Effect of Environment on Nutrient Requirements of Domestic Animals (1981) / Chapter Skim
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SHEEP
SHEEP
Pages 85-95
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From page 85... ...
For a large lamb in the same condition, metabolism would match heat loss at approximately 4°C. Obviously, survival during cold is highly variable, depending on both the animal's ability to increase heat production and aspects of the environment affecting effective ambient temperature (EAT)
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From page 86... ...
of about 25°C, but LCT is estimated as low as -20°C in similar fleeced animals (Blaxter, 1967; Webster et al., 1969~. Calculation of lower critical temperature indicates that increased intake and the concurrent increase in heat production reduces LCT as much as 20°C from ad libitum feeding to fasting.
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From page 87... ...
Although information relating diet digestibility to heat stress is not in total agreement, most data tend to support the hypothesis that digestibility is increased during heat stress. Some believe this results from decreased voluntary intake rather than from a direct effect of increased EAT.
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From page 88... ...
These findings suggest an apparent reduction in external insulation and result in increased rate of sensible heat loss when measured at a given thermal gradient. Use of effective ambient temperature measures such as wind-chill temperature (Ames and Insley, 1975)
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From page 89... ...
amount of insulation provided by tissue, fleece, and air. These factors can be used to estimate rate of heat loss, and therefore maintenance energy requirement for animals exposed to cold, by the following equation: MEm = a\;V1~75 + b l where MEm = metabolizable energy for maintenance corrected for effective temperature (kcal ME/day)
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From page 90... ...
The value of heat increment during cold has been mentioned previously, and, while this may prove valuable, it should be understood that heat increment for each unit of weight of roughages and concentrates is similar. However, heat increment is a higher percentage of digestible energy for roughages as compared with concentrates, so that calories supplied by the heat increment of a roughage may be less expensive than those from a con TABLE 25 Comparison of Measured and Estimated Heat Loss (kcal/m2/ day/°C)
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From page 91... ...
The magnitude of this advantage is dependent upon relative ingredient prices, magnitude of cold, and the effect of cold on intake. ENERGY REQUIREMENT DURING HEAT STRESS Expected increases in heat production during heat exposure of sheep have been reported, but little quantification of increased energy needs is available.
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From page 92... ...
. The frequently used protein-to-energy ratio for formulation of animal diets is not appropriate for describing diets during thermal stress when maintenance energy requirement and intake vary unless only protein and calorie values surplus to maintenance are used to calculate a ratio.
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From page 93... ...
conducted growth and efficiency studies for shorn lambs exposed to a wide range ~ - 5 to 35°C) of ambient temperatures.
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From page 94... ...
studied the effect of simulated altitude on sheep and found no difference in heat production or heat increment values when oxygen concentration in air was 150 ml/liter compared to 200 ml/liter. Confinement rearing of sheep has been estimated to reduce energy requirements by 30 percent (Parker, 19761.
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From page 95... ...
Responses of sheep to thermal stress in terms of intake, maintenance energy requirement, and rate of performance are typical. Nutrient adjustments for changes in voluntary intake, energy adjustments for cold stress, and protein adjustments for differences in thermally induced changes in rate of growth are presented but are based on limited research data.
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