Feeding and Nutrition

Chapter 2 Feeding and Nutrition



Darrell L. Rankins, Jr. , D.G. Pugh


More than any other factor identified in veterinary management of sheep and goats, diet has a profound effect on general health of both the individual animal and the flock or herd. The diet will have an impact on all aspects of animal health and productivity and therefore is discussed in almost every chapter in this book. The goal in feeding sheep and goats is optimal health as reflected in productivity, reproduction, and performance.


Sheep and goats are able to optimally convert browse, forages, and other feedstuffs barely usable for more commonly encountered livestock species into usable animal products (e.g., meat, milk, fiber) or to reach peak performance (e.g., pet, show, breeding). These two small ruminant species exhibit a high degree of mobility of the lips and tongue, which allows selective consumption in the diet, choosing from among plants and other foodstuffs available in the environment. Like other ruminants, both sheep and goats can be characterized by their grazing preferences.1 Sheep are grass or roughage grazers and tend to graze higher-quality portions of the plant. Goats, as active foragers, tend to select highly digestible portions of grasses. They also can use browse that is woody or stemmy and will readily consume flowers, fruits, and leaves; they generally select grass over legumes and browse over grass; and they prefer to graze along fence lines and in rough or rocky pasture areas. Goats typically perform poorly compared with sheep or cattle on flat, improved, monoculture pastures but usually flourish in areas featuring browse or numerous plant species to graze. If given a choice, many meat goats (e.g., Kiko, Spanish, Boer, Tennessee Wooden Leg) prefer a diet of 15% to 20% grasses and 80% to 85% browse.1


Goats are extremely particular about their diet and refuse to consume feeds that have been soiled but are used for brush management in many regions of the world. Goats maintained for brush control should be closely monitored for changes in body weight, body condition score (BCS), and hair coat; the clinician also should look for any signs of toxicosis. Whenever browse, with its deeper root systems, is the predominant forage consumed, mineral uptake may be greater than that expected with consumption of grasses grown on the same land. Both sheep and goats also are excellent converters of browse and brush to meat, fiber, and milk, but they are raised mostly as grazing animals.1



Water


Although often taken for granted, water is an extremely important nutrient. It is the major constituent of an animal’s body. If an animal were deprived of all nutrients, it would succumb to water deprivation first. Although sheep and goats may survive despite loss of most of their body fat and up to 40% to 50% of their total body protein, a water loss of only 10% can prove fatal.


Both sheep and goats are particular about the quality of their water sources. A fresh, clean, non-stagnant source of water should be available at all times. Water sources should be easily accessible, safe, and should be monitored so they are not a source of toxins and/or pathogenic organisms. A paved surface 8 to 10 feet around the water tanks/troughs helps prevent unsanitary conditions conducive to many diseases, including footrot.


Daily water intake can be affected by several factors. Pregnancy and lactation increase water requirements and consumption—water intake is increased 126% from months 1 to 5 of gestation. In addition, water intake is greater for females carrying twins than for those carrying only a single.2 Likewise, lactating ewes or does consume twice as much water as that typical for nonlactating females: 7 to 15 L/day versus 3.5 to 7 L/day, respectively. Animals grazing lush spring pastures, for which the forage water content may exceed 80%, consume markedly less water than those restricted to dry hay, which may be only 12% to 15% water. Obviously, lactating dairy animals require even greater quantities of water. When high-protein diets are being fed or when mineral consumption increases, water consumption also increases. Sheep may increase their water intake 12-fold during summer over that during the winter months.2 Water quality also can affect daily water consumption. For maintenance, individual goats and sheep usually consume 3.5 to 15 L of water/day.3


Water varies in quality according to the amount and type of contaminant. The most common dissolved substances in water are calcium, magnesium, sodium chloride, sulfate, and bicarbonate.3 If the salts of these minerals are present in high-enough concentrations, depressed performance, illness, and occasionally death can result. In addition to causing various specific problems in animals, dissolved salts have additive effects on suppression of production and health. As salt concentrations increase, water consumption usually is depressed, with young animals generally being more affected than adults. Over time, animals tend to adapt to water with high concentrations of dissolved salts. Rapid or abrupt changes from water with relatively low concentrations to water with high concentrations of dissolved substances are poorly tolerated, however.3–6 High sulfate concentrations in the range of 3500 to 5000 parts per million (ppm) may result in suppressed copper absorption from the intestine. Nitrates and, less commonly, nitrites occasionally are encountered in toxic concentrations from ground water. Most safe, drinkable water has a pH of 7 to 8. As the alkalinity of water increases, its suitability for consumption decreases.


Although water contaminated with coliform bacteria has been associated with disease in humans, only rarely is coliform contamination of drinking water implicated as an agent of disease in sheep and goats. In general, only very young animals are affected. Goats tend to adapt to high ambient temperatures better than do other domestic ruminants and require less water evaporation to control body temperature.7 In addition, they possess the ability to reduce urine and fecal water losses during times of water deprivation.


In summary, sheep and goats should have access to a continuous supply of fresh, clean water, to ensure that productivity is not compromised.



Energy


Energy generally is the first limiting nutrient under most practical conditions where sheep and goats are maintained throughout the world. Energy requirements vary greatly depending on level and stage of production, level of activity, and intended animal use. Except in situations in which rapid growth rates are desired or milk production is to be maximized, the energy requirement usually can be met with medium- to high-quality forage. Under maximal production pressures, however, some sort of supplementation may be required. Energy-deficient diets can result in poor growth rates, lower BCSs, decreased fiber production, reduced fiber diameter, decreased immune function, and increased susceptibility to parasitic diseases and other pathologic conditions. Angora goats and many wool breeds of sheep are prone to various fiber production changes, whereas cashmere goats may be less susceptible.


