This investigation was carried out to determine body composition of protein, fat, and energy as well as nutritional requirements of protein and energy for maintenance and weight gain of Morada Nova Lambs. Thirty lambs averaging 15 kg of initial body weight (BW) were used in this trial. To determine the body composition using the comparative slaughter approach six lambs were slaughtered at 15 kg (reference animals), six at 20 kg (intermediary slaughter), and the remaining were distributed in one of six groups of three animals (one animal per diet) receiving the following forage (F):concentrate(C) ratios: 1) 40F:60C; 2) 55F:45C, and 3) 70F:30C. Lambs in each group were slaughtered when the animal fed the highest amount of concentrate reached 25 kg of BW. Body composition varied from 181.53 to 178.74 g of protein, 72.37 to 131.11 g of fat, and 1.81 to 2.34 Mcal of energy per kg of empty body weight (EBW). The net requirements of gain varied from 222.30 to 218.6 g of protein and from 3.30 to 4.28 Mcal of energy per kg of gained BW. The endogenous losses of nitrogen were of 0.332 g/kg0.75/day. The net requirement of energy for maintenance, estimated by heat production in fasted animals, was of 52.49 Kcal/kg0.75 of EBW. The requirements of metabolizable protein and energy for lambs from 15 to 25 kg of BW with daily weight gain of 100 g varied from 53.46 to 60.19 g/day and from 1.47 a 2.00 Mcal/day, respectively.
endogenous losses; gain requirements; heat production; maintenance; nitrogen; sheep
