Body composition and net protein and energy requirements of four genetic groups of lambs

This study was carried out at the Sheep Sector of the Animal Production Department of the Federal University of Lavras, Minas Gerais. The protein, fat and energy body content was evaluated and the net requirements of protein and energy for weight gain of lambs were determined. Forty-eight uncastrated male lambs, pure Santa Ines (SI) and crossed Texel x Santa Ines (TxSI), Ile de France x Santa Ines (IFxSI) and Bergamacia x Santa Ines (BxSI), maintained in feedlot and slaughtered to the 15, 25, 35 and 45 kg of live weight, were used. Regression analyses of the logarithm of protein, fat and energy body content in function of the empty body weight (EBW) logarithm were fitted. The net requirements of protein and energy for weight gain were obtained by derivation of the prediction equations of body composition. A test of comparison of the coefficients of regression of the obtained logarithmic equations was accomplished, which detected differences among the lambs TxSI and the others. The protein body content decreased but fat and energy body content increased in according to the EBW increase, for all genetic groups. The TxSI lambs presented larger net protein and energy requirements for live weight gain than SI, IFxSI and BxSI lambs.