The greater part of the energy that is used by sheep and goats comes from the breakdown of structural carbohydrates from roughage. Therefore roughage should constitute the bulk of their diet. Energy can be expressed in terms of the net energy system (calories) or in terms of total digestible nutrients (TDN) as a percentage of the feed. The two expressions are interchangeable with use of various prediction equations; in this chapter, TDN is used as the measure. Currently, most feed and forage testing laboratories estimate TDN using the Van Soest fiber analysis. A representative sample is analyzed for neutral and acid detergent fiber contents, and then TDN is predicted based on one or both of these values. This system works effectively for most forages but is less reliable for feeds that are high in starch (e.g., corn). In general, warm-season, perennial grass hays are approximately 50% to 54% TDN, whereas many of the cereal grains usually are 80% to 90% TDN. Most forages in the green, vegetative state are approximately 62% to 70% TDN on a dry matter basis. Stemmy, dry, poor-quality hay is less than 50% TDN. By comparing these typical values with the requirements of various classes of sheep and goats, keepers can ascertain when supplemental energy sources are needed for forage-based rations. For example, a 150-lb ewe requires a diet containing 52.5% TDN for maintenance and 66% for the first few weeks of lactation, with a steady increase from 53% to 66% TDN during gestation. Therefore the dry (nonlactating), nonpregnant ewe could use low-quality forage, but the pregnant or lactating ewe needs a diet of lush, vegetative forage. If a good to excellent forage is unavailable, some type of energy supplement is required for the ewe in late pregnancy or while lactating. Similar supplementation may be indicated for goats: A 110-lb doe requires a diet containing 53% TDN for maintenance but higher amounts during pregnancy and lactation.2


A variety of choices are available for energy supplementation. The most common choice is cereal grains, corn being the most common of these. Corn is dense in energy, and most of that energy is in the form of starch. When appreciable levels of starch are supplemented to ruminants consuming forage-based diets, the general response is a decrease in forage intake and digestibility. However, the energy status in the sheep or goat receiving corn supplementation will still be improved because of the energy from the corn. Several other cereal grains are available for use as energy supplements for ruminants consuming forage-based diets (e.g., grain sorghum, oats, barley, rye). Two other nontraditional energy supplements are soybean hulls and wheat middlings. Soybean hulls are the outermost layer of the soybean and are composed of abundant quantities of digestible fiber. Unlike corn, soybean hulls do not suppress fiber digestion but may increase hay digestibility. Even though soybean hulls have a TDN value 62% less than corn, they produce similar results when used as an energy supplement for ruminants consuming forages. Wheat middlings, a byproduct of wheat milling, elicit similar responses. Beet pulp, citrus pulp, and brewer’s grains all are byproduct feedstuffs that can be effectively used in both sheep and goat feeding, and these byproduct-type feeds often are much more economical than corn. All byproduct feeds should be analyzed for composition and used accordingly in diet formulation.


Another source of energy supplementation is fat. In general, total fat content should not exceed 8% of the diet, or 4% to 5% as supplemental fat. In the southern United States, where cotton production is prevalent, whole cottonseed (which contains approximately 24% fat) is used as an energy supplement for both sheep and goats. In animals of both species, the diet should be supplemented with no more than 20% of the daily intake as whole cottonseed, assuming that the remainder of the diet contains no fat.



Protein


As a general rule, a minimum of 7% dietary crude protein is needed for normal rumen bacterial growth and function for sheep and goats. If dietary protein drops below 7%, forage intake and digestibility are depressed. Protein deficiency is associated with decreased fiber production, slowed growth, decreased immune function, anemia, depressed feed use, edema, and death. All of the protein reaching the small intestine is found in bacteria or protozoa or dietary protein that escaped ruminal digestion. The quality (amino acid content) of the bacterial protein is surprisingly quite good. Therefore the quantity of dietary protein provided to adult ruminants is much more important than the quality. The opposite is true of the preruminant lamb or kid. If lambs or kids are fed a milk replacer, it should be composed of milk byproducts to provide an adequate amino acid composition for maximal growth.


Crude protein content varies widely among the various feedstuffs. Warm-season, perennial grass hay samples can range from less than 6% to more than 12% crude protein, whereas legumes in the vegetative state may occasionally be more than 28% crude protein. The protein content of plants declines with maturity. As with energy needs, crude protein requirements vary with the animal’s stage of production. For maintenance, ewes and does of most weight classes require a diet containing 7% to 8% protein. During lactation, both ewe and doe require 13% to 15% crude protein in the diet, depending on the number of offspring suckling. Supplementation of protein may be necessary for heavy-producing animals. Whenever grass hay is fed, protein deficiency should be a concern, particularly for growing or lactating animals. The most consistent sign of protein deficiency in lactating animals is poor weight gain or slow growth in their lambs or kids, particularly with twins or triplets.2


Typical protein supplements include the oilseed meals (cottonseed meal, soybean meal), commercially blended supplements containing both natural protein and nonprotein nitrogen (NPN) (e.g., as range cubes or pellets or molasses-based products), and various byproducts (whole cottonseed, corn gluten feed, dried distiller’s grains). Protein should be fed to meet, but not greatly exceed, requirements. Excess protein usually results in increased feed costs and higher rates of disease (e.g., heat stress, pizzle rot).


Giving NPN is an inexpensive way to increase the protein concentration of rations for sheep or goats. NPN is any source of nitrogen in the nonprotein form, but the most commonly used type is urea. Whenever NPN is used, the diet should have sufficient amounts of highly fermentable energy components. Feeding grain with NPN can result in a decrease in rumen pH. In this altered environment, the ability of the ruminal urease enzyme to ferment urea is depressed, resulting in a slower release of or breakdown to ammonia and carbon dioxide (CO2). Slowing this metabolic pathway allows more efficient protein synthesis by the rumen microbes. By contrast, diets of poor-quality roughage result in a higher rumen pH and enhanced urease activity. These conditions result in a quicker release of ammonia, a poorer “marriage” of chains of carbon atoms and nitrogen for microbial protein synthesis, and a potential increase in the incidence of urea or ammonia toxicity. Whenever NPN is added to the diet, feeds containing a urease enzyme should be limited or avoided. Such urease-containing feeds include raw soybeans and wild mustard. Signs of urea or ammonia toxicity, which may be fatal, include dull or depressed demeanor, muscle tremors, frequent urination and defecation, excessive salivation, increased respiration, ataxia, and tetanic spasms. Treatment includes the infusion of a 5% acetic acid solution (vinegar and water) into the rumen through a stomach tube. In severe cases, rumenotomy and fluid therapy may be required.


The following guidelines are useful when urea is fed as a protein source:



1. Never use urea for more than one third of the protein in the diet or more than 3% of the grain portion of the diet.


2. Ensure that a highly fermentable source of carbohydrates (e.g., corn, milo) is fed along with NPN.


3. Avoid the sudden introduction of urea into the diet (allow at least 8 to 10 days for its introduction).


4. Ensure proper mixing of feedstuffs whenever urea is used.


5. If 1 lb of urea plus 6 lb of ground corn is cheaper than 7 lb of cottonseed meal or soybean meal, then the former diet may be efficiently fed. However, if 7 lb of either the cottonseed or the soybean meal is less expensive, the urea should be avoided.


6. If the crude protein of the diet is greater than 14% of the dietary TDN, NPN is of little value. For example, if TDN is 45%, which is typical of many dry hays during winter, NPN is of limited or no value if the crude protein of the diet is greater than 6.3% (45 × 0.14 = 6.3).


