Economical and efficient production of sheep for meat, wool, milk, show, and pets is contingent on proper feeding, husbandry practices, and health care. All of these are influenced by dietary intake. Maintenance of breeding animals, a high percentage of the lamb crop weaned, lamb growth, optimal weaning weights, and a heavy fleece weight and fleece quality are important to production efficiencies.
Nutritional requirements for maintenance, reproduction, growth, finishing, and wool production are complex because sheep are maintained under a wide variety of environmental conditions; however, attempts should be made to ensure each production unit or individual sheep has adequate nutrient intake to be healthy and productive.
An adequate diet for optimal growth and production must include water, energy (carbohydrates and fats), protein, minerals, and vitamins. Under field conditions of particular stress, additional nutrients may be needed. For detailed nutrient requirements for sheep, refer to the most current Nutrient Requirements of Small Ruminants, published by the National Academies of Sciences, Engineering, and Medicine.
Water Requirements of Sheep
A clean, fresh, easily accessible source of water should be available at all times. As a minimum requirement in temperate environments, the usual recommendations are approximately 3.8 L (1 gallon) of water/day for ewes on dry feed in winter, 5.7 L (1.5 gallon)/day for ewes nursing lambs, and 1.9 L (0.5 gallon)/day for finishing lambs.
In many range areas, water is the limiting nutrient. For best production, all sheep should have their water availability monitored daily during all weather conditions. However, the cost of supplying water often makes it economical to water range sheep (provide sheep with drinking water in their grazing area) every other day. When soft snow is available, range sheep do not need additional water except when dry feeds such as alfalfa hay and pellets are fed. If the snow is crusted with ice, the crust should be broken to allow access. Still, when possible, sheep should have unlimited access to fresh, clean water.
Energy Requirements of Sheep
Much of a sheep's diet depends on grass or other forages that can be sparse or of poor quality, so the provision of adequate dietary energy is important. Poor-quality forage, even in abundance, may not provide sufficient available energy for maintenance and production. The total energy required in the sheep's diet varies according to factors such as production stage, age, and season. Typically, the energy requirement at maintenance can be met with feeds containing at least 50% total digestible nutrients (TDN). The energy requirement of ewes is greatest during the first 8–10 weeks of lactation. Because milk production declines after this period and lambs have begun foraging, the ewes' energy requirement is then decreased to prelambing levels.
The most efficient and accurate way to assess energy adequacy in sheep is to assess and record body condition using an objective 1–5 scoring system, with 1 being extremely thin and 5 being extremely obese. The body condition score is determined by palpating the amount of fat covering on the lumbar spinous processes and transverse processes. Most healthy, productive ewes will have a score of 2–3.5. Sheep with a score of 1–2 should be examined and fed to attain a higher score, whereas those with a score > 3.5 should be fed less. Dietary changes should be made slowly, and an abrupt decrease in total energy intake should always be avoided, particularly in middle to late gestation.
More details on body condition scoring are available from the University of Arkansas Cooperative Extension Service, Agriculture Victoria, and the Farm Advisory Service of Scotland, among others.
Protein Requirements of Sheep
Good-quality forage and pasture generally provide adequate protein for mature, nongrowing, nonlactating sheep. A minimum of 7% dietary crude protein is needed for maintenance in most sheep. Protein requirements depend on the stage of production (growth, gestation, lactation, etc) and the presence of certain diseases (internal nematode parasites, dental disease, etc). If available forages are unable to supply adequate dietary crude protein, protein supplements, such as oilseed meals (cottonseed meal, soybean meal) or commercially blended supplements, should be fed to meet nutrient requirements. Protein also should be fed to meet requirements. Excess protein feeding can be beneficial in cases of excessive internal parasite burdens but also results in increased production costs and may result in higher incidence of disease (eg, heat stress, pizzle rot).
While essential and nonessential amino acid requirements are generally met by microbes in the rumen, some amino acids may be considered occasionally limiting to sheep and wool production. Wool production is supported by sulfur-containing amino acids such as methionine and cysteine, which comprise a large portion of keratin, the primary protein in wool. Methionine is also important for a range of other processes, such as milk production and growth. Lysine, histidine, leucine, isoleucine, and valine are important as well for other aspects of production.
