Printer Friendly

Chapter 20 Feeding sheep.

The mountain sheep are sweeter, But the valley sheep are fatter; We therefore deem it meter To carry off the latter.

THOMAS LOVE PEACOCK, 1785-1866

The nutritional phases in the sheep production cycle, illustrated in Figure 20-1, include:

Ewe: Lactation, flushing/breeding, early-mid gestation, late gestation

Lamb: Liquid feeding/creep feed, growing/finishing

A sample growth rate is plotted in Figure 20-2.

THE EWE AND EWE LAMB

Lactation

Ewes achieve their peak milk production within 2 to 4 weeks after lambing, and 70 percent of their total milk production will be made in the first 8 weeks. After 8 weeks, lactation will have minimal impact on nutrient requirements of the ewe. Ewes nursing twins will make 20 to 50 percent more milk than ewes nursing singles. Information about when the milk is produced and how much milk is produced should be applied to ewe nutritional management. To the extent possible, ewes in similar production status should be grouped together so that they can be fed diets targeted to meet their nutritional needs. The primary nutrient requirement that will vary among lactating ewes will be the need for energy. Ewes will lose body weight if the energy demand for milk production is greater than energy intake. Ewes should be managed to lose no more than one body condition score (BCS) during the first month and should gain this back during the second month of lactation (Snowder & Glimp, 1991).

Lambs can be weaned as early as 4 weeks if they are eating creep feed at a rate of 0.5 lb. daily. It is more common to wean lambs at 6 to 10 weeks. Absent the suckling lamb(s), the mammary glands cease to produce milk and the nutrient requirements of the ewe are reduced. If ewes have not yet regained the weight lost during the late gestation and lactation phases, they should be fed a diet to support gain after weaning.

[FIGURE 20-1 OMITTED]

[FIGURE 20-2 OMITTED]

Ewe Lambs

Ewe lambs are young ewes that are be bred to lamb at 12 to 14 months of age. These animals are selected from the market sheep at 3 to 4 months of age (80 to 90 lb.) and are usually managed as a separate flock. Success with ewe lambs requires a high level of nutritional management. Their diet should support growth such that they reach 65 percent of their mature body weight by breeding time at 7 to 9 months, but they should not be allowed to get fat. Lactation is a critical period for ewe lambs because these animals are still growing and will not have the stored reserves of nutrients that mature ewes have. Ewe lambs are generally not bred when sheep are managed under range conditions because of the difficulty in managing nutrient intake on the range.

Flushing/Breeding

Flushing is the practice of increasing the nutrient intake (primarily energy but also protein) around the time of breeding to improve ovulation rate and, hence, the lambing rate. Lambing rate would be 100 percent if each ewe in the flock gives birth to a single lamb; it would be 200 percent if each ewe has twins. Flushing has been shown to result in a 10 to 20 percent improvement in lambing rate (Cole & Cupps, 1997) in ewes of moderate body condition (Gunn, 1983). Where it is effective, the increased nutrient intake from flushing has an impact on the developing follicles of the ovary.
Figure 20-3

Sheep body condition scoring (Thompson & Meyer)

Condition 1 (Emaciated)

Spinous processes are sharp and prominent. Loin eye muscle is
shallow with no fat cover. Transverse processes are sharp; one can
pass fingers under ends. It is possible to feel between each
process.

Condition 2 (Thin)

Spinous processes are sharp and prominent. Loin eye muscle has
little fat cover but is full. Transverse processes are smooth and
slightly rounded. It is possible to pass fingers under the ends of
the transverse processes with a little pressure.

Condition 3 (Average)

Spinous processes are smooth and rounded and one can feel
individual processes only with pressure. Transverse processes are
smooth and well covered, and firm pressure is needed to feel over
the ends. Loin eye muscle is full with some fat cover.

Condition 4 (Fat)

Spinous processes can be detected only with pressure as a hard
line. Transverse processes cannot be felt. Loin eye muscle is full
with a thick fat cover.

Condition 5 (Obese)

Spinous processes cannot be detected. There is a depression between
fat where spine would normally be felt. Transverse processes cannot
be detected. Loin eye muscle is very full with a very thick fat
cover.