Because of variable dietary intake and its relationship to body condition scoring, NPN is best used in sheep or goats with BCSs greater than 2.5; they should be avoided in animals with a BCS of less than 2. If NPN is offered to animals, it should be fed daily; less is used for protein synthesis if the supplement is fed less frequently. In one report, the inclusion of NPN in poorly digestible forage diets for lambs resulted in increased weight gain and wool production and decreased signs of parasitic nematode infestation.8



Minerals


Clinicians generally consider seven macrominerals and eight microminerals when assessing mineral nutrition for sheep and goats. The designations macro and micro do not reflect the minerals’ relative importance but rather characterize the amount of each that is required as a proportion of the diet. Macromineral needs usually are expressed as percentage of the diet, whereas micromineral needs generally are expressed as ppm or mg/kg.


The seven commonly assessed macrominerals are calcium, phosphorus, sodium, chlorine, magnesium, potassium, and sulfur. The eight microminerals are copper, molybdenum, cobalt, iron, iodine, zinc, manganese, and selenium. Trace mineral deficiency is less common than energy, protein, or macromineral deficiency. Such deficiencies evolve slowly over time and rarely lead to the dramatic effects on productivity and body condition seen in protein deficiency.2 In some cases of mineral deficiency, liver biopsy is the diagnostic tool of choice. The technique for liver biopsy is covered in Chapter 5.



Calcium and Phosphorus


Calcium and phosphorus are interrelated in body functions and are therefore discussed together. Nearly all of the calcium in the body and most of the phosphorus is found in the skeletal tissues. Diets deficient in calcium and phosphorus may delay growth and development in young lambs and kids and predispose them to metabolic bone disease (e.g., rickets, osteochondrosis) (see Chapter 11). Likewise, calcium and phosphorus deficiencies in lactating ewes and does can dramatically reduce milk production.


Serum phosphorus concentrations are not highly regulated but are still maintained between 4 and 7 mg/dL for sheep and between 4 and 9.5 mg/dL for goats. Phosphorus deficiency is the most commonly encountered mineral deficiency in range- or winter-pastured animals. Most forage tends to be high in calcium and relatively low in phosphorus; this is true especially for legumes. Beet pulp and legumes (such as clover and alfalfa) are good to excellent sources of calcium. For lactating dairy goats and sheep, supplemental calcium and phosphorus are necessary to meet high demands for milk production. Range goats may need less supplemental phosphorus than sheep because of their preference for browse and plants that tend to accumulate phosphorus. Phosphorus serum concentrations of less than 4 mg/dL may indicate phosphorus deficiency.2 Phosphorus deficiency results in slow growth, listlessness, an “unkempt” appearance, depressed fertility, and depraved appetite or pica.2


Sheep and goats fed high-grain or high-concentrate diets typically need supplemental calcium and little to no additional phosphorus. Grains are relatively low in calcium but contain moderate to high concentrations of phosphorus. Although serum calcium is tightly held in a narrow range, serum concentrations consistently below 9 mg/dl are suggestive of chronic calcium deficiency.2 Chronic parasitism can lead to decrease in body stores of both calcium and phosphorus.2 Common calcium supplements include oyster shells and limestone. Defluorinated rock phosphate is an excellent source of phosphorus. Dicalcium phosphate or steamed bone meal (when available) are good sources for both. The calcium-to-phosphorus ratio should be maintained between 1:1 and 2:1.2



Sodium and Chlorine


Sodium and chlorine are integral components of many bodily functions. Salt (sodium chloride [NaCl]) is the carrier for most ad libitum mineral supplements. If salt is not offered ad libitum, it should be incorporated into a complete ration at a level of 0.5% of the diet. Sodium is predominantly an extracellular ion and is important for normal water metabolism, intracellular and extracellular function, and acid-base balance. Conversely, chloride is an intracellular ion, functions in normal osmotic balance, and is a component of gastric secretions. Sheep or goats that are deficient in salt intake routinely chew wood, lick the soil, or consume other unlikely plants or debris. The NaCl content of feeds may be increased to 5%, particularly for feeding males, to help increase water intake and reduce the incidence of urolithiasis (see Chapter 12).


Salt commonly is used as a carrier to ensure trace mineral intake, because sheep and goats have a natural drive for NaCl in the diet. An important consideration in the decision to use a salt-containing mineral mixture to ensure mineral intake is that individual consumption may vary drastically. Furthermore, improperly prepared salt mixtures or blocks, feed supplements, liquid feeds, or certain types of food or water contamination may be associated with drastically altered mineral consumption.


Salt also is useful as an intake limiter for energy-protein supplements. A 10% to 15% NaCl mixture of two parts ground corn and one part soybean meal is approximately 20% crude protein. The added salt usually limits intake of this mixture to 0.45 kg/day in the adult goat or sheep. Whenever using salt-limited feeding, the keeper should take care to introduce the feedstuffs slowly over 2 to 3 weeks and provide access to adequate quantities of fresh clean water. Only white salt should be used as an intake limiter. If trace mineral salt or ionized salt is used, mineral (e.g., copper, iodine) toxicity is likely, particularly in sheep.



Magnesium


Magnesium is important for normal functioning of the nervous system and is required for many enzymatic reactions. Skeletal magnesium can be used by the animal during times of deficiency, but the skeletal magnesium reserve is much smaller than the calcium reserve. Many fast-growing–heavily-fertilized-cereal grains or grass pastures are deficient in magnesium. Magnesium absorption is depressed by high concentrations of plant potassium or rumen ammonia. Legume and legume-grass mixed pastures are good sources of magnesium. A magnesium deficiency can lead to a clinical manifestation known as grass tetany in either sheep or goats. Magnesium toxicity is very rare.



Potassium


Potassium is required for normal acid-base balance and is an integral component of many enzymatic pathways; it functions as an intracellular ion. The requirement is between 0.5% and 0.8% of the diet, depending on the stage of production. Most grains contain less than 0.4% potassium, whereas fresh green forages generally contain more than 1%. Dormant forages, however, may have much lower potassium concentrations.


Potassium deficiency or toxicity is rare in sheep and goats. However, deficiency may occur in highly stressed animals being fed diets composed mostly of grain. Therefore, in stressful situations (such as weaning), supplemental potassium may be indicated for animals fed predominantly on grain.2



Sulfur


Sulfur is a component of many bodily proteins. It is found in high concentrations in wool and mohair, in keeping with the large amounts of sulfur-containing amino acids (cystine, cysteine, and methionine) in keratin. Sulfur deficiency can reduce mohair production in Angora goats.9 The general recommendation is to maintain a 10:1 nitrogen-to-sulfur ratio in sheep and goat diets.2 Ideal ratios of 10.4:1 for maximal gains and 9.5:1 for maximal intake in growing goats.10 However, a ratio as low as 7.2:1 has been suggested for optimal mohair production.11 If the forage has a low sulfur content or if large quantities of urea are used in the diet, weight gain and fiber production can be increased by providing supplemental sulfur.


