Sheep Extension Program

Montana Farm Flock Sheep Production Handbook Nutrition Part 1 — Section 5 of 7

By Rodney Kott, Extension Sheep Specialist, Animal & Range Sciences Department, Montana State University

Ultimately, the production of sheep is controlled by their economic efficiency in converting available feed resources into products of economic value. Productivity of the pasture, rangeland or forage crop will largely dictate the maximum levels of productivity the sheep producer can achieve.

Supplying the nutrient needs of a sheep represents the single, largest expense in the total cost of raising sheep. Because of this, a solid understanding of nutrition is necessary in order to minimize the annual cost of production yet maintain optimum production levels. The National Resource Council (NRC) established a fairly precise set of nutrient requirements for sheep for various stages of production and with different levels of productivity. These resources represent the most current understanding of the needs of sheep for specific nutrients such as energy, protein, minerals and vitamins in order to meet clearly defined production objectives. Requirements presented in these publications should be used as guidelines and not as rigid standards. The most common misinterpretation of these recommendations is that each production system must provide for these nutrient levels and weight changes. Deviations from this system are possible, however, short-term deviations must be compensated for over the course of the entire production cycle if optimum production is to be maintained.

Nutrient needs

The nutrients of primary importance in sheep are: water; energy as measured by total digestible nutrients (TDN), metabolizable energy (ME) or net energy (NE), protein either crude or digestible protein; minerals and vitamins.

Water

Water, although often overlooked, is one of the most important nutrients required for life. An adequate supply of clean, fresh water is essential to efficient sheep production. Inadequate water consumption will reduce feed and forage intake and compromise performance. In fact, a deficiency of water will cause death much faster than a deficiency of any other nutrient. Daily water consumption of ewes will vary from .72 gallons during the cold winter months, to 1.5 gallons during the late winter months when temperatures begin rising, to as high as 2.2 gallons when sheep consume dry forage such as saltbush. In some instances ewes can meet their winter water needs by eating snow.

Energy

Insufficient energy probably limits performance of sheep more than any other nutritional deficiency. It may result from inadequate amounts of feed or from feeds of low quality. The energy requirements of a ewe varies greatly with her stage of production.

Adequate amounts of energy are extremely important during late gestation and during early lactation. Energy shortages are often complicated by protein or mineral deficiencies. A sheep's energy needs can, in most instances, be supplied by feeding good quality pasture, hay or silage. Additional energy is generally needed immediately before and after lambing, in conditioning ewes and rams for breeding and in finishing lambs. Grains such as barley, corn, wheat, oats and milo are generally used to raise the energy level when supplementation is necessary. During lactation a ewe's metabolic energy requirements can at least partially be met by breaking down body fat reserves.

Protein

In most situations the amount of protein supplied in the diet is more critical than protein quality. Ruminants have the ability to convert low quality protein sources to high quality proteins by bacterial action. Protein available for digestion in the small intestine thus consists of microbial protein and feed protein that has escaped microbial breakdown in the rumen. Microbial protein synthesis is sufficient to supply the sheep’s protein needs provided adequate precursors are available, except during lactation in high milk producing ewes and in very young lambs when rumen activity is limited.

Green pastures, when comprising the complete diet, will provide adequate protein for most classes of sheep. When ranges are mature and bleached, or have been dry for an extended period of time, and when grass hay or high grain rations are fed, additional protein may be needed. High protein feeds are often added to creep rations because they are usually extremely palatable and stimulate appetite and digestive activity. In isolated instances, it may be beneficial to feed proteins with a high bypass value.

There are 15 minerals that have been demonstrated to be essential in sheep nutrition. They are: sodium, chlorine, calcium, phosphorus, magnesium, potassium, sulfur, cobalt, copper, iodine, iron, manganese, molybdenum, selenium and zinc. Although relatively precise requirements have been published for the different minerals, it should be recognized that in practice the true dietary requirements vary greatly depending on the nature and amount of these and associated minerals in the diet. A number of mineral balances (e.g. calcium and phosphorus, copper to molybdenum, selenium and vitamin E) must be considered when establishing the actual requirements under specific conditions.

Most of these are met under normal grazing and feeding habits. In many situations poor animal performance is attributed to a mineral deficiency, when in fact it is due to something else. Under normal grazing situations minerals most likely to be deficient are salt (sodium chloride) and phosphorus. Selenium has been shown to be deficient in certain areas of Montana and the U.S.

Trace mineralized salt is usually fed to sheep free choice. However, care should be taken to be sure that the trace mineral mixtures are specifically developed for sheep and do not contain the high levels of copper commonly found in beef, dairy, swine and poultry trace mineral mixes. Most trace mineralized salt mixtures formulated for sheep provide 8 of the 15 essential minerals (Na, Cl, I, Co, Fe, Mn, and Zn). The minerals that are normally provided in sufficient amounts in natural feedstuffs include K, Mg, Fe, Cu and Mn. It is important to note that trace mineral salt does not usually supply phosphorus.

Salt: Salt serves many functions in the body. When deprived of salt, sheep will consume less feed and water. As a general rule, sheep producers should provide supplemental salt to their sheep. Salt is generally fed to ewes at the level of .25 to .4 ounces per head per day. It can be fed "free choice" or added to the feed mix.

Calcium and Phosphorus: Most pastures, hays and other forages contain adequate levels of calcium for sheep and thus calcium supplementation is seldom necessary. However, grains are somewhat deficient in calcium and thus supplementation is often beneficial when sheep consume diets that consist primarily of grains or corn silage.

Mature pasture and range forage is often deficient in phosphorus. Grains, however, are relatively high in phosphorus content. Since in most situations a high percentage of a sheep’s diet will consist of roughage or pasture, phosphorus supplementation is often beneficial. The most desirable way to supply additional phosphorus, when needed, is by adding it directly to the feed mix. This, however, is not always practical or feasible. It is sometimes more convenient to supplement the sheep’s diet with a high-phosphorus mineral mix.

The ratio between calcium and phosphorus must be considered when balancing sheep rations. Although ratios of 5 or 6 to 1 (calcium to phosphorus) seem satisfactory, a ratio of 2:1 is ideal for most sheep rations. Feedlot lambs or growing rams fed diets high in grain are prone to urinary calculi. In these situations the incidence of urinary calculi can be reduced by raising the calcium to phosphorus ratio to 3 or 4 to 1.

Copper: There is a delicate balance between the copper requirement and copper toxicity in sheep. In most cases, sheep can meet or exceed their dietary requirements for copper from normal feeds and thus do not require additional copper. Sheep are more susceptible to copper toxicity problems than most other livestock species. Errors in feed mixing frequently result in death due to copper toxicity.

Copper requirements of sheep are dependent on dietary and genetic factors and, therefore it is almost impossible to develop a set of well defined requirements. In fact, it has been shown that dietary amounts of copper that are adequate in one situation may be deficient in another and possibly toxic in a third situation. Concentration of molybdenum is a major dietary factor affecting the ewes copper requirement. Molybdenum forms an insoluble complex with copper which reduces its absorption thus increasing the dietary levels needed to meet requirements. Also Merino breeds of sheep generally are less efficient in absorbing copper from feedstuffs than British breeds of sheep.

Although it is impossible to give the exact requirements and toxic levels, the recommended copper allowance is 7 to 10 mg/kg DM when the Molybdenum content in the diet is below 1.0 mg/kg up to about 14-20 mg/kg when molybdenum content is above 3.0 mg/kg. It should be stressed that these are just guidelines and may vary drastically from situation to situation. When selecting a trace mineral mix for sheep, it is generally recommended to choose one that contains no or minimal copper. Mineral mixes providing over 4 mg of copper per ewe per day should be avoided.

Selenium:In sheep there is a very narrow range between the amount of selenium that is required in the diet and that which will be toxic. Diets containing less than .1 ppm selenium are deficient while those containing over 2 ppm are above the maximum tolerable level. White Muscle Disease in lambs results from a deficiency of selenium and possibly vitamin E. A marginal deficiency in selenium can result in reduced reproductive performance and increased lamb mortality. This deficiency can be prevented by giving injections of a commercial product containing both selenium and vitamin E. Selenium and or vitamin E can also be added to the entire ration, supplement or salt-mineral mix of sheep. Probably the most practical and effective way of supplying selenium to sheep is by feeding a salt-mineral mix containing selenium. There are many excellent ones on the market. Do not try to mix your own. When supplementing selenium either by feeding or injection), producers should follow the manufacturer’s or veterinarian’s recommendations very closely. There may be some instances in sheep nutrition where, "If a little is good, a lot is better." However, "a lot" of selenium can be lethal.

Vitamins

Mature sheep require all of the fat-soluble vitamins: A, D, E and K. They usually do not require the B vitamins since these are synthesized in the rumen. Normally, the forage and feed supply all of the vitamins in adequate amounts. Vitamin A can become deficient if sheep have been grazing on dry or winter pastures for an extended period of time. Sheep, however, store Vitamin A for a considerable time, and if ewes have been on green forage or have had access to high-quality legume hay, Vitamin A is usually not deficient. Vitamin D deficiencies may develop in confined sheep. Sheep raised outside will usually have sufficient vitamin D as sunlight builds a store of this vitamin in the body.