Flushing is accomplished by moving ewes onto a high-quality pasture or by feeding grain, usually at a rate of 0.25 to 0.5 lb. The period of flushing usually starts 2 weeks before breeding and may continue for several weeks into the breeding season. The reason for continuing flushing into the breeding season is to decrease embryonic death loss. Flushing is effective in improving reproductive performance in ewes that are to be bred either early or late in the breeding season when ovulation rates are less than optimal. Because flushing is of short duration, it will usually not have a significant impact on the ewe's body condition.

Body Condition Scoring

Body condition scoring in sheep is generally based on a 5-point scale similar to the dairy system (Figure 20-3). The 9-point system used in the beef industry is also sometimes used for sheep (Figure 17-9). Moderate body condition corresponds to a body condition score (BCS) within the range of 2.0 to 3.5 on a 5-point scale. Outside this range of body condition, flushing appears to have less of an impact on ovulation rate than does the body condition.

Early/Mid-Gestation

The gestation length of a ewe is approximately 5 months (146 to 150 days). The embryo becomes attached to the uterine wall at about 45 days postbreeding, the development of the placenta is completed by 90 days, and up until about 100 days into the pregnancy, the embryo increases only slightly in size. Severe nutrient deficiencies can affect embryonic development, but nutrients during this time will be used primarily for maintenance functions, fleece production, and, if the pregnant animal is a ewe lamb, growth. Due to the relatively low nutrient demands of early/mid-gestation, this is a period in which ewes can be fed to achieve the targeted BCS at lambing. As with dairy cows, the target score at parturition is 3.5.

Late Gestation

Two thirds of the fetal growth occurs during the last third of gestation, and the nutrition of the ewe during this period will have a significant impact on the survivability of her lamb(s). Lambs born to ewes that were fed poorly during this period will have reduced energy reserves as evidenced by low birth weights, and in the case of multiple births, dissimilar birth weights. Such ewes will also give birth to lambs with a reduced number of functional wool follicles. This may have an impact on lamb survivability, particularly if the lamb is born in a cold environment. The ewe that is fed poorly during the last part of gestation will have a decreased milk production potential because this is the time when mammogenesis occurs. Even if the ewe is well fed once lactation begins, if mammogenesis has not progressed properly, there will be less milk for the lamb(s).

The nutrient requirements for the last 6 weeks of gestation will be considerably greater for the ewe carrying twins than for the ewe carrying a single fetus. If ewes do not receive adequate energy from the feed they are eating during this period, they will mobilize body fat to meet their energy needs. An excessive reliance on body fat to meet energy needs results in a problem called pregnancy toxemia in sheep and goats. As body fat is mobilized, ketone bodies accumulate in the blood. Pregnancy toxemia is also called ketosis. Aewe with ketosis lags behind the flock, shows labored breathing, staggers, and finally becomes paralyzed. Ketosis is described in Chapter 18. For sheep, goats, and dairy cattle, ketosis is the result of an energy deficit. In cows, ketosis is more likely to occur during early lactation, but in ewes and does, ketosis is more likely to occur during late gestation, especially if the ewe or doe is carrying twins or triplets.

Accelerated Lambing

In accelerated lambing programs, animals are managed to produce more than one lambing per year. In these programs, it is possible to have three lamb crops per ewe in 2 years or five lamb crops per ewe in 3 years. The decision to use an accelerated lambing program will have a significant impact on the choice of sheep breed, marketing options, and labor inputs, as well as on nutritional management. Ewes must be fed to return to breeding weight (BCS of 3.5) sooner than if they were to lamb only once per year. Early weaning of lambs may be useful in accelerated lambing programs.

THE LAMB

Colostrum

The structure of the ewe's placenta is described as epitheliolchorial. This type of placenta does not allow antibody immunoglobulins to pass from the ewe into the blood of the fetal lamb(s). The ewe's first milk or colostrum is rich in these antibody immunoglobulins and the newborn ruminant receives passive immunity by intestinal absorption of the antibodies present in colostrum. Antibodies are made of protein and protein is normally digested in the intestine into its component amino acids. Fortunately, this does not happen in the newborn ruminant. If it did, the antibodies would be destroyed. For a short time after birth, the neonatal ruminant is able to absorb the antibodies in colostrum intact. However, this ability begins to decline within minutes of birth. Colostrum is also a laxative and contains higher levels of some nutrients than does regular ewe milk. To ensure prompt and adequate colostrum intake, neonatal ruminants are often bottle-fed colostrum.

