Temperature, humidity and wind velocity affect energy requirements for ewe maintenance. The length and density of the fleece determine the insulating properties of the wool cover. Thus, wool cover governs how much effect the climate will have on the dietary energy requirements. The critical minimum temperature for a freshly shorn sheep fed at maintenance level is 50F. The same sheep fed the same ration but with 2.5-inch fleece has a minimum critical temperature of 28F. Wind velocity and humidity levels, in combination with low temperatures, markedly increase body heat losses and thereby increase energy requirements, regardless of wool cover.
High temperatures along with high humidity also increase maintenance requirements. With each 1-degree increase in body temperatures above normal, the metabolic rate increases about four percent. Wool serves as a protectant from heat, particularly against solar radiation. Body coat both reflects and radiates heat from the fiber tips and insulates the body surface. For example, temperatures of up to 150F at the fleece tip of full-fleeced sheep have been measured without showing an increase in the temperature at skin surface. Humidity levels exert a greater effect on energy requirements than do absolute ambient temperatures. The higher the humidity level at a given temperature, the harder it becomes for animals to dissipate body heat. This extra effort in turn increases the energy required to maintain normal bodily functions. Fatter sheep are more susceptible to high environmental temperature and humidity stress than those in normal body condition.
A nutrient deficiency during snowstorms is usually associated with cold temperatures and is often complicated by high wind velocity and wet fleeces. Again, the most critical nutrient that is required in this situation is energy. As much as 40% additional energy above maintenance may be needed to maintain body temperature when environmental temperatures reach 10F above to 10F below freezing. High quality hay may be the preferred nutrient source, since it has a higher heat increment than concentrates and is easier for sheep to consume on isolated, snow-covered feeding grounds. If winter or early spring lambing is practiced, ewes will also have higher late gestation nutrient requirements. Attempts to accommodate their requirements under these conditions by suddenly providing extra concentrates can cause pregnancy toxemia, abortion or both.
Shearing several weeks or month prior to periods of potential climatic stress is often desirable for management purposes. Producers lambing in early spring, for example, like to shear 2-4 weeks prior to lambing. However, ewes should be moved to a protected area, if needed, for 2-3 weeks after shearing. Most shearers and producers use raised combs that leave approximately .25 inches of wool when shearing at these times. Fleece lanolin and soil contamination will normally combine to provide an adequate protective crust on the fleece 2-3 weeks after shearing if this length of wool is left at shearing. On the other hand, close or slick shorn sheep may be susceptible to climatic stress if the weather turns cold. Also, slick shorn sheep are more susceptible to heat stress immediately after shearing if ambient temperatures reach 80-85F and the sheep are without shade.
Travel distance and land topography can significantly affect nutrient requirements, especially energy. Although the nutrient requirements take into account normal exercise of grazing sheep, additional running, climbing, fear, or excitement may increase energy requirements because of increased bodily heat production and its need for dissipation.
Amount of exercise may be a function of forage availability. As forage availability decreases, exercise obviously increases, as do nutrient requirements. Supplementation will be required to meet higher nutrient needs where forage availability is limited.
Yearlings tend to have a higher maintenance energy requirement than adult sheep. This difference may be due to the need to support a larger proportion of lean body mass in the younger animals, while the adult sheep's fat tissue requires less energy to maintain. Greater visceral mass and organ mass in proportion to empty body weight of younger sheep also requires more energy for maintenance. On the range, younger ewes are less experienced than older ewes and may spend more time in travel while grazing until they learn the preferred plant age, species and plant communities. As ewes age beyond five to six years, it becomes increasingly difficult for them to maintain the level of activity of younger ewes in their grazing activities. This is especially true in the more vigorous desert and alpine range conditions. Older ewes however can often be managed as a separate group under improved foraging conditions and be expected to be productive for additional years.
Body fat must be supported by energy from the diet in the same manner as lean body tissue. Sheep producers should, therefore, know the normal body weight of their ewe flock, independent of fat or excessive conditions, when making decisions on nutritional management. Under normal production conditions, sheep may experience periods of over-nutrition and under-nutrition. Over-nutrition may be acceptable if the body fat stored is used at a later time when ewes have high nutrient demands (late gestation, lactation). Under-nutrition may be acceptable during periods of low nutrient demand (maintenance, early gestation) if ewes are allowed to recover before higher nutrient demand periods occur (breading, late gestation, lactation).
Body Condition Scoring of Sheep
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This Web page was created by Yusaf Paracha and was last updated on April 19, 1999.