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Publication #AN119

Florida Cow-Calf Management, 2nd Edition - Managing Reproduction1

Mike Fanning, Jim Selph, and Shep Eubanks2

Reproductive efficiency is the single most important factor affecting your net returns as a cow-calf producer. You should have several goals in managing the reproduction of your beef herd:

  • Obtain a live, healthy calf from every replacement heifer by the time she is 2 years old.

  • Obtain an additional calf from each cow every year she remains in the herd.

  • Concentrate the calf crop into a short calving season.

(You might also want to use genetically superior herd sires through artificial insemination.)

To accomplish these goals, you must focus on the following practices:

  • Proper nutrition of the brood cow

  • Disease prevention

  • Minimizing calf death loss

  • Using fertile bulls

  • Culling nonbreeding cows

  • Breeding heifers 21 days earlier than the mature cow herd

Reproduction in the Cow

The cow's reproductive tract is located in her pelvic and abdominal cavities and consists of a pair of ovaries, a pair of oviducts (also called fallopian tubes), the uterus, cervix, vagina, and vulva (see Figure 1).

Figure 1. 

Diagram of the cow's reproductive system.

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Ovaries—Reproductive glands, which produce the female sex cells (called eggs, or ova) and the hormones estrogen and progesterone. Each egg is produced in a blister-like structure on the ovary called a follicle. There are cells in these follicles that produce estrogen. High levels of estrogen cause the cow to “come into heat” and stand to be ridden by other cows or bulls. Once it releases an egg (ovulation), the follicle changes to a corpus luteum or “yellow body.” The corpus luteum then produces progesterone (the “pregnancy hormone”), which is vitally important to pregnancy, should conception occur.

Oviducts—A pair of tubes that extends from the ovaries to the uterine horns. Immediately following ovulation, the egg is caught by the funnel-like portion of the oviduct and travels through the oviduct to meet the male sex cells, or sperm.

Uterus—In a cow, the uterus consists of a body and two horns. The body, located near the cervix, is the site for semen deposition during artificial insemination (AI). Sperm cells in the semen travel from the body of the uterus through the uterine horns to the oviducts. Fertilization occurs in whichever oviduct contains the egg. The corresponding uterine horn then houses the fetus during its initial stages of development.

Cervix—Forms a “gateway” between the uterus and the vagina. The cervix is tightly closed during pregnancy, but it is relatively open and very moist during the cow's period of heat.

Vagina—Functions as the “birth canal” during calving, and the site for semen deposition when the cow is serviced by a bull. There is a “blind pouch” in the vagina that bears little significance, except it often poses a problem for inexperienced AI technicians who may mistakenly place the tip of the insemination rod into this vaginal pouch rather than into the uterus.

Vulva—The external opening, or entrance, to the cow's reproductive tract. The vulva becomes swollen and moist during the period of heat (estrus). It also becomes very swollen and relaxed as calving (parturition) approaches.

Estrus, ovulation, and pregnancy are controlled by hormones. Linked in a cycle with ovulation, heat is the time when the cow will accept a bull. Heat usually lasts 14 to 18 hours. Ovulation then follows 30 hours after the onset of heat. If the egg is not fertilized, pregnancy does not occur, and the cycle repeats itself in about 21 days (see Table 1).

If it is fertilized, the egg begins a series of cell divisions as it migrates down the oviducts. It then attaches to the wall of one of the uterine horns, where it is nourished during pregnancy. The gestation period (pregnancy) lasts about 283 days. Management during calving is discussed in following sections.

Selection and Management of Replacement Heifers

Replacement heifers are “reinforcements” for the herd, used to either replace cows that have been culled, or to increase herd size. Consider replacement heifers as investments in the future; your management practices need to ensure that they calve early. Choose replacement heifers that, once introduced, possess the ability to remain in the cow herd for a long time.

Any successful program for developing replacements begins prior to their weaning and continues until heifers have rebred following their first calf. You should focus on three problem areas:

  • Low pregnancy rates for yearling heifers.

  • High losses at first calving.

  • Low percentage of heifers rebreeding for their second calf.