The recommendations for colostrum consumption for all ruminants are (1) neonates should receive an amount of colostrum that is equivalent to 10 percent of the birth weight or 1.5 ounces per pound of body weight within 12 hours of birth; and (2) half this amount should be ingested within 2 hours of birth, the sooner the better. A 10-lb. lamb should, therefore, receive about 1 lb. of colostrum. One pound of colostrum occupies a volume of approximately 0.5 quarts or 15 ounces.

If the ewe is unable to provide her lamb with colostrum, colostrum may be provided from another ewe or from frozen ewe or cow colostrum, warmed to body temperature and bottle-fed.

Creep Feed

Creep feed is feed that is placed in a location that makes it accessible to the lambs but inaccessible to the ewes. The location should be warm, well lit, and not far from where the ewes rest. Creep feed for lambs may contain antibiotics to improve gain and feed efficiency, and also to provide some protection against low-level infection. The issues that must be considered in deciding whether or not to creep feed lambs are the same as those for beef animals (Chapter 16). In addition, creep feeding lambs will reduce the stress on ewes with twins and triplets; this may be especially important with accelerated lambing programs.

Early Weaning

At birth, the lamb's rumen is nonfunctional. Until the rumen becomes functional, needed nutrients must be supplied through milk or milk replacer. Early weaning necessitates the use of milk replacer.

Traditionally, lambs stay with the ewe for about 6 to 10 weeks, though weaning can be successful as early as 4 weeks if lambs are eating creep feed at a rate of 0.5 lb. daily. Early weaning involves removing lambs from ewes shortly after they have received colostrum and feeding them milk replacer until weaning. Early weaning involves more labor and feed expense than leaving lambs with ewes, but it offers the following advantages:

* Increased weight gains

* Lambs are ready for market at a younger age

* Pasture-sparing effect-more ewes can be supported on a given pasture

* Less stress on ewes, which may help them to return to breeding condition more quickly (as would be necessary in accelerated lambing management)

* Fewer problems with parasitism and predators

When lambs are becoming accustomed to milk replacer, it should be fed warm. However, it is recommended that eventually milk replacer be self-fed from multiple nipple pails at a cold temperature. Cold milk replacer is consumed in smaller but more frequent meals than warm milk replacer, and is thereby utilized more efficiently.

Lambs can be weaned from milk replacer as small as 25 lb. and as young as 4 weeks of age. To be ready for weaning at this age, lambs should be well accustomed to creep feed, eating about 0.5 lb. daily. For this to happen, the creep feed should be made available to lambs at 1 week of age. Although week-old lambs will not eat significant amounts of creep feed, the small amounts ingested are important to establish a functioning rumen at an early age.

Growing and Finishing

Weaned lambs may be sent directly to a feedlot for finishing, or they may be placed on pasture or crop aftermath as part of a growing phase prior to finishing.

To be ready for most markets, lambs should have attained a degree of finish corresponding to a backfat depth of 0.1-0.2 in. Under some systems of management, lambs may reach this goal while still with the ewe, but most lambs in the United States will need to be placed on a finishing diet to reach this target. Larger-frame sheep will attain this level of finish at higher body weights than smaller frame sheep. Continuing to feed lambs that have attained 0.2 in. of backfat results in reduced profitability because these lambs are converting increasing amounts of feed energy into fat and this conversion is relatively inefficient.

At the feedlot, lambs should be given immediate access to free-choice water. The finishing diet will be a high-concentrate, energy-dense ration. Such rations may contain as much as 80 percent grain. Care should be taken to ensure that the lambs arriving at the feedlot are transitioned properly to the finishing diet. All changes of diet must be gradual to allow for proper adaptation of the ruminal microbes and the lamb. A gradual transition to the finishing diet will help prevent problems such as acidosis, enterotoxemia, and diarrhea. In warm weather, dry matter intakes (DMI) may improve if lambs are sheared soon after arrival at the feedlot.

Feeder space for self-fed lambs should be 3 to 4 in. per lamb; feeder space for limit fed lambs should be 9 to 12 in. per lamb (Table 12-5). Limit fed lambs should be fed at least twice daily.

It is important to know the growth potential of the lambs. Feeding a diet that would result in maximal gains in lambs with rapid growth potential to lambs with only moderate growth potential will increase fat deposition and reduce profitability. Ram lambs have higher feed intakes and higher nutrient requirements than do ewe lambs, and should be fed accordingly for maximum profitability.

