In areas where ticks are a serious problem, dipping entire animals must be resorted to. If only a few ticks are found, swab them with cotton dipped in alcohol or chloroform. Since ticks breathe by means of spiracles or holes found on the abdomen, this tends to anesthetize or suffocate them. Several insecticides are available. Follow the recommendations of your county agent or veterinarian regarding their use.

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RINGWORM OF THE HORSE DUE TO TRICHOPHYTON EQUINUM

Ringworm

Ringworm is caused by various species of fungi, arranged in circles on the skin. If penetration is deep enough, severe itching results, and secondary infection may lead to abscesses. The lesions are usually covered with greyish crusts through which short hairs protrude.

Treatment

If only a few lesions are present, soften crusts with warm soap and water and remove, dry the area, and paint with tincture of iodine daily for one to two weeks. If lesions are extensive, contact your veterinarian, since there are many new fungicides more effective than iodine. When treating or handling infected horses, use rubber gloves and wash hands thoroughly after treatment. All scrapings should be carefully disposed of. Children are particularly prone to ringworm infections.

Under the best management conditions horses harbor some parasites. Their effect is not spectacular or may be unnoticed, but they decrease work efficiency and cause discomfort. Heavy infestations render horses useless and may cause death or permanent damage. For these reasons atotal health program should be effected.

PRECAUTIONS

MOST INSECTICIDES ARE POISONOUS TO CONCENTRATES PRIOR TO DILUTION FOR APPLICATION. ALL PRECAUTIONS ON THE LABELS SHOULD BE FOLLOWED FOR THEIR USE AND STORAGE. READ THE LABEL CAREFULLY! AVOID CONTAMINATION OF FEED AND WATER WITH INSECTICIDES.

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HORSE HAIR INFECTED BY T. EQUINUM ECTOTHRIX TYPE OF PARASITISM, X522

According to Webster's Dictionary, a parasite is a plant or animal living in, on, or with another living organism (its host), at whose expense it obtains food and shelter. More than 150 different kinds of parasites have been found to infest horses. Almost all horses harbor some parasites. External types include lice, flies, ticks, mange, and ringworm. The internal types, which we will deal with in this lesson, include strongyles or blood worms, ascarids, stomach worms, pinworms, and bots.

Every horse owner should have his animal on a parasite prevention and control program. In order to draw up such a program, it is important to know the life cycle of the various worms so that proper preventive and treatment procedures can be followed.

Economic Importance

The effect of the presence of worm parasites are not usually spectacular. However, they do cause decreased work efficiency, poor utilization of food, are one of the causes of colic, may be the cause of intermittent lameness, may cause a chronic cough and bronchitis, and occasionally death due to blood clot. Some adult worms produce toxins that destroy red blood cells, leading to an unthrifty anemic condition. Immature worms migrating through body tissues open the way for bacteria and fungi to enter, causing other serious diseases.

Prevention of Parasitism

Internal parasites gain entry to the animal body in the form of eggs, larvae, or adults. This may be largely prevented by various forms of management which break the life cycle of the parasite. Those worms already present will have to be killed by drugs, depending on the kind of parasite present. The following practices have been found to be effective in reducing parasite numbers:

1. Do not feed hay or grain on the floor. This prevents contamination of feeds with manure, which may contain large numbers of parasite eggs or larvae.

2. Do not allow horses to obtain water from barnyard pools or water holes on pasture, since manure drainage into these areas makes them a source of internal parasites.

3. Clean stalls and rebed as often as possible so that there will be less chance of internal parasites getting on feeds from fecal material.

4. If the stall floor is of earth, remove ten to twelve inches once or twice yearly and replace with clean soil.

5. Remove manure from premises daily and either spread on a field where horses will not graze for a year or where the field will be plowed and reseeded before horses have contact with it.

6. If manure must be left near the barn, keep in a covered pit where it can heat and thus kill parasite eggs and larvae. This will also prevent fly breeding.

7. Small, heavily used pastures tend to build up a heavy parasite load. Small exercise yards should not contain pasture grasses which encourage animals to eat contaminated material. It is best to have them gravelled.

8. Rotate pasture plots as frequently as possible to break the life cycle of the parasites.

9. Flies should be prevented from breeding by keeping surroundings free from manure, wet straw, and bedding.

10. Grain should be kept in covered containers away from flies, birds, and rodents, which may carry parasites from farm to farm.

Treatment

Treatment is a necessary but small part of the total parasite control program. Major emphasis should be on prevention. Even though adult worms are eliminated from the animal, damage has already been done by larval migration through body tissue. All drugs used for worming are dangerous and must be used with extreme care. In most cases, it would be best to have your veterinarian perform this service.

A regular program for worming horses should be adopted in cooperation with your veterinarian. Horses should be wormed in the fall after the first killing frost, and again in the spring before they go out to pasture. If strongyles are a particular problem continuous low-level feeding of phenothiazine should be considered.

In some areas, worm control programs are organized on a community or county basis. Since some of these parasites are transmitted by insect vectors, area action tends to reduce the possibility of this type of transfer. Such projects should be considered with your veterinarian, your county agent or your 4-H club leader.

