Silage Harvesting, Storing, and Feeding
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Silage Harvesting, Storing, and Feeding

   

Silage Harvesting, Storing, and Feeding1

W. E. Kunkle, C. G. Chambliss, A. T. Adesogan, and M. B. Adjei2

Silage can be a convenient and economical feed for the cattle industry. Forages are harvested, stored, and fed as silage when field drying is not possible. Crops such as corn and sorghum reach their optimal harvest time when they contain considerable moisture. They are usually harvested as silage because their thick stalks delay drying. Bermudagrass and bahiagrass are usually harvested as hay, but frequent rains may delay harvest or cause excessive losses of dry matter (DM). Harvesting some cuttings as silage may reduce harvesting losses and allow a more timely harvest, which improves forage quality.

Silage is moist forage, stored in the absence of air and preserved by acids produced during ensiling. During ensiling, bacteria on the plant ferment plant sugars to produce organic acids (such as lactic and acetic) that lower the pH of the silage to levels that inhibit bacterial growth. The silage remains preserved as long as oxygen from air is kept out, because spoilage-causing, acid-tolerant yeasts remain dormant in the absence of oxygen. Therefore, production of excellent silage requires storage of the forage in the absence of air.

Silage has several advantages over hay, including:

Disadvantages include:

Crops for Silage

Many crops grown in Florida can be preserved as silage. The type of livestock, available machinery, soil type, rainfall, availability of irrigation, and potential yield are considerations in deciding which crops to plant.

Corn silage is usually considered the best silage because of its high energy concentration which results in good animal performance. The optimal time to harvest corn silage was previously thought to be when the grain is denting and the milk line has moved 1/2 to 2/3 of the way down the kernel (Table 1 ). This usually coincided with dry matter contents of 28 to 35%, which is near ideal for ensiling. However, the kernel milk line should no longer be the only index used to predict harvest dates. This index can give misleading predictions of optimal harvest time due to the presence of new attributes in modern corn hybrids like high stay-green and rapid drydown. Decisions on time of harvest should be based on oven dry matter measurement, and corn should be harvested for silage when the dry matter content is between 30 and 35%. Alternative, less accurate methods for measuring dry matter concentration include using a Koster moisture tester or a microwave.

Forage sorghum, sorghum-sudan hybrids, soybeans, and other warm-season annuals also make good silage, but they are lower in energy than corn silage. Forage sorghum is usually direct cut, and the moisture content at optimal maturity for harvest is often too high for proper ensiling; therefore, when choosing a hybrid to plant, pick one with a low moisture rating when possible and aim to harvest when the dry matter concentration is 30-35%. Sorghum-sudan hybrids, soybeans, and cowpeas usually have high moisture concentrations at optimal maturities (Table 1 ), and wilting is needed to ensure good silage quality.

Cool-season annuals, such as small grains and ryegrass, also make excellent silage when harvested at optimal maturities (Table 1 ) but may require wilting. Bermudagrass, stargrass, limpograss, perennial peanut, and alfalfa are often harvested as hay but can be ensiled. Ensiling these forages can be especially helpful to maintain harvesting schedules (Table 1 ) during periods of frequent rain.

Phases of Silage Fermentation

The ensiling process requires several days and can be divided into four phases. Each of the four phases is characterized by different changes in the forage.

Factors Affecting Silage Quality

Several factors are known to influence the fermentation, preservation and quality of forage that is harvested, stored, and fed as silage. These factors include sugar concentration and buffering of the forage; dry-matter concentration; chop-length and processing; temperature during ensiling and storage; rate of harvest; packing density; and air exposure during harvest, storage, and feeding.

Sugar Concentration and Buffering

Water-soluble carbohydrates (mostly sugars) are oxidized during plant respiration until oxygen (trapped during packing) is gone. These sugars constitute the primary carbohydrates that are fermented to lactic and acetic acids by bacteria to produce a low pH and stable silage. In general, forages with less than 8% water-soluble carbohydrates in the dry matter may not reach a pH low enough to produce stable, high-moisture silage. Corn, sorghum, sorghum-sudan hybrids, and cool-season annual grasses usually have sugar concentrations above 8% dry matter (Table 1 ), and a good, stable silage is often achieved. Forage crops such as warm- and cool-season perennials and soybeans and other legumes have low sugar concentrations (Table 1 ); they also have considerable buffering of pH decline in the 4.5 to 5.5 pH range. These forages often do not produce stable silage, especially when forage dry matter is less than 25%.