SHEEP FEEDING AND NUTRITION ISSUES

Nutrition and Wool Production

Energy is the primary nutrient impacting wool production. However, energy-deficient sheep will be growing fewer high-protein microbes in the rumen. It may be this decreased ruminal protein production that most directly affects wool production. Except in the case of severe nutritional deficiencies, the impact of nutrition on wool production is quantitative; that is, mild deficiencies will result in reduced wool yield but will have no impact on wool quality.

Nutritional deficiencies will have different impacts on wool production depending on when they occur. If the gestating ewe is fed a deficient diet, her fetus will not fully develop all its potential wool follicles. If the neonatal lamb is fed a deficient diet, not all of its developed wool follicles will be capable of producing a wool fiber. This damage to the wool follicle will be permanent. If a mature sheep is fed a deficient diet, it may result in a temporary disruption of the normal wool follicle growth cycle.

Blocks for Pastured/Range Sheep

Under pasture and especially range conditions, there is limited opportunity to alter the nutrient intake of sheep. However, under some conditions, blocks that contain limiting nutrients can be provided to these animals. The nutrients most likely to be limiting for pasture- and range-fed sheep are salt, energy, crude protein, phosphorus, and vitamin A.

If energy is limiting, supplemental crude protein should be true protein from a source such as soybean meal rather nonprotein nitrogen (NPN) such as urea. This is because NPN can only be utilized if ruminal microbes have access to adequate energy in the form of fermentable carbohydrates. Salt supplements may be provided in block or in loose (granular) form. Loose salt is usually preferable because sheep may bite the blocks and damage teeth.

By changing block location, these feed supplements can be used to help manage pasture utilization.

Copper

The copper level of the total diet for sheep should be less than 25 mg/kg or ppm (National Research Council, 1980). This is because sheep accumulate copper in the liver more readily than do most animals. Eventually the copper destroys liver cells and is released into the blood, causing symptoms of anorexia, excessive thirst, and depression. Death usually follows within a few days.

The sheep's sensitivity to copper makes many products designed for species other than sheep unsuitable for sheep. Because molybdenum forms an insoluble complex with copper and thereby reduces its availability (Figure 9-1), it is possible to limit copper absorption through molybdenum supplementation. However, the Food and Drug Administration does not recognize molybdenum as a feed additive so the use of molybdenum to prevent copper toxicity in sheep will be a veterinary rather than a nutritional application. It should be emphasized that sheep do have a copper requirement and excess molybdenum may result in copper deficiency.

The Need for Vitamin D

Sheep on pasture normally will not require supplemental vitamin D because unless they have heavy fleeces, sheep are able to manufacture vitamin D from sterol compounds in their skin tissue when exposed to sunlight.

Bloat

Bloat is a concern with pastured ruminants, particularly with pastures heavy in legumes. In bloat, the gases of fermentation are trapped and cannot be eructated. Unless the resulting pressure is relieved, the animal will die. Feeding hay before or with pasture can help prevent bloat. The subject of bloat is discussed further in Chapter 16.

Processing Grains

The processing of grains, either into a mash/meal form or into a pellet, adds expense to the ration. The expense is usually warranted if it results in increased nutrient availability over feeding the unprocessed grains. With mature sheep, this is usually not the case. Mature sheep with good teeth chew their grain thoroughly so that there is usually no benefit from feed processing. For lambs, however, this may not be the case. There may be enough improvement in feed intake and nutrient availability to make grain processing a good investment when feeding lambs. In addition, grinding grain may be necessary if excessive sorting (preferential consumption) of feed ingredients becomes a problem.

Urinary Calculi

Urinary calculi are mineral crystals that form in the urinary tract from excess dietary minerals, primarily cations. The crystals grow and can block passageways in the urinary tract. Since the source of the calculi is excess dietary mineral, a logical prevention program would be to limit excesses of minerals, which also makes nutritional, economic, and environmental sense. Reducing the dietary cation-anion difference (DCAD) through the addition of anionic salts such as ammonium chloride or ammonium sulfate is also helpful in reducing the incidence of urinary calculi. For this reason, it is common in the feed industry to formulate sheep grain that includes ammonium sulfate or ammonium chloride at a level of 0.5 percent. Animals fed excess anions excrete acids in the urine and an acidified urine discourages the formation of urinary calculi. The companion application to this text calculates the DCAD in sheep rations.