In both sheep and goats, sulfur deficiency may result in anorexia, reduced weight gain, decreased milk production, decreased wool growth, excessive tearing, excessive salivation, and, eventually, death. Browsing animals such as goats may ingest enough tannins to decrease sulfur availability. Sulfur deficiency also depresses digestion, decreases microbial protein synthesis, decreases use of NPN, and lowers the rumen microbial population. Whenever NPN is fed to fiber-producing animals, sulfur supplementation is indicated. With the possible exception of oats and barley, the sulfur content of most cereal grains usually is low to deficient, although corn-soybean diets usually meet requirements for the ruminal synthesis of sulfur-containing amino acids.


Sulfur toxicity occasionally is seen in settings in which calcium sulfate is used as a feed intake limiter. It also occurs when ammonium sulfate is fed as a source of NPN or as a urinary acidifier. If sulfur is supplemented in the form of sulfate, toxicity may occur, particularly if the sulfur content is greater than 0.4% of the diet.2 Sulfate can be reduced to sulfide in the rumen or lower bowel. Sulfide in large enough concentrations can result in polioencephalomalacia that is only partially responsive to thiamine (see Chapter 13).


In the southeastern United States, use of ammonium sulfate as fertilizer has increased appreciably with the rising cost of commercial nitrogen. If signs of marginal trace mineral deficiencies begin to appear in any group of sheep or goats, forage sulfur concentrations should be measured. An excess of dietary sulfur can lead to deficiency of any of several trace minerals (e.g., copper, zinc) without causing any overt toxicity problems.



Copper


Copper deficiencies can be primary (as a result of low intake) or secondary (caused by high concentrations of molybdenum, sulfur and/or iron, or other substances in feedstuffs). In the rumen, copper, molybdenum, and sulfur form thiomolybdates, which reduce copper availability. Specifically, copper’s ability to function as part of the enzyme systems needed for specific biochemical reactions is depressed. This impairment in metabolism results in clinical signs of deficiency. Other factors that alter copper absorption include high concentrations of dietary cadmium, iron, selenium, zinc, and vitamin C as well as alkaline soils. Zinc supplementation in the diet (to a concentration higher than 100 ppm) will reduce availability and liver stores of copper. Roughage grown on “improved” (fertilized, limed) pastures is more likely to be deficient. Liming reduces copper uptake by plants, and many fertilizers contain molybdenum. Good-quality lush grass forages have less available copper than that typical for most hays, and legumes have more available copper than most grasses. Liver copper reserves last up to 6 months in sheep.2



Copper Deficiency


Signs of copper deficiency include microcytic anemia, depressed milk production, lighter or faded-looking hair color, poor-quality fleeces, heart failure, infertility, increased susceptibility to disease, slowed growth, enlarged joints, lameness, gastric ulcers, and diarrhea. These signs appear to be more severe with primary copper deficiencies than with a lowered copper-molybdenum ratio. Sheep with copper deficiency have inferior wool, which usually is characterized as “stringy” or “steely.” Such wool lacks both tensile strength and crimp. Growing lambs and kids are most susceptible to copper deficiency, followed by, in order of predisposition, lactating females.


Several breed differences have been observed with regard to copper metabolism. For example, some Finnish-Landrace sheep may have lower serum copper concentrations than in Merinos, which in turn have lower serum copper levels than in British breeds at similar levels of intake.12 Milk usually is deficient in copper, whereas molybdenum is concentrated. In lambs suspected of having “swayback,” liver copper concentrations usually are less than 80 ppm dry weight.


Anecdotal reports indicate that goats offered only sheep mineral (with low to absent added copper but with added molybdenum) may succumb to copper deficiency. The risk of this deficiency may be magnified in pygmy goats and young, growing animals. Merino sheep and dwarf goat breeds require 1 to 2 ppm more copper than other breeds. Copper is absorbed more efficiently by young animals than by adults.2 Copper supplementation appears to have some effect on the control of nematode parasites.


Very young lambs or kids can present with enzootic ataxia. Affected animals are born from copper-deficient ewes or does. The swayback condition of lambs or kids usually is seen at birth but may be diagnosed in animals up to 3 months of age. Neonates may experience a progressive ascending paralysis. Manifestations of this ataxia include muscular incoordination (especially in the hindlegs) and failure to nurse. Most neonates die within 3 to 4 days of onset of the first clinical signs and symptoms. Affected older animals may survive or die, depending on severity. Rear limb ataxia, muscle atrophy, and weakness are noted in lambs or kids from 2 weeks to 3 months of age.


A definitive diagnosis is made with necropsy. Histopathologic examination of the spinal cord reveals myelin degeneration and cavitations of cerebral white matter. Liver copper concentrations are invariably depressed. Prevention and treatment consist of copper supplementation (using oral supplements, copper needles, a trace mineral mixture, or injectable copper) and maintaining an appropriate dietary copper-to-molybdenum ratio (see Chapter 13).


If copper deficiency is suspected, the copper, molybdenum, sulfur, and iron concentrations of the diet should be determined. To confirm copper deficiency, the nutritionist or clinician should measure body tissue concentration. Serum copper commonly is used to determine body copper status, but much of the copper is bound in the clot, making plasma a more reliable indicator of body copper status. Unfortunately, from a body assessment standpoint, blood copper concentrations may be falsely increased by stress or disease. If serum copper is overtly low and animals were not stressed during sampling, copper deficiency is likely. If serum copper concentrations are used for assessment, and copper concentrations fall within normal ranges, additional copper supplementation is of little or no value. An exception is those cases in which serum copper is normal but dietary molybdenum is high, or the copper-to-molybdenum ratio is less than 4:1. In such cases the assayed copper may not be available for use in body metabolism. The dietary copper-to-molybdenum ratio should be maintained between 5:1 and 10:1. Liver is the best tissue to use in determining body copper status, but among other limitations, it is a poor indicator of short-term copper balance. If liver copper is marginal, but plasma or serum copper is in the normal range, the animal may have a favorable response to copper supplementation. In such instances, dietary copper probably is deficient, and the liver stores of copper are being depleted. If a herd problem seems likely, the clinician should sample not only a cross-section of ages and production status but also as many symptomatic animals as possible.