Dry-Matter Concentration

Harvesting should be planned for dry days as even 2 inches of rainfall can reduce silage quality. Forages that are too high or too low in dry matter may not ensile well, but for different reasons. High-moisture silage leads to greater seepage losses and possible environmental problems. Another risk of high-moisture silage is a clostridial fermentation, which leads to excessive dry-matter losses, protein degradation, high butyric acid concentrations, and unpalatable silage. Ironically butyric silages are very stable because the acid inhibits the growth of spoilage yeasts and molds, however such silages typically have poor nutritive values. Wilting of forage to 30% dry matter is a common practice that reduces clostridial fermentations. Wilting usually results in good silage in most situations when sugars are low and buffering against pH decline is high. Wilting is usually needed when bermudagrass, perennial peanut, sorghum-sudan, and millet forages are ensiled.

Forage high in dry matter presents packing problems in some chopped-silage systems such as bunker silos. Unless good packing is accomplished, air is trapped in the forage, or it penetrates from the surface, resulting in higher temperatures and poorer fermentation (see below). In situations where packing is done by mechanical means, and good packing density is achieved, air is excluded (silage in oxygen-limiting, upright silos or plastic bags), the temperatures are not elevated, and drier forages (40 to 50% dry matter) are usually preserved well.

Chop length and processing

Precision-chop forage harvesters with sharp knives should be used to achieve a chop length of ¼ -inch for unprocessed corn silage, and ¾ inch for processed corn silage. Processing ensures proper utilization of the energy in the corn kernel. Processing is advised for flint corn or hybrids with high drydown rates, high stay-green rankings, high vitreousness or hard kernels, and whenever whole kernels appeared in the feces in the previous season. Processing increases starch digestibility by about 5 percentage units leading to over 1 lb of extra milk produced per day. The roll clearance of processors should be set to 1 - 3 mm since inadequate processing is inefficient, while excessive processing can reduce fiber digestibility and predispose cows to acidosis. Processing forage sorghum hybrids before ensiling has not shown consistent benefits in research trials.

Packing density

Silage shrinkage (DM losses) increases as packing density decreases, and poor packing density can also reduce the effectiveness of silage inoculants. A target packing density of 14 lb DM/ft3 (43 lb fresh forage/cu ft) is required to minimize shrinkage. Kansas state University research shows that the optimum packing density can be achieved by aiming for a packing time of 1- 4 min/ton and using delivery rates of about 30 tons/h. Delivery rates of over 60 tons/h will lead to packing times less than 1 min /ton which can compromise packing density. High delivery rates that leave unpacked silage overnight should be avoided. A spreadsheet for properly managing bunker filling is available at www.uwex.edu/ces/crops/uwforage/storage.htm .

Temperature

The optimal temperature during fermentation is below 100°F. Higher temperatures result in poorer-quality silage even though the silage may be palatable. Temperatures above 100°F reduce the fermentation quality, enhance protein degradation, reduce the pH decline and result in heat-damaged protein. Overheated silages, frequently called "heat damaged," have a brown to dark brown color with a tobacco-type smell. Part of the protein in "heat-damaged" silages is complexed with carbohydrates and is not digestible. The concentration of heat-damaged protein depends on both the temperature (above 105°F) and the length of time it is elevated. "Heat-damaged" silage usually remains palatable, but part of the protein and some of the TDN is unavailable to livestock.

Air Exposure

Minimizing air (oxygen) exposure to silage is essential for good-quality silage. Air allows the respiration process to continue using sugars essential for acid production, which produces heat that increases temperature. Air exposure during storage leads to yeast and mold growth on and beneath exposed surfaces. Air exposure at feeding also results in rapid mold growth, heating, and reduced palatability. Bunkers and bags must be sealed on the day of harvest with 6 mil plastic to prevent subsequent spoilage and quality losses. To avoid heating and spoilage, bag and bunker plastic integrity should be examined frequently, and any holes or splits found should be immediately sealed with proper waterproof silage tape. Tires (that are touching) should be used to weigh down the plastic and exclude air from the bunker silos.