Feeder Space

When providing supplemental feed to ewes, pelleted feed or whole grains should be spread out in such a way that all animals can feed at feeding time. This is important because ewes are generally limit fed and all will be eating at the same time. When using troughs or communal feeders, it is important that adequate feeder space be provided to ewes. Table 12-5 gives feeder space recommendations for livestock.

Prussic Acid Poisoning

Under certain conditions, some grasses--particularly forage sorghums--may accumulate hydrocyanic acid in their tissues. These conditions include stresses such as frost, severe drought, or a period of heavy trampling or physical damage. The breakdown of cell structure in these stressed plants results in a mixing of plant enzymes with cyanogenic glycosides in the plant, producing hydrocyanic acid. Hydrocyanic acid is a source of cyanide and is also known as prussic acid. Consumption of such crops by sheep or any grazing animal results in a disorder called prussic acid poisoning. Symptoms of prussic acid poisoning include convulsions, frothing at the mouth, breathing difficulty, and sudden death. The ensiling process removes the hydrocyanic acid and so these grasses can be safely fed as silage.

Nitrate Poisoning

Nitrate poisoning is described in Chapter 16. Sheep are especially prone to consuming nitrate-containing compounds such as commercial fertilizers. The pioneer cattlemen are said to have used this characteristic of sheep to drive sheep-raisers and their flocks from an area of free range in the public domain of the western United States. "Salting the range" refers to the practice of spreading saltpeter (potassium nitrate) in places where sheep would eat it and succumb to nitrate poisoning.

Poisonous Plants

Sheep will generally avoid plants that contain potential toxins. However, during times of feed shortage, toxic plants may be ingested. Tables 3-3, 3-4, and 3-5 list plant species that are toxic to sheep, grouped according to the nature of the toxicity.

Ruminal Acidosis

In ruminant animals, the term acidosis is generally applied to the condition in which the rumen contents drop in pH to below 6.2. There are two forms of ruminal acidosis: acute and subacute. The difference between acute and subacute ruminal acidosis relates to the rate and quantity of acid production and how long the acid condition persists in the rumen. For purposes of discussion here, subacute ruminal acidosis will be considered to exist when ruminal pH lies within the range of 5.7 to 6.2, and acute ruminal acidosis exists when ruminal pH falls below 5.7.

In acute ruminal acidosis, the ruminal pH drops rapidly to below 5.7. Acute ruminal acidosis may occur in feedlots when the transition to a concentrate-rich diet is poorly managed. Acute ruminal acidosis may result in death of the animal. Animals that survive acute ruminal acidosis may have sustained permanent damage to the rumen wall. These animals become chronic poor-performers due to an impaired ability to properly absorb nutrients.

Subacute ruminal acidosis is a more widespread problem than is the acute form. The ruminal pH characteristic of the subacute form of ruminal acidosis is 5.7 to 6.2. Subacute ruminal acidosis may occur in feedlots but it is also common in dairy animals fed for high rates of production.

The acid in ruminal acidosis originates during the ruminal fermentation of readily fermentable carbohydrates, primarily grain. The rate of fermentation of the carbohydrate in cereal grains varies, so some grains are more likely to be associated with acidosis than others. Wheat grain is the most rapidly fermented, followed by barley grain and then corn grain. Some processing methods such as steam flaking will increase the rate of fermentation of a cereal grain. The primary acid associated with grain fermentation is propionic acid. Acids are also produced from fermentation of carbohydrate in the forage component of the diet, but more slowly than from the grain portion. The primary acid associated with forage fermentation is acetic acid. Ruminal fermentation activities also produce lesser amounts of butyric and other organic acids.

The microbes that ferment the major carbohydrate in grains are the amylolytic bacteria, and those that ferment the major carbohydrate in forages are the cellulolytic bacteria. The primary product of the amylolytic bacteria is propionic acid. The primary product of the cellulolytic bacteria is acetic acid.

The cellulolytic bacteria are more sensitive to a reduction in ruminal pH than are the amylolytic bacteria. As a result, during acidosis, the proportion of acetate falls as the production of propionate rises. Figure 20-4 displays these relationships. Acidosis, therefore, leads to a decreased acetate-to-propionate molar ratio in the rumen. Because acetate is used to build milk fat, one theory as to the cause of milk-fat depression in ruminants suggests that acidosis results in an acetate deficiency. The more widely accepted theory faults the increased production of trans fatty acids in the acidic rumen. Milk-fat depression is discussed in Chapter 18.