Selection. No single set of selection criteria could represent the priorities of all producers. However, since reproduction has more to do with profitability than any other trait, it should definitely be emphasized. Heifers should appear to possess a high degree of fertility, good frame size, and structural soundness. The fertile heifer looks feminine, and has a normally developed udder. (With purebred cattle, adhere to those standards established by the breed associations, provided they are not simply fads.) Adequate growth is absolutely essential to maintain a scheduled breeding and calving season.

Selection is a continuous process throughout a heifer's development. There are several stages at which heifers should be evaluated, and kept or culled:

  • Weaning

  • 1 year of age

  • After breeding season

  • After first calf is weaned

To allow for culling at these various stages, select more replacement heifers than you need.

At weaning, evaluate heifers for weight, height, and structural soundness, as well as other traits that are important in young herd replacements. Rank heifers on the basis of actual weaning weight and adjusted weaning weight. Eliminate heifers that (for any reason) are not structurally sound. Then, save those heaviest calves that have acceptable frame size and are not overly fat. At first culling, save about 50% more heifers than you need for herd replacements.

Evaluate heifers again between 1 year of age and the start of breeding season. A few heifers might be eliminated at this time due to unthriftiness or structural problems.

The next critical time for selection is about 2 months after heifers have been exposed to a bull for a short period of time (45 to 60 days). Heifers should be pregnancy checked; all that are not bred should be culled. If more heifers are bred than needed, keep those that were bred early; the others can be sold as bred heifers.

Final evaluation of a heifer occurs at the weaning of her first calf. Those that do not rebreed after their first calf, or wean a poor calf, should be culled.

Management and Breeding. Heifers of primarily Bos taurus breeding should be bred to calve at 2 years of age. Lifetime production is greater for heifers calving at 2 years of age than for those calving at 3 years of age. Heifers of primarily Bos indicus (Brahman) breeding should be bred at 2 years, to calve at 3 years of age. Management is the factor critical to successful calving at 2 years of age.

To breed Bos taurus heifers as yearlings, they must reach puberty (first fertile heat) by 14 to 15 months of age. Most heifers will reach puberty by this time if they have gained enough weight. A good rule of thumb is that heifers should be cycling normally by the time they reach two-thirds of their mature body weight. Table 2 lists estimated weights at which 90% of heifers should be cycling.

Your goal should be for a high percentage of heifers to become pregnant. To meet this goal, you must focus on the time period from weaning to breeding. Heifers should be fed adequately during this time period to gain enough weight to reach their “target weight” by the start of the breeding season (Figure 2). One should sort heifers into feeding groups to meet the required ADG to reach their “target weight” (younger, lighter heifers vs. older, heavier heifers). Following is an estimation of ADG to reach “target weight” by the start of the breeding season:

Figure 14. 

Heifers calving for the first time (especially those calving at 2 years of age) are more prone to problems during delivery. The primary source of calving difficulty is a calf too large for the birth canal. Thus, efforts to minimize calving difficulty should be directed toward reducing the birth weight of calves and/or selecting heifers of adequate size to deliver normal-sized calves.

Figure 2. 

Weaned heifers should be separated from the cow herd and fed to reach two-thirds of their mature weight by the start of breeding season.

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Commercial producers should choose a sire (or sire breed) known to produce calves that are small at birth. You can expect trouble from mating large-framed, heavily muscled bulls to smaller, medium-framed yearling heifers. However, certain bulls in every breed are genetically predisposed to sire calves that are small at birth. Breed associations and companies that sell semen give estimated progeny differences (EPDs) for birth weight and calving ease. Use this information.

Pelvic area measurement is a management tool which can be utilized to assess the size of the maternal birth canal. Well-grown heifers with greater pelvic area tend to have less calving difficulty. Pelvic area measurements should be used when breeding heifers to calve at 2 years of age. Pelvic area should be measured at 12 to 14 months of age and should be a minimum of 140 cm2. Take pelvic height (PH) between the sacrum and the floor of the pelvis. Pelvic width (PW) is measured at the widest point between the sides of the pelvis. These measurements can be easily taken via rectal palpation. Figure 3 shows where pelvic measurements should be taken. Pelvic area is calculated as a simple product of PH x PW. Breeding heifers to calve at 3 years of age reduces the occurrence of calving difficulty. These heifers are closer to reaching physical maturity. However, this practice results in a decrease in lifetime production.