Sheep can convert nonprotein nitrogen (such as urea, ammonium phosphate, and biuret) into protein in the rumen, although they may do so less efficiently than beef cattle. This source of nitrogen can provide at least a part of the necessary supplemental nitrogen in high-energy diets with a nitrogen:sulfur ratio of 10:1. In lamb-finishing diets, adding alfalfa, approved growth stimulants, and a source of fermentable carbohydrates (eg, ground corn, ground milo) enhances nitrogen utilization.
Mineral Requirements of Sheep
Sheep require the major minerals sodium, chlorine, calcium, phosphorus, magnesium, sulfur, and potassium, plus trace minerals, including cobalt, copper, iodine, iron, manganese, molybdenum, zinc, and selenium. Trace mineralized salt provides an economical way to prevent deficiencies of sodium, chlorine, iodine, manganese, cobalt, copper, iron, and zinc. Selenium should be included in rations, mineral mixtures, or other supplements in areas where soils are deficient.
Sheep diets usually contain sufficient potassium, iron, magnesium, sulfur, and manganese. Of the trace minerals, iodine, cobalt, and copper status in ewes are best assessed via analysis of liver biopsy tissue. Zinc adequacy can be assessed from the careful collection of nonhemolyzed blood placed in trace element–free collection tubes. Selenium status is easily assessed by collection of whole, preferably heparinized, blood.
Salt Requirements of Sheep
In the US, except on certain alkaline areas of the western range and along the seacoast, sheep should be provided with ad lib salt (sodium chloride). Sheep need salt to remain thrifty, make economical gains, lactate, and reproduce. Mature sheep will consume approximately 9 g (0.02 pounds) of salt daily, and lambs, half this amount. Range operators commonly provide 225–350 g (0.5–0.8 pounds) of salt/ewe/month. Salt as 0.2–0.5% of dietary dry matter is usually adequate.
Calcium and Phosphorus Requirements of Sheep
Generally, the leafy parts of plants are relatively high in calcium and low in phosphorus, whereas the reverse is true of the seeds or grain. Legumes, in general, have a higher calcium content than grasses. As grasses mature, phosphorus is transferred to the seed (grain). Furthermore, the plant's phosphorus content is influenced markedly by the availability of phosphorus in the soil. Therefore, low-quality pasture devoid of legumes and range plants tends to be naturally low in phosphorus, particularly as forage matures and seeds fall.
Sheep subsisting on mature brown summer forage and winter range sometimes develop a phosphorus deficiency. Sheep kept on such forages or fed low-quality hay with no grain should be provided a phosphorus supplement (ie, defluorinated rock phosphate) added to a salt–trace mineral mixture. Because most forages have a relatively high calcium content, particularly if there is a mixture of legumes, diets usually meet maintenance requirements for this element. However, when corn silage or other cereal grain feeds are fed exclusively, ground limestone should be fed daily at the rate of 9–14 g (0.02–0.03 pounds).
Sheep seem to tolerate a wide range of calcium:phosphorus ratios as long as their diets contain more calcium than phosphorus. However, an excess of phosphorus may be conducive to development of urinary calculi or osteodystrophy. A calcium:phosphorus ratio of 1.5:1 is appropriate for feedlot lambs. For pregnant ewes, the diet should contain ≥ 0.18% calcium and for lactating ewes, ≥ 0.27% calcium. A dietary content of 0.2–0.4% calcium is considered adequate, as long as the calcium:phosphorus ratio is maintained between 1:1 and 2:1.
Iodine Requirements of Sheep
Occasionally, the iodine requirements of sheep are not met in the natural diet, and thus iodine supplements must be fed. Goitrogenic substances are found in many types of plants (eg, Brassica spp) and interfere with the use of iodine by the thyroid. Regions naturally deficient in iodine are found throughout the western US, in the Great Lakes area, and in other parts of the world. Iodine deficiency (manifested as goiter in the adult and as lack of wool and/or goiter in lambs) can be prevented by feeding stabilized iodized salt to pregnant ewes. The young of iodine-deficient ewes may be aborted, stillborn, or born with goiters. Diets containing iodine at 0.2–0.8% ppm are usually sufficient, depending on the animals’ level of production (maintenance/growth, lactation, etc).