Upon opening a silo, silage at the silo face should be fed within 24 to 48 hours. Higher temperatures during the summer increase aerobic spoilage and reduce bunk life of the silage. During feeding, silage should be covered or left tightly packed until fed, at least 6 inches or more of the exposed surfaces should be removed daily ( Figure 1 ).
Figure 1. Feeding losses from this bunker silo are minimized by leaving the exposed surface tightly packed.

Additives

Many different additives can be used to alter or improve fermentation or provide nutrients needed by animals fed the silage. Forages such as corn or sorghum usually do not need additives to enhance preservation if they are harvested at proper dry matter and properly ensiled on dry days; however, additives are usually necessary to enhance the aerobic stability of such forages. Additives are also important for improving the fermentation of forages that are difficult to ensile, such as warm-season grasses and legumes.

Carbohydrate Sources

Molasses can be used to add fermentable sugars to forages low in sugars, such as warm-season grasses and legumes. Adding 40 to 100 lb molasses/ton before ensiling can increase acids produced and lower the pH, which enhances the stability in forages marginal in sugars. Other high-energy ingredients such as ground corn and citrus pulp may be added to increase the dry matter in wet forages and increase the feeding value of the silage. Molasses and other sugar or high energy sources should not be added to corn, sorghum or cool season grasses at ensiling. This is because addition of sugars to forages that already contain high sugar concentration usually increases the growth of yeasts and the incidence of spoilage.

Bacterial Inoculants

Forages usually contain 10,000 to 100,000 bacteria/gram. These bacteria are naturally occurring and ferment sugars to organic acids. Under some conditions, numbers of these naturally-occurring bacteria may be low, and these bacteria often produce a slower fermentation than commercially-available silage bacterial inoculants. Commercial homolactic (lactic acid-producing) inoculants are available from many distributors and contain selected strains of fast-growing bacteria. Homolactic inoculants containing at least 100,000 live bacteria/gram of silage can increase the rate of fermentation and result in a fermentation that produces more lactic acid, which lowers the pH faster and produces more stable silage. Such improvements are usually more common in forages with marginal sugar and dry-matter concentrations such as alfalfa and grass silages than in corn silage. Corn and sorghum silages have a high concentration of sugars and the naturally-growing bacteria that ferment the sugars, therefore homolactic bacteria do not always improve the fermentation of such forages. However after a frost or under conditions of excess moisture or dryness, such inoculants may be useful for improving the fermentation.

One of the limitations of using homolactic inoculants is that they dont reduce the incidence of aerobic spoilage when oxygen infiltrates the forage in a silo. In addition to producing lactic acid, heterolactic inoculants contain bacteria like Lactobacillus buchneri that enhance the production of the antifungal agent, acetic acid. Such inoculants are therefore usually effective at reducing the growth of yeasts and molds and increasing silage aerobic stability.

Novel 'combo' inoculants which contain both homolactic and heterolactic L. buchneri bacteria aim to enhance the both the fermentation process and aerobic stability. Recent studies have confirmed their effectiveness on corn silage and bermudagrass silage.

Enzymes

Forages with marginal concentrations of sugars may benefit from enzymes that can break down complex plant carbohydrates to simple sugars, which then can be fermented to lactic acid. Enzymes such as amylases, cellulases, and pectinases can break down starch, cellulose, and pectin, respectively, in the forages. Most enzymes commercially available are mixtures of several enzymes produced from Bacillus and Aspergillus organisms. Although adding enzymes to forages that are difficult to ensile holds promise, most of the enzyme products available have not been adequately tested to determine their effects on many Florida forages. Recent studies at the Department of Animal Sciences showed only one of four commercial enzymes that were tested reduced DM losses and protein degradation, and improved the digestibility, fermentation and stability of bermudagrass silage. The same enzyme increased the energy balance in dairy cows and improved the efficiency of nitrogen use.