Acetic and propionic acids produced by the ruminal bacteria are absorbed through the rumen wall into the portal blood that carries absorbed material to the liver. These acids are an important source of energy for the ruminant. The butyric acid made in the rumen is utilized as an energy source by the epithelial cells lining the rumen. Butyric acid that is not utilized by the rumen's epithelial cells is converted to ketones before absorption.

If too much grain is fed without appropriate forage or if there is an insufficient adaptation period when transitioning to a high-grain diet, the bacterial populations and the fermentation processes will be altered (Figure 20-5). Under these conditions, the population of lactic acid-producing bacteria in the rumen increases and there is a concomitant reduction in the use of lactic acid by other bacteria in the rumen. Lactic acid is a stronger acid than the acids discussed thus far: the pKa value is 3.85 for lactic acid compared to 4.76 for acetic acid, 4.87 for propionic acid, and 4.85 for butyric acid. These pKa values mean that in terms of its ability to reduce ruminal pH, lactic acid is about 10 times as strong as the volatile fatty acids normally produced in the rumen.

[FIGURE 20-4 OMITTED]

[FIGURE 20-5 OMITTED]

Animals with a ruminal pH of between 6.2 and 5.7 show variable DMI. In the rumen itself, there is reduced microbial growth and fiber fermentation. At a ruminal pH of less than 6.0, the ability of bacteria to derive energy from forages declines (Schwartzkopf-Genswein, Beauchemin, Gibb, Crews, Hickman, Streeter, & McAllister, 2003). DMI may be dramatically reduced if ruminal pH drops to less than 5.7. In the companion application to this text, ruminal pH is predicted from the level of physically effective NDF in the ruminant ration (Figure 18-4).

A reduction of ruminal pH leads to several conditions that contribute to the systemic problems associated with acidosis.

1. There is a change in microbial activity, leading to increased production of trans fatty acids.

2. There is a change in the population of microorganisms inhabiting the rumen, increasing the number of those that decarboxylate the amino acid histidine to create histamine.

3. Ruminal histamine concentration increases.

4. The rumen wall becomes inflamed, and histamine--along with bacteria--passes into the portal blood (Garner, Hay, Guard, & Russell, 2003)

The increased production and absorption of trans fatty acids leads to milk fat depression (Chapter 18).

The bacteria that are absorbed into the portal blood of an animal with ruminal acidosis cause liver abscesses. Liver abscesses result in significant economic losses from liver condemnation, reduced animal performance, and reduced carcass yield (Nagaraja & Chengappa, 1998).

An increase in the level of histamine in the blood causes changes in the pattern of blood circulation, especially in the hoof. Histamine is a powerful inflammatory agent. As such, it increases the permeability of blood vessels, allowing fluids to escape from the vessels and seep out into extracellular space. This seepage results in inflammation and blood stagnation. As a result of this stagnation, oxygen is not delivered in adequate amounts to the differentiating epithelial cells that are destined to become hoof wall. This cell damage in the hoof is evidenced as laminitis.

Ruminal acidosis combined with excess sulfur intake may lead to a disorder called polioencephalomalacia, which is discussed in Chapter 9.

Ruminal acidosis has been reviewed (Schwartzkopf-Genswein, Beauchemin, Gibb, Crews, Hickman, Streeter, & McAllister, 2003; Owens, Secrist, Hill, & Gill, 1998).

Enterotoxemia

Enterotoxemia, or overeating disease, is a common problem in finishing lambs, and also occurs in cattle, goats, horses, and rabbits. It occurs in stressed animals and/or animals whose diet has been changed without a proper transition. Enterotoxemia occurs when bacteria from the genera Clostridium and/or Escherichia proliferate in the intestine, producing toxins that are absorbed. Prevention involves ensuring that lambs have 7 to 10 days to make the transition from a high-forage diet to one containing large amounts of concentrate. Protection through vaccination is also possible, and in flocks where enterotoxemia is a constant threat, vaccinations should be routine practice. Symptoms include depression, grinding of the teeth, and death.

Grass Tetany

Grass tetany may occur in sheep turned out to lush pastures without being provided with a mineral supplement containing adequate magnesium. Grass tetany is described in Chapters 9 and 16.

