The utilization of the metabolizable energy of diets of different protein content by the milk-fed lamb

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Abstract
SUMMARY: Nineteen male cross-bred lambs, aged between 2 and 5 days, were allotted to each of three dietary treatments for an experimental period of 3 weeks. The protein contents of the diets (on a dry-matter basis) were 12·0% (diet A), 28·5% (diet B) and 45·5% (diet C). The diets were fed as artificial milks that contained 15% total solids, and the energy intakes of groups of lambs within each dietary treatment varied from below maintenance to ad lib.Metabolizable energy (ME) as a percentage of the gross energy was constant for all diets, at all levels of energy intake, at 94·3 ± 0·3%. ME intake was linearly related to energy retention above maintenance with all diets. There was a significant linear decrease in the net efficiency of ME utilization as the protein content of the diet increased. However, the individual regressions did not differ significantly from the common regression coefficient of 0·686 ± 0·018, i.e. a net efficiency of 68·6 ± 1·8%. The individual coefficients were 0·740, 0·679 and 0·634 for diets A, B and C respectively.The ME requirement for energy equilibrium (maintenance) of lambs given diet B (100·4± 11·7 kcal/kg0·73 day) was significantly lower than that of lambs given diet A (126·4 ± 14·3) or diet C (119·2 ± 15·6). The energy costs of fat and protein deposition, calculated by multiple regression analysis of the pooled data, were 11·1 kcal ME per g fat and 8·5 kcal ME per g protein respectively.