Nitrogen Sources

Ammonia and urea are sources of nonprotein nitrogen used to increase the crude protein concentrations of corn, forage sorghum, and other silages that are low in protein. Adding 5 to 10 lb of anhydrous ammonia/ton or 10 to 20 lb of urea/ton can increase crude protein concentration by 3 to 7 percentage units in the silage dry matter. Higher levels of ammonia should not be applied to silage because of the risk of formation of a compound that is toxic to cattle. Ammonia also inhibits growth of molds, and ammonia-treated silages have less heating and a longer bunk life when fed to livestock. Ammonia can be added at the chopper, blower, or bagger depending on the situation. A major drawback of ammonia is its volatility, corrosion to equipment, and operator risks associated with this volatile chemical.

Acids

Research indicates that adding acids such as sulfuric, formic, and other strong acids decreases the pH of forage and helps preserve it, but the corrosiveness and cost of these acids has discouraged widespread use. Propionic acid is a mold inhibitor that has been added to forages preserved as silage. Propionic acid reduces molding, heating, and aerobic deterioration, which is more important in surface layers. Propionic acid is relatively expensive, and use is often limited to the last few loads of silage at the top of conventional or bunker silos, where it is added to reduce surface spoilage. Several new buffered acid products are now commercially available and these are less corrosive or hazardous than the acids, and often effective at improving the fermentation or preservation of silage.

Systems

Silos used to store forage for ensiling include large tower silos, horizontal bunkers and stacks on the ground, chopped silage in long plastic bags, and round bales stored in bags, tubes, stacks of bales under plastic, or individually "stretch wrapped." Tower or upright silos have not been popular in Florida due to the high initial capital investment. Chopped silages have been stored in many different types of horizontal silos in Florida. In recent years, round-bale silage has gained popularity for producers using smaller quantities of silage.

Chopped Silage

This system requires specialized equipment, including a chopper, wagons or trucks for hauling, a silo, and tractors or other power units for the equipment. The cost of equipment for this system is often $50,000 or more; so producers using chopped silage typically harvest 1,000 tons or more each year if they own the equipment or hire custom operators to harvest smaller quantities. In most situations, forage should be chopped to 0.5 inches or less in length. Fine chopping allows better packing, better elimination of air, less separation, and better digestibility. The chopper knives and the shear bar need to be sharp and properly adjusted to consistently achieve the desired length of chop.

Upright silos (top-unloading and bottom-unloading) offer vertical pressure for good packing and have less silage surface exposed to air. These silos are well suited for storing up to a few hundred tons of silage, and the initial capital costs may be returned by reduced silage dry-matter losses after several years of use. Storage losses under 10% of dry matter harvested have been reported in some studies.

Bunker, trench, and stack silos ( Figure 2 ) offer horizontal storage for chopped forage with less investment per ton of stored silage and are widely used for large quantities. These silos usually have higher dry matter losses during storage and feeding than tower silos. Dry matter losses as low as 15 to 25% are possible, but losses above 30% have been reported. Dry matter losses can be reduced by chopping finely, packing well, filling rapidly, harvesting at optimal moisture, making deep piles, covering the surface with a plastic sheet, and feeding at least 6 inches/day from the exposed surface. Good packing and covering of surfaces with plastic held down by tires can significantly reduce air exposure and spoilage ( Figure 3 ). Silages above 35% dry matter may need to have water added when stored in horizontal silos to avoid packing difficulties. Horizontal silos are best suited for corn and sorghum silages where large quantities are harvested in one cutting.

Figure 2. Storage and feeding losses exceed 25% for uncovered stacks of silage.
Figure 3. Covering a bunker silo with plastic reduces surface spoilage.

Silage in plastic bags is made with machines that pack chopped silage into long plastic tubes. Bags from 100 feet to over 200 feet can store 0.75 to 2 tons/foot of length. The plastic bag is not reusable and typically costs $3 to $5/ton of silage stored. The system limits air exposure, heating, and spoilage and is well suited for forages that need to be wilted for good preservation. The bags can be located near feeding areas, and head gates are available for feeding silage from the bag without handling the silage again ( Figure 4 ). This storage system works well when smaller quantities of forages are harvested several times, i.e., warm-season perennial grasses.
Figure 4. Cattle can be self-fed from plastic bag silos using an easily built head gate and an electric-fence charger.

