Comparative energy and protein utilization in kids and lambs

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Abstract
Twenty-eight male castrate kids and 28 male castrate lambs were assigned to a comparative slaughter experiment to compare energy and protein utilization. The experiment was conducted from January to March at Lincoln, New Zealand. Ten animals of each species comprised the initial slaughter group while the remaining 18 animals were randomly allocated to five feeding regimes. Animals were offered high-quality meadow hay for 13 weeks and then slaughtered. The energy retained in the body was regressed against metabolizable energy intake (MEI) to obtain estimates of maintenance energy requirement (MEm) and efficiency of energy utilization for growth (kg).Kids tended to have a higher MEm (0·44 v. 0·37 MJ ME/kg W0·75 per day in kids and lambs, respectively) and a higher kg (0·28v. 0·22) though these differences were not significant. There was no difference between the species in the composition of gain of the fleece or hair-free body with a protein energy to gross energy ratio in the gain of 0·20. The fleece or hair-free body composition was similar for both species (initial 0·51v. 0·48; final 0·36 v. 0·32; protein energy:gross energy, kids and lambs, respectively). Overall, the values for kg in both species were low and could not be explained solely by the composition of the gain.The efficiency of use of apparently absorbed amino acid (AA) for fleece or hair-free body protein deposition was higher for kids (0·52 v. 0·29) and, when the fleece or hair was included, the value increased markedly for lambs (0·50 v. 0·41, kids v. lambs, respectively). The protein energy apparently absorbed in the small intestine/MEI was not high or different between species (mean 0·18). The efficiency values for both species are low and not explained by the supply of protein relative to energy, which was not high.It was concluded that, with high-quality forage used to promote live weight gain, there was little difference between kids and lambs in the utilization of forage energy, and that the efficiency of utilization of absorbed protein for protein deposition was lower than expected in both species.