Figure 3. 

Location of pelvic height (PH) and pelvic width (PW) should be measured to determine pelvic area.

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Reproductive tract scoring (RTS) is another management tool to use when evaluating replacement heifers. An RTS indicates if the heifer has reached puberty and whether or not she should be kept as a replacement heifer for your herd. AN RTS consists of palpating the reproductive tract and examining the uterine horns for size and tone and the ovaries for the presence of a corpus luteum (CL). The scoring system ranges from one to five. A score of one indicates immature uterine horns and the presence of small follicles. A score of five indicates good uterine horn size and tone, and the presence of a CL. Heifers should be tested 30 days prior to the breeding season and heifers receiving a score of less than three should be culled.

Replacement heifers should be bred approximately 21 days prior to the breeding season for the mature cow herd because first-calf heifers take longer to return to heat after calving than mature cows. The first-calf heifer must provide milk for her calf, get ready to start a new pregnancy, and still continue her own growth! The earlier breeding provides replacement heifers with a better opportunity to rebreed during the breeding season with the mature cows and potentially have an early calf the next year.

At least two weeks prior to calving, heifers should be moved to an area that is easily accessible. An ideal setup would have a small pasture near a corral that is complete with a place to pull calves, and a small pen to let heifers “pair-up” with their calves once they are born. Heifers should be checked at least three times a day during calving season.

Keep heifers separated from the older cows, and feed them better before and after calving. Heifers nursing first calves often have low conception rates or are slow to rebreed, and inadequate nutrition is often at fault. Rations should contain ample energy. Many producers turn heifers onto spring grass after they calve. While most immature grasses are of high quality, due to high moisture content, cattle must consume large quantities of grass to meet their nutritional needs. Supplementation with high-energy feeds, such as grain, is justified when grass is short or sparse.

When managing replacement heifers, remember to emphasize high fertility, early pregnancy, and ease of calving. These objectives are more important than trying to produce calves with heavy weaning weights from first-calf heifers.

Management during Calving

Death of calves at or near calving time constitutes a major economic loss for beef producers. A newborn calf represents a chance for recovering the annual cost of maintaining the beef cow and, hopefully, for realizing a profit. However, death rates in excess of 5% are not uncommon at calving time. These losses can generally be prevented by providing good management during the calving season. It is important to maintain a short calving season because good management requires frequent observation and assistance with calving when necessary. Following are some specific things you can do to increase calf survival rates.

Separate First-Calf Heifers from Mature Cows. Calving difficulty in 2-year-old heifers can run as high as 30% to 40%, whereas 3% might be a normal percentage in mature cows. It is especially important to closely observe first-calf heifers. They should be placed in a small, accessible pasture that is near a corral where assistance can be provided, if necessary.

Provide a Clean Area for Calving. A well sodded pasture or clean, dry maternity pen should be used as the calving area, never a wet, muddy lot. Calving pastures should be large enough to permit adequate exercise and should offer some protection against prevailing winds.

Be Familiar with the Signs of Calving. The earliest noticeable sign is enlargement of the udder; however, this can occur several weeks before calving. Several days before calving, the ligaments around the tailhead and in the pelvic area relax. The vulva becomes swollen and may begin to sag, discharging strings of mucus. A few hours prior to calving, most cows become nervous and uneasy. A cow will usually wander away from the rest of the herd as her contractions increase.

Check Cows Frequently. Close observation is essential for providing assistance to cows that might experience difficulty calving. Observing cows 3 or 4 times daily, and providing assistance as needed will result in more live calves. However, cows should be disturbed as little as possible during labor.

Know When Cows Need Assistance. Intervention is justified when a cow continues to have active contractions but makes no progress in expulsion of her calf. Research has shown that timely, appropriate intervention (for mature cows, 1 hour; and for first-calf heifers, up to 2 hours after the onset of abnormal contractions) increases the cow's chances of getting rebred. In a normal delivery, the calf's forelegs and head, encased by membrane, are forced through the birth canal and emerge from the vulva. You should train yourself to recognize an abnormal delivery and know when professional help is required. Using a disposable glove, feel the various parts of the calf to determine its position in the birth canal.

