Comparisons of heat loss from young cockerels by direct measurement and by indirect assessment involving body analysis

Synopsis Young cockerels were fed diets containing normal or relatively low concentrations of protein, and heat loss was measured either directly in a gradient layer calorimeter or indirectly by subtracting the gain in body energy from the metabolisable energy eaten. Direct measurement of heat loss daily yielded information not easily obtainable by body analysis techniques. Expected differences in energy lost as heat, complementary to differences found in tissue energy gain between birds on control and low‐protein diets, could be demonstrated on occasion by the indirect body analysis technique but not by the direct method. The latter method of estimating total heat loss tended to give lower values than the indirect method, by about 3 per cent in one experiment and 12 per cent in another. Although fast‐growing Chunky Chick hybrids consistently ate more food energy per unit weight than slower‐growing White Link hybrids, daily heat loss from the Chunky Chick appeared to be no greater than from the White Link and so energy utilisation was more efficient and growth rate greater in the case of the Chunky Chicks.