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Interrelationships among Energy Input, Body Size, Age and Body Composition of Sheep¹

Department of Animal Science, Cornell University, Ithaca, New York

Interactions of age, body weight and energy intake on the proximate chemical composition and energy value of the body were examined in 26 Shropshire, male-castrate sheep. Body weight at a given age was manipulated by imposing on a given animal one of two levels of energy input (averaging 278 and 421 kcal of gross energy/1 kg empty-body weight ^0.73 per day). The amounts of body components at a given age were greater in sheep receiving the high intake of energy than in those supplied the low level. The relationships between the body components and body weight, however, were not different for the two energy input levels. Thus, energy input, within the range studied, did not influence body composition in a manner independent of its effect on body mass. In animals containing less than 31% of fat, the amounts of body components increased linearly with increasing body weight; above this concentration of fat, the weights of water and protein increased at decreasing rates and the amounts of fat and energy increased at increasing rates, as body weight increased. The overall best fit of the relationships between the body components and body weight was provided by the model, Y = a X^b. For these relationships, the R² values for the predictands other than ash ranged from 0.939 to 0.982. The use of age in addition to body weight as the predictors increased the R² values by only 0.002 to 0.019 over those computed between body weight alone and the various predictands. Thus, body composition in sheep was not related to prior energy intake, only slightly associated with age, but was chiefly associated with body weight.

² The data reported here are a part of those presented in the M.S. degree Thesis by J. H. Burton to the Graduate School, Cornell University, 1967.

Manuscript received 21 October 1968.