In normal position, the bottom of the calf's feet face downward and its head can be felt between its front legs. Some abnormalities—such as one or both forelegs back, or head turned back can be corrected by pushing the calf back and manually repositioning the extremities. Backward presentation with rear feet first is usually uncomplicated. Other abnormal positions would likely require veterinary assistance. Figure 4 illustrates some normal and abnormal presentations of the calf at parturition.

Figure 4. 

Examples of normal and abnormal presentations of the calf at parturition.

Credit: Hardin, R. 1986. Factors Affecting Calving Difficulty. Georgia Cooperative Extension Service Bulletin 943. University of Georgia, Athens.
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The following presentations require veterinary assistance:

  • Only the calf's tail is visible.

  • Only the calf's head is visible.

  • Front legs are visible past the knees, but the calf's nose cannot be located.

  • The head and only one foot are visible.

  • More than two feet are visible.

Be Sure the Calf Is Breathing Normally. Once the calf is delivered, some stimulation might be required to start its breathing. Stimulate the calf by rubbing it briskly, slapping it on the ribs, or tickling its nostrils with a straw. Mucus should be removed from the mouth and throat. Lifting a calf up by the hind legs will help drain fluids from its respiratory system.

Be Sure the Calf Consumes Colostrum. Ideally, every calf should consume colostrum (first milk) within 15 to 30 minutes following birth. A newborn calf depends upon colostrum as a source of antibodies to protect it from diseases. The sooner a calf receives colostrum, the better its protection will be. Saving and freezing colostrum, or using a commercial colostrum supplement, will help protect calves that do not nurse within 1 to 2 hours following birth.

Increase Feed after Calving. The cow's energy intake should be increased to 14 to 16 lb TDN daily as soon as the calf appears to be taking all of her milk (10 to 14 days after calving). Extra energy helps the cow produce enough milk for her calf, maintain adequate body condition, and rebreed on schedule.

Artificial Insemination

Successful artificial insemination (AI) breeding programs depend upon adequate facilities, good herd health programs, sound nutritional management and experienced, well-trained technicians responsible for detecting estrus (heat) and performing insemination. The majority of failures in AI programs are attributable to poor nutritional development in replacement heifers, inadequate body condition of cows after calving, failure to identify cows in heat, and failure to breed cows at the proper time.

Heat Detection. Accurate heat detection and record keeping are perhaps the most time-consuming and least interesting aspects of an AI program. However, in many ways they are the aspects most important to its overall success rate. Heat detection requires skilled observation, patience, and a general familiarity with the reproductive processes of cattle. Inadequate heat detection can affect herd profitability in the following ways:

  • Undetected heat results in longer calving intervals and decreased weaning weights of subsequent calves.

  • Inseminating cows that are not in heat results in decreased conception rates, and wasted time and semen (Figure 5 gives optimal breeding times).

  • Inseminating already-pregnant cows, mistakenly identified as being in heat, can result in abortion.

Figure 5. 

Best times for breeding, relative to the onset of estrus.

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Standing to be mounted is the most accurate sign heat to use when selecting cows for insemination. But because pregnant cows will on occasion exhibit signs of heat it is important to keep thorough records and to use a skilled technician.

Other physical and behavioral signs that indicate a cow may be coming into heat include the mounting of other cows, swelling of the vulva, strands of mucus discharged from the vulva, chin resting, sniffing and licking other cow's vulvas.

Cows that are isolated (or kept with sexually inactive cows) may exhibit different signs of estrus, including hyperactivity (increased movement), bellowing, tail raising and tail switching, and frequent urination. Extremes in weather, including periods of extreme cold or heat, can disrupt or diminish estrual behavior, making accurate heat detection difficult.

Accuracy of heat detection often depends upon what percentage of females are in heat at the same time. In small herds, females may come into heat one at a time, and the riding and other activity associated with heat may be limited, making heat detection more difficult. Synchronization of estrus proves to be a valuable alternative in these situations.