Bot Flies

There are at least three species of horse bot flies. It their habit to hover about the horse, and then quickly darting toward the animal they glue individual eggs to the hair in a matter of seconds. The female of the common bot usually lays up to 500 eggs. Eggs are usually deposited on the hair of the forelegs. although they may be deposited on the mane, shoulders, belly, chin, and occasionally the flanks.

The horse tends to lick or bite itself where the eggs are attached, thus stimulating hatching, and the newly-hatched larvae are taken into the horse's mouth in this manner. Some larvae burrow into the tongue and migrate through the body tissues until they finally arrive in the stomach where they attach to the stomach wall. They arrive in the stomach in three to four weeks. They mature in the stomach in ten to eleven months, at which time they release their hold on the stomach wall and pass out with the animal's feces. Mature larvae burrow into the ground and change into pupa stage. In fifteen to seventeen days the mature bot fly emerges from the pupa case and mates to begin the cycle again.

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BOT FLY

Stomach Worms

There are at least ten different types of stomach worm, four of which are known to cause lesions, resulting in an inflammation of the stomach wall. The larval forms of the larger stomach worms are thought to be responsible for a skin disease of horses called “summer sores.” The larger stomach worms are approximately an inch to an inch and a half in length. Adult worms in the horse's stomach lay eggs which are passed out with the manure and picked up by maggots (larval forms) of the house fly or small stable fly. The stomach worm eggs hatch in the head region of the adult fly where they had come to rest as the fly matured. Horses probably swallow infested flies accidentally, or larval worms may leave the flies while they are feeding on the moisture around the horse's lips. Once in the horse's mouth, they are readily swallowed and mature into adult worms in the horse's stomach to repeat the cycle.

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BOT LARVA

Ascarids (intestinal worms)

Adult worms in the small intestines deposit eggs which pass out with the manure. During warm weather, embryos develop within the eggs and are infective in about two weeks. Embryonating eggs are swallowed by grazing horses, the embryos are liberated in the small intestine, penetrate the gut wall, and are taken by the blood stream to the heart and lungs. After about one week's period, the larvae escape from the lungs, migrate up the trachea to the throat region where they are once again swallowed and the worms develop to maturity in the small intestine. Adults are approximately nine to twelve inches in length.

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LIFE CYCLES STOMACH WORMS LIFE CYCLES INTESTINAL ASCARIDS

Strongyles (blood worms, palisade worms)

The horse strongyles are a large group of approximately forty species infesting horses. Most of them are less than an inch in length and scarcely visible to the unaided eye. They are usually found firmly attached within the host, sucking blood. Female worms deposit large numbers of eggs which leave the horse with the manure. After the eggs hatch, the larvae molt twice before becoming infective. Infective larvae climb to the upper portions of pasture grasses and are usually swallowed by horses during grazing. Larvae migrate to various organs within the body, depending somewhat upon the species. Those that favor the walls of the arteries are responsible for certain types of lameness and even death due to embolism by restricting or blocking blood flow in the arteries.

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LIFE CYCLES STRONGYLES

Pinworms

Pinworms are approximately two to three inch long white-appearing worms with long slender tails. They are frequently seen in the feces of infected animals. The worms mature in the large intestines, and females full of eggs proceed outward through the small colon and the rectum, sometimes crawling out of the anal opening. The irritation causes infested animals to rub themselves against posts and other objects. Adult worms in this manner are crushed, at times leaving the eggs glued to the anal region. Normally, however, the eggs develop in manure and are picked up during grazing or feeding by horses to repeat the cycle. The vigorous rubbing of the posterior parts results in the loss of hair and occasionally injury may result in secondary infection. Fourth stage larvae are also found attached to the mucosa of the colon and are voracious feeders.

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INTERNAL PINWORMS TYPES AND SIZE

GLOSSARY

• Anemic (a ne'mik). Deficient in red corpuscles of the blood; a state causing paleness, weakness, heart palpitation.

• Bronchitis (bron kitis). Inflammation of the bronchial tubes (Extensions of the windpipe).

• Colic (kolik). An acute abdominal pain; may be caused by a great variety of disorders.

• Embolism (em bo lizm). The lodgment of an abnormal or foreign particle, such as an air bubble or blood clot, in a tube or canal of the circulatory system, which tube being too small to permit its passage.

• Embryos (em bri oz). Organisms in the early stages of development, as before hatching from the egg.

• Insect vector (vek ter). An insect which carries and transmits disease-causing microorganisms.

• Larva (lar va). The immature, wormlike form into which certain insects hatch from the egg.

• Maggot (mag ut). A soft-bodied, grublike, footless larva of an insect, as of the housefly; applied especially to forms living in decaying matter.

• Molt (molt). To cast off or shed the hair, feathers, horns, outer layer of skin, etc., being replaced by new growth.

• Parasite (par a sit). A plant or animal living in, on, or with another living in, on, or with another living organism (its host), at whose expense it obtains food and shelter.

• Pupa (pu pa). An intermediate, usually motionless, form assumed by metabolic insects after the larval stage, and maintained until the beginning of the adult stage; a chrysalis.

• Trachea (tra ke a). The main tube of the respiratory system; the windpipe.

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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