Forage samples should be taken for copper and trace mineral analysis. Core samples of hay should be properly collected. Feed samples should be placed in plastic bags, not brown paper boxes or bags. Dietary copper should range between 4 and 15 ppm. In areas in which copper deficiency is a problem in goats, a mineral mixture with 0.5% copper sulfate should be offered on a free-choice basis. This level of copper, however, may be toxic for sheep.2 In extremely deficient areas, copper needles can be administered orally, or copper can be injected parenterally.



Copper Toxicity


Copper toxicity is a much larger problem in sheep than in goats. In sheep, the magnitude of difference between copper deficiency and copper toxicity is quite small. Copper toxicity can occur in sheep as a result of simple mixing errors during the formulation of mineral premixes, or from feeding mineral mixes formulated for species other than sheep, and can be exacerbated by the ingestion of toxic plants (e.g., lupines, alkaloid-containing species) and stress. Sources of toxic concentrations of copper include premixes, trace mineral supplements made for species other than sheep, copper sulfate–containing foot baths, feedstuffs containing high levels of copper (horse, hog, or chicken feeds), and some nontraditional feedstuffs (broiler litter). Signs of copper toxicity include increased respiration, depression, weakness, hemoglobinuria, and icterus, with sudden death in some instances. Gross histopathologic findings in affected animals include signs of a massive hemolytic crisis and dark, hemoglobin-filled kidneys. Treatment includes administration of d-penicillamine (26 mg/kg once a day for 6 days) and ammonium tetrathiomolybdate (1.7 mg/kg IV every other day for three treatments). The control of methemoglobinemia should be specifically addressed (see Chapter 12). Goats are closer to cattle than to sheep in susceptibility to copper toxicity.



Cobalt


Cobalt is used by rumen bacteria in the formation of vitamin B12. It is deficient in some highly organic or poorly drained soils. Cobalt deficiency in sheep or goats is characterized as a classic B12 deficiency, with signs and symptoms including lack of appetite, emaciation, anemia, and “wasting disease.” Cobalt deficiency is associated with white liver disease, although phosphorus and copper deficiencies and chronic parasitism also play roles in pathogenesis. Animals with this condition have excessive ophthalmic discharge, and their skin becomes extremely pale. Necropsy reveals a fatty liver (see Chapter 5).


To determine whether a cobalt deficiency exists, the clinician must evaluate the complete diet. Serum or urinary methylmalonic acid is increased and serum vitamin B12 and liver cobalt concentrations are depressed in cobalt deficiency. Diagnosis may be difficult, however, because of the normally low tissue concentration of cobalt. A diet with a cobalt concentration of 0.1 ppm is adequate in most instances, but dietary levels below 0.06 ppm should be considered deficient. If a frank deficiency exists, a cobalt-supplemented trace mineral mixture should be fed ad libitum. Cobalt toxicity is of minimal concern with most sheep and goat operations under typical conditions in North America.2



Iron


Iron deficiency in sheep and goats is quite rare under grazing conditions. Lambs or kids raised in total confinement and deprived of access to pasture and earth-floored stalls or paddocks may become deficient, however. Iron deficiency is exacerbated when young animals are fed a milk replacer deficient in iron. Newborn kids and lambs are born with minimal iron stores. Iron is an important component of hemoglobin, and a deficiency can result in microcytic-hypochromic anemia. Iron deficiency is a rare problem in adults, except in cases of excessive parasitism.


In kids and lambs with diagnosed iron deficiency, iron dextran (150 mg given intramuscularly) at 2- to 3-week intervals may prove a valuable therapy.9 Parenteral iron dextran may be toxic, and caution is indicated with its use.9 If selenium deficiency also exists, the use of iron dextran can result in painful muscle reactions. The dietary iron requirement generally is 30 to 40 ppm.



Iodine


Iodine deficiency is more common in certain geographic regions of North America, particularly the “Northern Tier” of the United States. Iodine availability is depressed by methylthiouracil, nitrates, perchlorates, soybean meal, and thiocyanates. Minerals that interfere with iodine absorption include rubidium, arsenic, fluorine, calcium, and potassium. Iodine appears to be most available for use by the body during winter months and during lactation. The form or “state” in which iodine exists in the feed alters availability—iodates are absorbed more readily than iodides. Signs of iodine deficiency include goiter, poor growth, depressed milk yield, pregnancy toxemia, and reproductive abnormalities including abortion, stillbirth, retained placentas, irregular estrus, infertility, depressed libido, and birth of small, weak, and either hairless or short- and fuzzy-haired newborns. Lambs or kids born to iodine-deficient dams may have enlarged thyroid glands. Affected kids can be treated with 3 to 6 drops of iodine (Lugol’s solution) daily for 7 days.


An enlarged thyroid in the kid commonly is a congenital problem unassociated with dietary iodine (see Chapter 9). After a thorough examination of the diet, if iodine deficiency is still suspected, the clinician can measure the serum or plasma thyroxine levels, which are lowered in deficient states, to assess the body status. Iodine is readily absorbed, so most sources will work well in salt-mineral mixtures or feed supplements. Iodine levels of 0.8 ppm for lactating animals and 0.2 ppm for nonlactating ewes or does usually are sufficient for normal function. Applying iodine (1 to 2 mL of tincture of iodine or Lugol’s solution) to the skin of a pregnant female once each week is a labor-intensive but rewarding method of preventing iodine deficiency–induced hypothyroidism. Hyperiodinism occasionally is associated with the feeding of kelp or related plants in mineral mixtures. This clinical problem may be encountered in the occasional pet or dairy goat. Simply removing the iodine source may be all that is required for treatment of toxicity.2



Zinc


Zinc deficiency–related disease or dysfunction has been reported in sheep and goats. Zinc availability is improved with the presence of vitamin C, lactose, and citrate in the diet. Oxalates, phytates, and large dietary concentrations of calcium, cadmium, iron, molybdenum, and orthophosphate all depress zinc availability. Zinc concentrations usually are higher in legumes than in grasses, but legumes invariably contain large concentrations of calcium, which can depress zinc availability. Zinc tends to be less available from cereal grain. Signs of zinc deficiency include dermatitis and parakeratosis, depressed milk production, impaired appetite, poor feed utilization, slowed growth, increased susceptibility to footrot, diminished hair growth on legs and head, swollen joints, poor growth, decreased reproductive performance, reduced testicular development, impaired vitamin A metabolism, and increased vitamin E requirements. Male goats appear to be more sensitive to the potential for adverse effects of marginal zinc intake.