Heat detection can be assisted through the use of sterilized (“Gomer”) bulls, or hormone-treated steers or cows, which will readily mount cows in standing heat. “Gomer” bulls can either be penal-deviated or vasectomized. Penal-deviated bulls are surgically altered to transplant the sheath and penis from their normal position to the fold of the flank. This allows for normal erection but does not allow the bull to enter the cow. Penal-deviated bulls can learn how to breed or eventually lose interest and not try to breed. A penal-deviated bull does have less chance of transmitting venereal disease. Vasectomized bulls have been surgically altered to prevent sperm cells from being ejaculated. Vasectomized bulls will not lose interest in breeding; however, they can be transmitters of venereal disease. Chin-ball markers can be fastened on these animals to mark the backs of any cows they mount. Patches are also available. Placed on a cow's rump, the patch turns from white to red when an animal stands to be ridden by another cow or bull.

Heat detection should occur at least twice daily during the AI breeding season, early morning (just after sunrise) and late evening (just before dusk). Animals should be observed for signs of heat at least 30 minutes to one hour during each observation period. Cows should then be bred according to the AM/PM rule. The AM/PM rule consists of breeding a cow 12 hours after she has been observed in estrus (e.g., in estrus AM, breed her PM; in estrus PM, breed next AM).

HeatWatch® is an estrus detection system which utilizes computers to aid in heat detection. Small radio transmitters are placed inside a disposable patch and glued onto the tailhead of your cows (placement the same as patches described above). As mounting activity occurs, a radio receiver collects and transmits this information to a computer. The data can be presented to you by HeatWatch® software to identify animals in standing heat and animals suspected in heat. This system operates 24 hours a day, seven days a week and identifies the precise onset and duration of heat. This system best benefits beef ranchers wanting to use embryo transfer.

Semen Storage. Frozen semen is stored in ampules (glass vials) or plastic straws, which are maintained in liquid nitrogen (-320° F). The plastic, or French, straw is most commonly used. Transferring semen from one container to another must be done carefully and swiftly; the transfer should be completed within 10 seconds. Routinely check semen tanks to ensure that the level of liquid nitrogen is adequate to maintain proper storage temperature for the semen.

Semen Thawing. Frozen semen should be thawed in a warm water bath at 95° F for a minimum of 15 seconds. Since extreme water temperature can kill the sperm, it is important to annually check the accuracy of any thermometer used to measure water temperature when thawing frozen semen.

Insemination Procedure. Semen should be used within 15 minutes of thawing. Once thawed, remove the straw from its thaw bath and dry it thoroughly with a paper towel. When loading the gun, cut the straw according to the type of French gun used: either diagonally, or at a right angle to the straw. The model of French gun will also determine the type of sheath used. Protect thawed semen against temperature shock by wrapping the front end of the gun with a paper towel.

Semen Deposition. First, wipe the cow's external genitalia clean, then insert the inseminating rod into her reproductive tract. It is important to remember that the cervix should be worked over the rod; do not push the rod through the cervix. To ensure proper placement of semen in the body of the uterus, the technician should run an index finger over the front edge of the cervix to feel the tip of the gun as it protrudes into the uterus. This is illustrated in Figure 6. Insertion too far into the uterus can result in damage to the uterine lining, as illustrated in Figure 7. Research clearly demonstrates that the body of the uterus is the preferred site of semen deposition. However, on second and later services, semen should be deposited in the cervix. This is a precaution to prevent disruption of pregnancy, should a pregnant cow be mistakenly reinseminated.

Figure 6. 

The proper site for semen deposition in the cow.

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Figure 7. 

Incorrect placement of semen deposit; notice that the tip of the gun is too far into the body of the uterus.

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Estrous Synchronization

Perhaps you are not using artificial insemination because both heat detection and insemination require a lot of time and labor. Estrous synchronization allows use of AI, while reducing time and labor required for heat detection and insemination.

Synchronization alters estrous cycles so that all cycling cows come into heat during a predetermined period of time (usually the beginning of the breeding season). Synchronization allows you two chances to settle a cow or heifer in a 21- to 25-day period. Cows that breed and calve earlier wean older, heavier calves; they also have more time to rest and recycle between calving and next breeding.

