Net protein and energy requirements for weight gain of Santa Inês and Morada Nova sheep

The objective of this study was to determine the body composition and the dietary protein and energy requirements for weight gain of Santa Inês and Morada Nova sheep. A total of 48 intact lambs (24 Santa Inês and 24 Morada Nova), with initial weights of 21.7 ± 1.2 kg and 20.8 ± 0.8 kg and ages of 170 and 190 days, respectively, were used. At the beginning of the experimental phase, six lambs of each breed were slaughtered to determine body composition. The remaining 36 animals were divided into six groups of six animals each, separated by slaughter weights (25, 28 and 31 kg) and genotypes. The comparative slaughter technique was used to determine the nutritional requirements. The respective net requirements for energy gain ranged from 3.07 to 3.42 and 3.40 to 4.08 Mcal/kg gain of empty body weight (EBW), while for protein gain, the requirements ranged from 140 to 132 and 113 to 102 g/kg of EBW gain for intact genotypes lambs weighing between 22 and 31 kg. The Santa Inês sheep had higher net protein but lower net energy requirements for weight gain than the Morada Nova sheep. The body composition and the net requirements of protein and energy gains of genotypes sheep differ from the values reported by the main international committees of nutritional assessments.