Round-Bale Silage

Forage with higher moisture content than hay can be baled similarly to hay, and air can be excluded by storing them in plastic bags ( Figure 5 ), tubes, stacks ( Figure 6 ), or bales individually wrapped with "stretch-wrap" plastic ( Figure 7 ). This system requires lower capital investment than chopped-silage systems for those producers who already have hay-harvesting equipment. The "stretch-wrap" plastic system is becoming more widely used for hay-type crops in Florida. The "stretch-wrap" machine costs $5,000 to $15,000 depending on the features of the machine, and the plastic costs $2 to $3/bale or $10 to $12/ton of dry matter. This system has worked well for cattlemen harvesting warm-season perennials as hay when the weather permits and as round-bale silage during rainy periods.

Figure 5. Round-bale silage stored in individual bags should be double tied.
Figure 6. Round bales can be ensiled by stacking, covering with sunlight-resistant plastic, and sealing with dirt.
Figure 7. Round-bale silage stored in "stretch wrap" is becoming more popular in Florida.

Research and experiences by cattlemen using round-bale silage indicate it is important to wilt forages such as bermudagrass to 30 to 40% dry matter before baling. Wilting increases forage dry matter in each bale and improves cattle gains. Wilting also decreases bale weights and reduces number of bales/acre, wrapping costs, and storage losses. Holes in plastic allowing air to enter and spoilage to occur have been a problem in some situations. Holes have been attributed to poor plastic quality and punctures. Ultraviolet light from sunlight exposure can cause "stretch wrap" and other plastics to lose flexibility and break; therefore, selecting good-quality plastic is essential. Punctures of plastic from falling tree limbs, wildlife, cattle, rodents and equipment can result in spoilage, and some of these failures can be avoided by proper handling and selection of storage areas.

Tables

Table 1. Guidelines for harvesting and managing forages harvested as silage.

Crop

Stage of Harvest

Yield potential tons DM/acre

/year

Dry matter at harvest, %

WSCHOa % DM

Management suggestions

1st Harvest

Additional harvests
Warm-season annuals
Corn


 Dry matter content of 30-35%

--

4-8

28-35

10-20

 Direct cut
Forage sorghum


 Boot or soft dough

--

3-8/harvest

20-35

10-20

 Select varieties with higher dry matter at harvest (>30% DM)
Sudan, sorghum-sudan, millet


 36" height to boot

36" height to boot

2-4/harvest

15-30

10-15

 Wilt if <25% DM
Soybeans


 Pre-pod to bean fill, before leaf drop

Usually 1 harvest

1-3

25-40

2-4

 Wilt if <30% DM
Cowpea


 Pre-pod to pea fill

Usually 1 harvest

1-3

15-30

5-8

 Wilt if <30% DM
Cool-season annuals
Rye, oats, wheat, triticale


 Boot to soft dough

--

2-4

20-30

8-12

 Wilt if <25% DM
Ryegrass


 Boot to heading

Every 30 days

2-4

15-30

8-12

 Wilt if <25% DM
Warm-season perennials
Bermudagrass, stargrass


 Pre-head (12-15" tall)

Every 4-5 weeks

6-10

18-30

2-4

 Wilt if <30% DM
Bahiagrass


 Pre-head

Every 4-5 weeks

3-5

20-30

<5

 Wilt if <30% DM
Limpograss


 12-15" tall

Every 5-7 weeks

4-8

20-30

<5

 Wilt if <30% DM
Perennial peanut


 8-12" tall

Every 5-7 weeks

2-4

18-30

1-4

 Wilt if <30% DM
Cool-season perennial
Alfalfa


 Bud to 10% flower

Bud to 10% flower

4-6

22-35

4-7

 Wilt if <30% DM
aWater-soluble carbohydrates-sugars fermented to lactic and other acids during ensiling.

Footnotes

1. This document is SS-AGR-177, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First Published July 2002. Revised April 2006. This publication is also part of the Florida Forage Handbook, an electronic publication of the Agronomy Department. For more information you may contact M.B. Adjei (mba@ufl.edu). Please visit the EDIS Web site at http://edis.ifas.ufl.edu.

2. W. E. Kunkle (deceased), professor, Animal Science Department; C. G. Chambliss (deceased), associate professor, Agronomy Department; A. T. Adesogan, associate professor, Animal Sciences Department; M. B. Adjei, associate professor, Agronomy Department, Range Cattle Research and Education Center--Ona, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 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.

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. Larry Arrington, Dean.


Copyright Information

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