When zinc deficiency is suspected, the clinician should carefully sample all constituents of the diet. Serum or plasma should be properly collected into tubes specifically designed for trace mineral analysis (royal blue top or trace mineral tubes). Hemolysis alters the accuracy of serum and plasma samples, because red blood cells have high zinc concentrations. Liver samples yield the most reproducible measurements of the zinc status of the animal. Both polystyrene containers and brown paper bags may be contaminated with zinc and should not be used for sample collection. Diets containing 20 to 50 ppm of zinc usually are sufficient, except for animals that consume a high percentage of legumes in their diets. In these instances, a chelated form of zinc is indicated. Providing trace mineral–salt mixes with 0.5% to 2% zinc usually prevents deficiency. The difference between required and toxic amounts is quite large, so zinc toxicity is rare under most conditions.2



Selenium


The absorption of selenium from the small intestine is enhanced by adequate dietary levels of vitamins E and A and histidine. Large dietary quantities of arsenic, calcium, vitamin C, copper, nitrates, sulfates, and unsaturated fats inhibit selenium absorption. Legumes usually are a better source of selenium than are grasses, which in turn are superior to cereal grains (see also Chapter 11).


The signs of selenium deficiency include nutritional muscular dystrophy, particularly of the skeletal and cardiac muscles of fast-growing young lambs or kids, and retained placentas. Other signs associated with insufficient selenium include poor growth, weakness or premature birth of lambs or kids, depressed immune function, mastitis, and metritis. Most often, selenium deficiency is observed in lambs between birth and 8 weeks of age.


Serum selenium concentrations are difficult to interpret because they may reflect dietary intake over the past 2 to 4 weeks. Whole blood selenium is reflective of dietary selenium intake over the past 100-plus days.


Liver biopsy is the the most accurate method for diagnosing selenium deficiency. Our own preference, however, is to use whole blood selenium to determine selenium adequacy. Diets containing 0.1 to 0.3 ppm of selenium usually are adequate. The upper limit (0.3 ppm) should be fed during the final trimester of pregnancy. Mineral-salt mixes should contain between 24 and 90 ppm selenium in deficient regions. Of course, dietary limits may be restricted to different levels in different countries and regions of the United States. In cases of frank deficiency, injectable vitamin E and selenium preparations may be given. Selenium toxicity may occur, but deficiency is the more prevalent problem. Toxicity is characterized by wool break, anorexia, depression, incoordination, and death.2



Vitamins


Because the rumen normally synthesizes B vitamins in healthy sheep and goats, the only vitamins needed in the diets of nonstressed animals are the fat-soluble vitamins: A, D, E, and K. If an animal has altered rumen function, is parasitized, is on a low-fiber diet, or is being given long-term antibiotic therapy, supplemental B vitamins may be of value.



Vitamin A


Vitamin A is involved in numerous bodily functions. It is essential for growth, proper skeletal development, normal reproduction, vision, and epithelial tissue integrity. Signs of vitamin A deficiency include weight loss, depressed immune function, night blindness, decreased fertility, and hair loss. Vitamin A can be stored in the liver for 4 to 6 months or longer. Green, vegetative forage meets the daily vitamin A requirement for sheep and goats, which is 105 international units (IU)/kg of body weight/day for nonlactating animals.2 During late gestation, the requirement increases to 150 IU/kg/day, and for lactation, 175 IU/kg/day. For conversion purposes, one retinol equivalent (RE) is equal to 3.33 IU. Plants are not a source of preformed vitamin A but instead contain vitamin A’s carotenoid precursors.2


Hay that is brown and dry and has been stored for long periods probably is deficient. Vitamin-mineral supplements that also contain oxidizing agents (e.g., copper, iron) are subject to oxidative destruction during storage. Although the label may indicate that vitamin A is present, its activity may be minimal.



Vitamin D


Vitamin D requirements generally are met if the animals are exposed to sunlight. In confinement feeding operations or during sustained overcast or cloudy conditions, vitamin D should be supplemented. Vitamin D deficiency can occur in heavily wooled lambs raised with limited access to sunlight or sun-cured forages. Winter months tend to be the most common time for marginal blood vitamin D concentrations.


Vitamin D, along with calcium and phosphorus, is important for normal bone integrity. Deficiencies can result in rickets (see Chapter 11). Plants, both fresh and in the form of hay (particularly sun-cured hay), contain abundant quantities of ergocalciferol (vitamins D2 and D3). The vitamin D requirement for sheep is 5 to 6 IU/kg of body weight/day, except for early-weaned lambs, which have a requirement of 6 to 7 IU/kg/day.2 For conversions, 1 IU of vitamin D equals 0.025 μg of crystalline D3.2



Vitamin E


Vitamin E is a biologic antioxidant that plays a major role in maintaining cell membrane integrity. It is closely associated with selenium in its mode of action, and a deficiency of either can lead to white muscle disease, depressed immune function, and depressed fertility in sheep and goats. Lambs from vitamin E–deficient ewes may exhibit stiffness, paralysis, and pneumonia. If a higher-than-expected incidence of infection and disease is noted in the herd or flock, the keeper or clinician should investigate adequacy of vitamin E intake. In selenium-deficient areas, young lambs generally should be given extra vitamin E and selenium by injection. Vitamin E is poorly stored in the body, so daily intake is crucial. Although vitamin E is found in most good-quality forages, if females are consuming poor-quality hay (particularly in selenium-deficient areas), supplementation is required. Feeds rich in vitamin E include alfalfa meal, cottonseed meal, and brewer’s grains. Some feedstuffs (e.g., corn, feeds containing high levels of sulfur, onions) decrease vitamin E availability. The 2007 National Research Council (NRC) recommendation for vitamin E requirements of small ruminants is 5.3 IU/kg of body weight/day. This recommendation is for all classes of sheep and goats.2



Vitamin K


If a ruminant animal is healthy, the keeper does not need to supplement vitamin K. Vitamin K is important for normal blood clotting and vision. In healthy animals it is produced in sufficient quantities in the rumen and lower gut.



Mineral Feeding


A salt block or loose salt is just that—a block or loose mixture of NaCl. Trace mineral salt in block or loose form is composed of NaCl (usually 98% to 99%) with added trace microminerals. The adequacy or content of certain minerals in the block or loose salt mixture generally is not specified. The nutritionist or clinician should carefully evaluate the type of salt-mineral supplement that is being offered to sheep or goats.


Most adult ewes consume around 0.3 to 0.8 kg of a mineral mix per month, or approximately 10 to 28 g daily. Sheep and goats maintained in dry lots usually consume more than this, whereas those that graze or browse on range consume less. Although commonly used, salt blocks are inappropriate for both sheep and goats, and their use can lead to inadequate mineral intake and the occasional broken tooth.


