Maintenance and growth requirements in male and female hair lambs

Abstract

An experiment was conducted to evaluate the energy and protein requirements of intact male, castrated male and female Morada Nova lambs. The animals were distributed in a completely randomized 3×3 factorial design with three sexes (15 intact males, 16 castrated males and 16 females) and three levels of dietary restriction (ad libitum, 30% and 60% feed restriction) with an initial body weight (BW) of 14.50±0.89kg. Four animals per sex were slaughtered at the start of the trial as a baseline group. When the mean BW in the ad libitum treatment reached 28kg, at day 120 of the experiment, all lambs were slaughtered. For all sexes, the net energy requirement for maintenance was 73.0kcal/kg0.75 empty body weight (EBW)/d (P=0.17). The metabolizable energy efficiency for maintenance (km) was 0.58. The metabolizable energy efficiency utilization for gain (kg) was 0.36; 0.25 and 0.28 for intact males, castrated males and females, respectively. The net energy requirement for gain (NEg) differed (P<0.01) between sexes. The NEg was 0.191, 0.198 and 0.276Mcal/kg0.75 EBW/d for intact males, castrated males and females, respectively, with a BW of 20kg and a body weight gain (BWG) of 100g. The net and metabolizable protein requirements for maintenance obtained for lambs were 1.06g/kg0.75 BW/d (P=0.78) and 3.46g/kg0.75 BW/d (P=0.39), respectively. The net protein for gain (NPg) differed (P<0.01) between sexes. For animals weighing 20kg and with an average daily gain of 100g/d, NPg was 7.08, 7.11 and 6.78g/d for intact males, castrated males and females, respectively. The net energy and protein requirements for maintenance of Morada Nova lambs slaughtered between 15 and 28kg did not vary by sex. The net energy for gain increases and the net protein for gain decreased with the increase in body weight in hair lambs.