Table 3 compares several available methods of heat synchronization. Today's methods support four main approaches: administration of prostaglandin, administration of Syncro-Mate B®, feeding melengestrol acetate (MGA®), and administration of prostaglandin and gonadotrophin-releasing hormone (GnRH, cystorelin®).

Prostaglandins—These include products marketed as Lutalyse®, Estrumate®, and Bovilene®, which are administered as injections to initiate new estrous cycles in cows by regressing the corpus luteum. Prostaglandins are effective on cows 6 to 17 days into their estrous cycles when the corpus luteum is present. Therefore, a cow 5 days or less into her cycle would not respond to the injection, and would require a second injection for complete synchronization. Breeding systems that use prostaglandin are illustrated in Figure 8.

Figure 8. 

Various breeding systems using prostaglandin (PGF).

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Syncro-Mate B®A treatment consisting of an ear implant and an injection, Syncro-Mate B®, requires that cattle be handled twice: to administer the injection and insert the implant, and 9 days later to remove the implant. Syncro-Mate B® is different from the prostaglandin treatment because it can initiate estrus in some heifers or cows that are not already cycling. Cows can either be inseminated after detection of heat (AM/PM rule), or (by appointment) 48 to 52 hours following removal of the implant. Removing the calf for 48 hours following implant removal is a technique used to increase conception rates in nursing cows. Breeding systems that use Syncro-Mate B® are illustrated in Figure 9.

Figure 9. 

Breeding systems using Syncro-Mate B®.

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MGA®Originally used to suppress heat in feedlot heifers by including it in their feed. Short feeding periods with MGA® combined with prostaglandin at the end of treatment can be an alternative to more expensive or labor-intensive methods of synchronizing breeding females. It is easy to use and will initiate estrus in some noncycling females.

MGA® is fed at the rate of .5 mg/head, daily for a 14-day period, in a grain mix. Cattle will exhibit heat within 48 hours following removal of MGA® from their feed, but should not be bred on that heat. Administer prostaglandin 17 days following MGA® withdrawal, and inseminate based on heat detection (AM/PM rule) (Figure 10).

Figure 10. 

Breeding system where cows are fed melengestrol acetate (MGA®) for 14 days, followed by an injection of prostaglandin (PGF).

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Prostaglandin and GnRH – Most recently developed estrous synchronization protocols are Ovsynch, Select-Synch, Hybrid Select-Synch and Co-Synch. These protocols are very similar, with their own variations, to a base protocol (Figure 11).

Figure 11. 

Various breeding using prostaglandin (PDF) and GnRH.

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Ovsynch protocol consists of using prostaglandin and GnRH and requires handling cattle three times. An injection of GnRH is given 10 days prior to the start of breeding, seven days later an injection of prostaglandin is given, and two days after the prostaglandin shot, another injection of GnRH is given. Cows can be artificially inseminated by “appointment” (timed AI) 24 hours following the second shot of GnRH. Calf removal for 48 hours is suggested at the time prostaglandin is given.

Select Synch protocol requires handling cows twice. GnRH is given on day 0 with an injection of prostaglandin given seven days later. Inseminate cows after they are detected in heat following the AM/PM rule.

Hybrid Select-Synch protocol is the same as the Select Synch protocol with the addition of a second injection of GnRH 72 hours after the shot of prostaglandin. Cows can be artificially inseminated at the time of the second GnRH injection or heat detected and inseminated following the AM/PM rule.

The Co-Synch protocol is the same as the Hybrid Select Synch protocol, with the only change being the timing of the second injection of GnRH and the timing of AI which occurs 48 hours following the shot of prostaglandin. Further work is needed to determine if the use of prostaglandin and GnRH to synchronize estrus in beef cattle will be practical and economical for beef producers. You should evaluate your situation and determine which protocol best fits your management style.

Reproduction in the Bull

Figure 12 illustrates the reproductive tract of the bull. The bull's reproductive system includes two testicles, which are housed in the scrotum. Male sex cells (sperm), which carry genetic information, are produced in the testicles. There, the sperm are contained in semen, the fluid produced by the accessory sex glands (Cowpers gland, prostate, and seminal vesicle).