Complete mineral mixtures should be used for animals grazing poor-quality forages, and for breeding, pregnant, and lactating animals. A useful mixture of 40% dicalcium phosphate and 60% trace mineral salt offered ad libitum generally provides an effective yet inexpensive salt-mineral supplement. If vitamin E supplementation is required, 1 kg (2¼ lb) of a vitamin E supplement containing 44,100 IU/kg can be combined with 22.7 kg (50 lb) of trace mineral salt. If animals consume 10 to 17 g of the mixture daily, requirements for vitamin E should be met. In situations in which the amount consumed may not be adequate to meet these requirements, the keeper can monitor intake by weighing the mineral being offered weekly. If animals are not consuming enough of the supplement, the addition of corn, molasses, or soybean meal may enhance intake. If too much of the mixture is being consumed, the addition of white salt will curtail intake. Mineral supplementation should be based on individual farm practices, forage analysis, stage of production, and breed. As a general guide, mineral supplementation should be year round.



Feed Additives


To date, very few feed additives have been approved by the U.S. Food and Drug Administration (FDA) for use in sheep and goats. Two antibiotics, chlortetracycline and oxytetracycline, have been approved as feed additives for sheep in the United States. Dietary antibiotics may improve average daily gain, increase feed conversion, and reduce the losses associated with certain diseases (e.g., pneumonia, enterotoxemia) of lambs and kids when incorporated into creep feeds or finishing diets. Responses are variable and depend on management and the degree of stress the lambs are experiencing. Chlortetracycline and tetracycline are labeled in the United States for increased feed efficiency and improved body weight gain (20 to 60 g/ton of feed), for the prevention of Campylobacter fetus-associated abortion in breeding ewes (80 mg/animal/day), and for the treatment of bacterial pneumonia caused by Pasteurella multocida and enteritis caused by Escherichia coli (22 mg/kg of body weight/day). Both of these antibiotics have been successfully used (off label) in similar dosages in goats to treat the conditions listed for sheep. These antibiotics may be milled into complete diets or top-dressed onto feeds to treat footrot or conjunctivitis in situations in which individual animal treatment is difficult. Individual animal intake may vary, with resultant differences in response to therapy. Whenever feed-based antibiotics are used, anorexic animals will have insufficient intake for proper therapy.


Two ionophores, lasalocid and monensin, are approved by the FDA as feed additives for control of coccidiosis in sheep and goats, respectively. Both are approved for confinement feeding only, and neither is approved for use in animals whose milk is to be used for human consumption in the United States. Feeding these ionophores to ewes or does 30 days before they give birth can reduce the shedding of infective oocysts and may decrease pasture contamination and resultant coccidiosis infection in young lambs or kids. Both agents have value in improving weight gain and feed efficiency in adults and young growing animals. Ionophores also enhance propionic acid fermentation in the rumen, thereby increasing the pool of glucose precursors and aiding in the prevention of pregnancy toxemia in late-term ewes and does. These drugs have the added benefit of decreasing the incidence of free-gas bloat in animals on high grain–low forage diets (e.g., show lambs, feedlot lambs).


Decoquinate is another anticoccidial feed additive that is licensed for use in sheep and goats in the United States. However, it is not approved for use in animals producing milk for human consumption. Decoquinate acts early in the life cycle of coccidia, before they can cause gastrointestinal damage, therebye preventing some of the more serious consequences of infection. Decoquinate is very safe and can be added to feed, mineral mixtures, and milk or milk replacers. Lambs or kids at risk for the development of coccidiosis secondary to stress or environmental contamination and ewes or does in late gestation are likely candidates for the use of this feed additive. To maximize their effectiveness, decoquinate-containing feeds should be provided continually for a minimum of 28 days.


The dewormer morantel is approved as a feed additive for goats to control gastrointestinal nematodes. Feed additive anthelmintics are valuable for use in animals that are difficult to handle individually because of temperament or lack of facilities. However, if anthelmintics are fed continuously and consistent therapeutic intake is not met, anthelmintic resistance will occur.


The anionic salts ammonium chloride and ammonium sulfate both are urinary acidifying agents that help prevent certain types of urolithiasis when added to the diets of rams, bucks, and wethers. Urolithiasis may occur in males (in which the urethral diameter is smaller than in females) consuming high-grain diets. This is particularly true in pet goats, breeding bucks or rams, and feedlot lambs. These anionic salts tend to be unpalatable, however, and in effective doses (200 mg/kg/day), their use may result in depressed feed intake.


The term yeast culture refers to yeast and the medium on which it is grown. This product can be dried, preserved, and used as a feed additive. Although the mode of action has not yet been determined, the feeding of some yeast cultures may stimulate dry matter intake and fiber digestion, especially in mildly stressed animals. These yeast cultures may stimulate the growth of ruminal bacteria, which utilize lactic acid. The quality of these preparations should be examined closely before their use. Yeast culture may be useful in easing animals into grain-rich diets and minimizing rumen upset during the diet transition phase.


Buffers are salts that resist pH changes, whereas neutralizing agents neutralize acid and therefore increase pH. Some feed-grade buffers include sodium bicarbonate, sodium sesquicarbonate, sodium bentonite, and calcium carbonate. Magnesium oxide, sodium carbonate, and sodium hydroxide are neutralizing agents. Buffers and neutralizing agents can be added to high-grain diets (e.g., diets fed to feedlot lambs, show lambs, and dairy animals) to help limit the rapid changes in ruminal pH associated with the ingestion of excessive concentrates. Sodium bicarbonate probably is the most widely used of these chemicals. The response to feeding buffers appears to be variable, except when they are used in dairy animals receiving high-grain diets. Buffers are of less value when forage-based diets are fed. In dairy goats and sheep, buffering agents improve milk production, minimize milk fat depression, decrease the incidence of lactic acidosis–rumenitis complex, and improve overall health. These buffers may be fed ad libitum to dairy goats, included in a total mixed diet at around 1%, or top-dressed onto the feed.



Fiber


Fiber is an important component of the diet of a ruminant animal. Without adequate fiber in the diet, normal rumination does not occur. In sheep, feeding a concentrate-based diet with limited amounts of fiber results in “wool pulling” as the animals seek a roughage source. To promote a healthy rumen, the dietary fiber content generally should be greater than 50%.