Cobalt Requirements of Sheep
Sheep require approximately 0.1 ppm of cobalt in their diet. Cobalt-deficient soils are found in North America but are relatively rare compared with other parts of the world. Normally, legumes have a higher cobalt content than grasses. Because cobalt levels of the feedstuffs are seldom known, a good practice is to feed trace mineralized salt that contains cobalt.
Copper Requirements of Sheep
Pregnant ewes require approximately 5 mg of copper (Cu) daily, which is the amount provided when the forage contains ≥ 5 ppm. However, the amount of copper in the diet necessary to prevent copper deficiency is influenced by the intake of other dietary constituents, notably molybdenum (Mo), inorganic sulfate, and iron. High intake of molybdenum, in the presence of adequate sulfate, increases copper requirements. Because sheep are more susceptible than cattle to copper toxicity, care must be taken to avoid excessive copper intake. Toxicity may be produced in lambs being fed diets with 10–20 ppm of copper, particularly if the Cu:Mo ratio is > 10:1. The Cu:Mo ratio should be maintained between 5:1 and 10:1.
Selenium Requirements of Sheep
Selenium is effective in at least partially controlling nutritional muscular dystrophy. Areas east of the Mississippi River and in the northwestern US appear to be low in selenium. The dietary requirement for sheep is approximately 0.3 ppm. Providing selenium-containing mineral mixture may prevent selenium deficiency if animals are allowed free access. Levels of 7–10 ppm or higher may be toxic.
Zinc Requirements of Sheep
Growing lambs require approximately 30 ppm of zinc in the diet on a dry-matter basis. The requirement for normal testicular development is somewhat higher. Classic zinc deficiency (parakeratosis) is more common in other small ruminants (goats, llamas, alpacas) but is occasionally encountered in sheep, particularly those fed excessive quantities of dietary calcium (legumes).
Vitamin Requirements of Sheep
Sheep diets usually contain an ample supply of vitamins A (provitamin A), D, and E. Under certain circumstances, however, supplements may be needed. The B vitamins and vitamin K are synthesized by the rumen microorganisms and, under practical conditions, supplements are unnecessary. However, sheep can develop polioencephalomalacia from aberrations in ruminal thiamine metabolism, secondary to altered ruminal pH and/or microflora content.
Sheep synthesize vitamin C in their livers. On diets rich in carotene, such as high-quality pasture or green hays, sheep can store large quantities of vitamin A in the liver, often sufficient to meet their requirements for up to 6 months.
Sheep derive vitamin D2 from ingesting sun-cured forage, and they synthesize vitamin D3 in skin from exposure to UV light. When prolonged cloudy weather or confinement rearing decreases skin exposure to sunshine, or when vitamin D2 content of the diet is low, vitamin D requirements in sheep may not be met. The vitamin D requirement is increased when amounts of either calcium or phosphorus in the diet are low or when the ratio between them is wide. Dietary modifications should be made slowly and cautiously to avoid vitamin D toxicity. Fast-growing lambs kept away from direct sunlight or maintained on green forages (high carotene) during the winter months (low irradiation) may show clinical signs of vitamin D deficiency. Normally, sheep on pasture seldom need vitamin D supplements.
The major sources of vitamin E in the natural diet of sheep are green feeds and the germ of seeds. Because vitamin E is poorly stored in the body, a daily intake is needed. When ewes are being fed poor-quality hay or forage, supplemental vitamin E may improve production, lamb weaning weights, and colostrum quality. Vitamin E deficiency in young lambs may contribute to nutritional muscular dystrophy if selenium intake is low.
Key Points
The amounts of water, energy, protein, vitamins, and minerals in a sheep's diet depend on numerous factors, such as their production stage, their age, and the season.
Generally, as lamb and wool production increase, the corresponding increase in nutritional requirements needs to be met with additional feed and supplements.
Nutritional status can be monitored through observation, production measures, and body condition scoring to make necessary adjustments to the diet and ensure all nutritional requirements are being met.
For More Information
Kott R. Montana farm flock sheep production handbook: nutrition. Montana State University Sheep & Wool Extension Program.
Filley S. Nutrient requirements of sheep. Oregon State University Extension Service.
Nutrition. Meat & Livestock Australia.