Upon ejaculation, semen is discharged from each testicle through a tube called the vas deferens. The vas deferens leading from each testicle empties into the urethra. The penis is the organ of copulation and the urethra is the passageway within the penis which conducts semen and urine out its opening. One sperm from the ejected semen, carrying the male's genetic makeup, fertilizes the female's egg, which contains her genetic information.

Figure 12. 

Diagram of the bull's reproductive system.

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Breeding Soundness and Bull Fertility

Fertility of the herd bull is essential to any successful cow-calf operation. In many respects it is more of a concern than the cow's fertility, since the bull or bulls contribute at least half the genetic makeup of an entire calf crop. Subfertile bulls generate low calf crop percentages, and could also be responsible for poor herd weaning weights. Evidence shows that for every estrous cycle during which a female fails to conceive there is a corresponding 25 lb to 45 lb decrease in the subsequent calf's weaning weight. It does not take long to realize that the infertility or subfertility of a bull can be extremely costly for the cow-calf producer.

Beef bulls should be evaluated for breeding soundness 30 to 60 days prior to the scheduled breeding season. Such timely evaluation helps eliminate losses due to infertility, and affords time to replace questionable or unsatisfactory bulls. A breeding soundness evaluation (BSE) should include the following:

  • Physical examination

  • Reproductive tract examination

  • Semen evaluation

Physical Examination. A thorough physical examination should be conducted to ensure that bulls are both capable of locating cows in heat and physically capable of mating. The physical exam should include an appraisal of body condition. Thin bulls lack stamina necessary to breed with cows during a short breeding season, whereas overly fat bulls lack vigor required to breed with cows. Feet and legs should be carefully inspected to identify faults that might impair the bulls' ability to travel and mount. Structural problems (including sickle hocks, post legs, or sore feet) can impair breeding performance. Eyes should be clear, and free of disease or injury. Bulls should also be evaluated for any disease or sickness that might impair breeding performance.

Reproductive Tract Examination. A complete examination of the reproductive tract is necessary to screen for disease and abnormalities. This includes rectal palpation of the bull's internal reproductive organs. The external portion of the exam includes palpation of the spermatic cord, testes, scrotum, and epididymis. The penis and sheath should also be examined. Scrotal circumference can be easily obtained at this time. Table 4 evaluates scrotal circumference according to age. Young bulls with above-average scrotal circumference can be expected to produce more sperm cells. Research shows that 63,000,000 more sperm cells are produced per additional centimeter of scrotal circumference. Also, bulls with larger scrotal circumferences (taken as yearlings) tend to sire daughters that reach puberty at an earlier age.

Measure scrotal circumference using a flexible (centimeter) tape; slip it up and around the bottom of the scrotum. Pull the tape snugly around the widest point of the scrotum, with the testicles fully descended. Commercial measuring devices are available. However, a sewing tape can be used in an emergency. Measurements are generally given in centimeters, where 1" = 2.54 cm.

Collection and evaluation of a semen sample is advisable; this procedure can detect problems that might not be obvious in the physical exam. Usually collection is by electroejaculation or massage. Semen is then examined microscopically to evaluate sperm motility and morphology. For range-type bulls, it is recommended that semen show at least 30% motility and 70% normal sperm.

Libido and/or serving capacity tests can also be included in the evaluation, along with special tests for venereal diseases (vibriosis and trichomoniasis). Such procedures add predictive value to the assessment process. These tests may be specifically indicated in some situations; however, they are not generally part of a routine breeding soundness evaluation.

Development of Young Bulls

A primary focus when producing young bulls should be to ensure good growth rate and early development of reproductive capacity, without excessive fattening. Most bulls are sold at 1 to 2 years of age and still have a lot of growth and development ahead of them. This is particularly true of today's bulls, which are frequently selected for extra growth (and particularly Brahman bulls, which need more time to develop fully).