Fiber also is required in the diet to maintain acceptable levels of milk fat. The particle size of the fiber is important. It is generally accepted that a minimum particle size of 1 to 2.5 cm is appropriate to stimulate normal rumination, although the effect of smaller particles is not well documented in sheep and goats. Pelleted roughage does not meet the requirement for fiber size. Animals being fed pelleted forage or lush pasture should be offered hay.13



Pelleted Feeds


The process of pelleting compacts feeds by forcing them through a die. Pelleting of feeds decreases waste, allows for easier storage and mechanization, and decreases labor. However, it usually increases the total feeding cost. Compacting the feed ingredients reduces or eliminates fines and dust particles, thereby increasing palatability. The pelleting process reduces separation and feed sorting by the animal, preventing the intake of only certain parts of the total feed. Because pelleting usually entails grinding, particle size usually is reduced, somewhat improving digestibility. However, feeding pellets can result in decreased milk fat in dairy animals, an increased incidence of ulcers and choke, and urolithiasis in males. Pelleted rations may increase the incidence of phosphatic calculi, owing to decreases in saliva production, thus lowering phosphate excretion by the gastrointestinal tract. Pelleted rations can therefore increase urinary excretion of phosphorus. Pelleted rations also are associated with increased mucoprotein excretion in the urine. Pelleting also may reduce the content of vitamins A, E, and K, or destroy these nutrients outright, in the feed. In formulating pelleted feeds, manufacturers should fortify these nutrients in the pellet. The animal keeper or producer should weigh the costs versus benefits of pelleted feedstuffs.



Feed Analysis


Both sheep and goats can derive nutritional value from numerous feeds. A listing of a wide array of feeds and their nutritional content can be found in the 2007 NRC recommendations for small ruminants.2 For simplicity, energy values are reported as TDN. Many feeds have limitations on their use because of such factors as fat content, palatability, moisture content, antinutritional factors, and other attributes beyond the scope of this discussion.


To analyze the nutrient content of a given feedstuff, the clinician must obtain a representative sample. For hay analysis, random sampling of approximately 10% of the bales is adequate. With large round bales, a core sample into the round surface of the bale to a depth of approximately 78 cm is ideal. Most sampling devices provide an approximate 2.5-cm-diameter core from the bale. All of the core samples should be combined into one container and thoroughly mixed. From this combined mix, the clinician should properly package a subsample of approximately 0.22 kg and send it to a laboratory for analysis. Samples of silage and other high-moisture feeds should be frozen before shipment to the testing laboratory. To analyze bulk feeds that are stored in bins or other storage facilities, the clinician should take several random grab samples as the feed is being augered or unloaded.


Forage can be evaluated by appearance, albeit with much less accuracy than with some sort of laboratory analysis. Green, leafy forage that is free of mold or weeds usually is more nutritious. Goats tend to select leaves when fed hay; thus hay analysis may not always apply to nutritional intake.


After a representative sample arrives at the laboratory, it is analyzed for a variety of nutritive components. First, the sample is assayed for moisture content. Most feeds contain approximately 10% to 15% moisture, or possibly less in arid environments. The dry matter of a feed is therefore important, and for comparison the nutrient content of the feed is reported as percent dry matter. If the moisture content exceeds 15%, mold contamination is typically a problem. In addition, total ash content also may be determined and amounts of individual minerals measured. Total ash content may be of value for analysis of various byproduct feeds in which dust or soil contamination may be a problem.


The fiber content also should be determined. Most laboratories use the Van Soest procedure, which is based on the use of detergents. The first step is to boil the sample in a neutral detergent solution and separate the cell contents from the fiber. The undissolved fraction is referred to as the neutral detergent fiber (NDF). This NDF fraction is then boiled in an acid detergent solution to dissolve the hemicellulose, which leaves behind the acid detergent fiber (ADF). This fraction is dissolved in 72% sulfuric acid, which solubilizes the cellulose. The remaining lignin and silica are separated by ashing the sample. The NDF is an estimate of the amount of hemicellulose, cellulose, and lignin the sample contains, whereas the ADF estimates the amount of only cellulose and lignin. As the NDF content of a feedstuff rises, the bulkiness of the feed also increases—that is, NDF is negatively correlated with dry matter intake. As the ADF content of a feed rises, its digestibility is decreased. Pelleting or grinding usually results in a greater dry matter intake, even for feedstuffs with relatively high NDF content. Based on the determined levels of the various fiber fractions, prediction equations are used to compute TDN content and various other values for energy content (e.g., metabolizable energy, net energy).


The last major nutrient that is measured is crude protein. The sample is analyzed for nitrogen content, and then crude protein is calculated as percent nitrogen multiplied by 6.25. The crude protein value cannot indicate if any or how much of the protein has been damaged by heat. Heat damage often results in decreased digestibility. This method of protein analysis does not differentiate between NPN and natural protein. Protein content reported as digestible protein is formulated from crude protein content. Unfortunately, digestible protein is of limited practical value in developing rations. Additionally, samples may sometimes be analyzed for fat. Table 2-1 illustrates sample hay analyses.


TABLE 2-1 A Sample Analysis for Fescue Hay




































Constituent Content Determined on Dry-Matter Basis
Moisture 12.75%
Dry matter 87.25%
Crude protein 12.31%
Fiber  
NDF 62.00%
ADF 39.00%
Total digestible nutrients* 58.09%
Net energy—lactation* 1.31 mcal/kg
Net energy—maintenance* 1.25 mcal/kg
Net energy—grain* 0.58 mcal/kg

ADF, Acid detergent fiber; NDF, neutral detergent fiber.


* Calculated from prediction equations.


Different testing laboratories use different equations to predict energy values. One such equation in common use is as follows:



image



The equation balances using either the ADF (39%) or the TDN (58.09%) values from the analysis provided in Table 2-1. In contrast with this simple equation, the various net energy prediction equations use cubic and quadratic terms, which are much more complex. The NDF fraction can be used to estimate the animal’s voluntary dry matter intake:



image



Again, using the information from Table 2-1, the equation is solved as follows:



image



Thus animals provided with the hay in Table 2-1 would consume approximately 1.9% of their body weight in dry matter.


Another nutritional measure that may be reported on a forage analysis is relative feed value (RFV), which is calculated as follows:



image



where digestible dry matter (%) = 88.9 – (0.779×ADF [%]) For this example, therefore, the equation is completed as follows:



image



RFVs can exceed 100 and often do so for good-quality alfalfa. However, this measure does not take into account the crude protein content of the forage, which must be evaluated separately. The poorer the quality of a forage, the longer it requires for digestion. Poor-quality forage remains in the rumen for a longer period, thereby indirectly limiting feed intake. Keepers purchasing feeds would do well to make decisions based on RFV. During diet formulation, however, TDN and protein concentrations most often are used as guidelines.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Feeding and Nutrition

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