White Muscle Disease

White muscle disease or stiff lamb disease is caused by a deficiency of selenium and/or vitamin E. Affected lambs are usually 3 to 8 weeks of age. The primary symptom is stiffness in the legs and death. Anecropsy reveals a paleness in the heart and skeletal muscle. Prevention involves ensuring that rations meet requirements for selenium and vitamin E. These nutrients may also be provided through injection.

Milk Fever or Parturient Paresis

The lactating ewe may be afflicted with parturient paresis or milk fever. Milk fever is described in Chapter 18.

Tall Fescue Toxicosis

Sheep that consume pasture or hay containing tall fescue that has been infected with an endophyte are susceptible to tall fescue toxicosis, which has various effects on health, production, and reproduction. Tall fescue toxicosis is discussed in Chapter 24.

Polioencephalomalacia

Polioencephalomalacia (PEM) is a disorder occurring most commonly in sheep and cattle that is caused by a thiamin deficiency. It may be caused by ingestion of feedstuffs containing thiaminases, the creation of a rumen environment encouraging the growth of thiaminase-producing bacteria, or excess sulfur intake. Symptoms of PEM include lethargy, blindness, gastrointestinal stasis, muscle tremors, convulsions, and death. PEM is discussed in Chapter 16.

END-OF-CHAPTER QUESTIONS

1. In the sheep industry, when is the threat of ketosis the greatest? What is a synonym of ketosis in the sheep industry?

2. Explain why mineral mixes formulated for other livestock are unsuitable for sheep.

3. Why is it usually unnecessary to feed supplemental vitamin D to pastured sheep?

4. Adjustment of the DCAD in sheep diets is helpful in preventing what disorder?

5. Explain how the fact that amylolytic bacteria are less sensitive to an acid environment than cellulolytic bacteria contributes to the development of acidosis.

6. List three problems caused by acidosis. Explain how each problem listed is caused by acidosis.

7. Give two methods to prevent enterotoxemia.

8. What causes stiff lamb disease?

9. Describe accelerated lambing.

10. Define flushing/feeding management. Give two purported benefits to using flushing rations.

REFERENCES

Cole, H. H., & Cupps, P. T. (1997). Reproduction in domestic animals (3rd edition). New York: Academic Press, Inc.

Garner, M. R., Hay, A. G., Guard, C. L., & Russell, J. B. (2003). Bovine laminitis and Allisonella histaminiformans. In Proceedings Cornell nutrition conference. East Syracuse, NY.

Gunn, R. G. (1983). The influence of nutrition on the reproductive performance of ewes. In Sheep production. W. Haresign, England: Butterworth.

Kaufmann, W., Hagemeister, H., & Dirksen, G. (1980). Adaptation to changes in dietary composition, level and frequency of feeding. In: Digestive Physiology and Metabolism in Ruminants, editors Y. Ruckenbusch and P. Thivend. Westport, CT: AVI Publishing Co.

Nagaraja, T. G., & Chengappa, M. M. (1998). Liver abscesses in feedlot cattle: A review. Journal of Animal Science. 76, 287-298.

National Research Council. (1980). Mineral tolerance of domestic animals.Washington, DC: National Academy Press.

Owens, F. N., Secrist, D. S., Hill, W. J., & Gill, D. R. (1998). Acidosis in cattle: A review. Journal of Animal Science. 76, 275-286.

Schwartzkopf-Genswein, K. S., Beauchemin, K. A., Gibb, D. J., Crews, D. H., Jr., Hickman, D. D., Streeter, M., & McAllister, T. A. (2003). Effect of bunk management on feeding behavior, ruminal acidosis and performance of feedlot cattle: A review. Journal of Animal Science. 81, E149-E158.

Snowder, G. D., & Glimp, H. A. (1991). Influence of breed, number of suckling lambs, and stage of lactation on ewe milk production and lamb growth under range conditions. Journal of Animal Science. 69, 923-930.

Thompson, J. M. & Meyer, H. Undated. Body Condition Scoring of Sheep. Retrieved October, 2004 from: http:// oregonstate.edu/dept/animal-sciences/bcs.htm
COPYRIGHT 2006 Delmar Learning
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2006 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Tish, David A.
Publication:Animal Feeds, Feeding and Nutrition, and Ration Evaluation
Geographic Code:1USA
Date:Jan 1, 2006
Words:5500
Previous Article:Chapter 19 Dairy ration formulation.
Next Article:Chapter 21 Sheep ration formulation.
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters