Sheep have higher protein requirements per unit of weight than many other ruminants because of the extra protein needed for wool growth. Protein within the sheep’s body is in a constant state of flux with degradation and synthetic activities occurring simultaneously. Usually, the quality of protein is less important in the diet of mature sheep than is the quantity. Regardless of the type of protein fed, some of it will be degraded by the ruminal-reticular microorganisms and synthesized into high-quality, microbial protein. In turn, microbial protein is enzymatically digested in the lower GIT of sheep to yield amino acids for absorption. Only under very high-production conditions (e.g., high rate of growth and milk production) will protein from microbial sources be inadequate. In these cases, supplementing with bypass (low rumen degradable) protein sources may increase productivity.

Requirements for protein, like energy, are affected by the stage and level of production. Protein requirements of ewes are significantly increased during late gestation and lactation when compared with early gestation, breeding, and maintenance stages of production. The protein requirement is highest in youngest lambs because weight gain contains a higher proportion of protein (lean tissue) and less fat than in older lambs. As sheep grow to maturity, protein requirements decrease to maintenance levels. Variation from maintenance requirements is then a function of the different stages and levels of production.

Soybean, cottonseed, sunflower, linseed, and peanut meals contain 35 to 50 percent protein and are excellent protein supplements for sheep. Blood, feather, fish, poultry by-product, and meat meals are high-quality supplements that contain 50 to 90 percent protein. Legume hays, harvested at early to midbloom stage of maturity, are intermediate in protein content (15 to 25 percent). When fed as a complete diet, these hays will provide adequate protein for mature ewes and rams at maintenance and for yearling replacement stock. Grains are relatively low in protein (8 to 13 percent) and should be fed as an energy source rather than for protein. When used in growing-finishing diets, they require supplementation with the above-mentioned supplements or legume hays if optimum performance is to be attained.

Protein feedstuffs are more expensive than energy sources on a “weight for weight” basis. Therefore, overfeeding protein has a greater economic impact than overfeeding energy. If protein is overfed, the excess will be used inefficiently for energy, which is an expensive process as compared to feeding energy feedstuffs for energy.

Urea is probably the most inexpensive source of dietary nitrogen for sheep. It is fed in the form of “nonprotein nitrogen,” but converted to microbial protein in the rumen-reticulum. The microbial protein, then, is enzymatically digested in the lower GIT. Consumption of urea requires simultaneous consumption of soluble carbohydrates. The following guidelines should be followed for use of urea in sheep diets:

• Do not mix more than 1 percent of the total diet or 3.0 percent of the concentrate portion. Urea crude protein equivalent should not exceed one-third of the total dietary protein.
• Urea can be added to silage at the rate of 1.0 percent at the time ensiling.
• Do not use in creep diets because of reduced intake of complete diet or potential urea toxicity.
• Introduce into the diet gradually over a two-three-week period.
• Always mix thoroughly with other dietary ingredients of the same physical form to prevent ingredient separation.
• Feed urea-containing diets at regular intervals, preferably self-fed.

Other protein supplements can be self-fed or hand-fed daily or at two- to three-day intervals. The most economical form of hand-fed supplements is pellets or cake. Protein blocks, while more expensive than meal or pellets, may save labor, can be used to supplement pastures or ranges, and may be used as a management tool to improve pasture or range utilization. Blocks are available in varying degrees of hardness to help regulate consumption. However, blocks that are too hard may reduce consumption as well as result in broken teeth.

Intake of protein supplements (meal form) that are self-fed can be regulated by addition of 10 to 25 percent salt. When using salt to limit consumption, an adequate water supply must be available. Precise regulation of intake by this method is difficult, but it may reduce labor requirements.