Most bull sales are held from August through November or December, to allow some time before the breeding season. Many of the bulls will have been fed a fairly high-concentrate diet for more than 100 days as part of a performance-testing program (or simply because buyers prefer bulls in fleshy condition). Whether a yearling bull was fed on the farm or at a test station, most were fed to gain at least 2 to 4 lb daily. After coming off test, they should continue to gain about 1.5 to 2.0 lb daily.

Very fleshy young bulls will need extra conditioning prior to breeding season; a high level of physical activity is required to breed several cows. (Bulls will get plenty of exercise if you simply place their feed and water in separate locations in a small pasture.) Bulls should be “let down” gradually, decreasing the amount of grain in their diet while increasing roughage. To keep daily gain at 1.5 to 2.0 lb, feed approximately 8 to 12 lb grain per day, in addition to spring pasture; or provide free-choice high-quality roughage along with 1.0 to 1.5 lb grain supplement per cwt body weight, daily.

At the start of breeding season, bulls should be in good physical condition, fertile, and capable of covering the necessary distances to keep pace with the cow herd (Figure 13). Overconditioned bulls will lose weight rapidly and may not be as fertile as well-conditioned bulls.

Figure 13. 

Herd bulls should be physically sound, in good flesh, and should have passed a breeding soundness evaluation prior to breeding season.

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Bulls purchased without a breeding soundness evaluation (BSE) should be evaluated prior to the start of breeding season. Older bulls (over 3 years of age) should be tested for vibriosis and trichomoniasis. Observe all bulls closely during breeding season to see if they are detecting heat and getting the cows bred. If they become too thin, it may be necessary to rest and/or hand feed them.

It is not uncommon for yearling bulls to lose as much as 100 lb or more during their first breeding season. Bulls should gain this weight back, and continue to grow so that they reach about 75% of their mature weight by the time they are 2 years old. This will require more than summer grass pasture; however, too much grain too fast can cause founder.


Table 1. 

Typical estrous cycle for the cow.

Estrous Cycle



Duration of estrus (hrs)



Ovulation (hrs after heat begins)



Length of estrous cycle (days)



Table 2. 

Estimated "target weights" for puberty in heifers.


Weight, lba













Santa Gertrudis






aWeight at which 90% of heifers will be cycling, by breed.

Table 3. 

Comparison of heat synchronization protocols in AI breeding programs.















  • 1 injection


2 times

11 days

11 days



  • 2 injectionsb+heat detection


3 times

16 days

16 days



  • 2 injections (all cows) + heat detection


3 times

5 days

5 days





Syncro-Mate B®


  • + heat detection


3 times

5 days

5 days



  • no heat detection (timed AI)d


3 times

0 days

1 day




MGA® + Prostaglandin


2 times

4 days

4 days




Prostaglandin + GnRH

  • Ovsynch (timed AI)e


3 times

0 days

1 day



  • Select-Synch


2 times

5 days

5 days



  • Hybrid Select-Synch


3 times

0 or 5 days

1 or 5 days



  • Co-Synch


3 times

0 or 5 days

1 or 5 days



aYes = Use only on cows already cycling.

bRe-inject only cows that fail to respond to first injection, but heat detect and breed following both injections.


dBreed 48-52 hours following removal of implant.

eBreed 24 hours after second injection of gonadotropin-releasing hormone (GnRH).


Table 4. 

Scrotal circumference,a by age.


Very Good



12-14 months

>34 cm

30-34 cm

<30 cm

15-20 months

>36 cm

31-36 cm

<31 cm

21-30 months

>38 cm

32-38 cm

<32 cm

31+ months

>39 cm

34-39 cm

<34 cm

a> = greater than; < = less than.

Source: Spitzer, et al. Breeding soundness evaluation on beef bulls. In: Southern Region Beef Management Handbook. ASC-121. Kentucky Cooperative Extension Service, University of Kentucky, Lexington.



This document is AN119, one of a series of the Animal Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date November 2001. Revised October 2007. Reviewed September 2012. Visit the EDIS website at


Mike Fanning, former Extension beef specialist Southwest Florida Research and Education Center; Jim Selph, county Extension director and livestock Extension agent DeSoto County; and Shep Eubanks, county Extension director and agricultural Extension agent, Holmes County, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition.

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U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.