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Heat of Combustion Values of the Protein and Fat in the Body and Wool of Sheep^1,2,

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

The heat of combustion values of protein and fat were determined in the ash-free, dry matter of the bodies of 63 sheep, and of the wool of 45 sheep. As a consequence of the ranges in age at the time of slaughtering and the dietary treatments imposed, the animals represented a wide range in body composition. After each animal was shorn and slaughtered, the ingesta-free body was separated into 4 parts, consisting mainly of the blood, viscera, hide, and carcass. The mean calorific values (kcal/g) of the protein and fat, respectively, in the various body parts were as follows: blood, 5.854 ± 0.052 and 7.435 ± 0.052; viscera, 5.428 ± 0.057 and 9.312 ± 0.057; hide, 5.458 ± 0.086 and 9.305 ± 0.086; and carcass, 5.327 ± 0.068 and 9.424 ± 0.068. For the total, ingesta-free body, the calorific values were 5.379 ± 0.051 kcal/g of protein and 9.405 ± 0.051 kcal/g of fat. As the result of the manner by which they were derived, these values represent the calorific value of the composite body proteins and lipids. As a consequence, these values are more accurate for use in studies involving the metabolism and storage of energy than are the older values which are based chiefly on the analysis of body (generally muscle) proteins and body fats purified to various degrees. Although the calorific value of fat (9.405 kcal/g) representing the total body was only slightly lower than the commonly used value (9.5 kcal/g), the calorific value of protein representing the total body (5.379 kcal/g) was considerably lower than that (5.7 kcal/g) which is generally used. The calorific value of wool protein was found to be 5.609 ± 0.0023 kcal/g and that of wool fat was 9.741 ± 0.0035 kcal/g. Since wool protein contained 16.85% of nitrogen, the obligatory factor for converting the percentage of nitrogen to the percentage of protein is 5.933.

² The data presented here are a part of those presented in the Ph.D. degree thesis by O. L. Paladines to the Graduate School, Cornell University, 1963.

³ Recipient of Organization of American States scholarship (1960–62) and Rockefeller Foundation fellowship (1962–63); present address: Inter-American Institute of Agricultural Sciences, Turrialba, Costa Rica.

⁴ Present address: Grootfontein College of Agriculture, Middelburg, South Africa.

Manuscript received 5 August 1963.