An experiment was carried to evaluate the energy and protein requirements for the growth and maintenance of lambs of different sex classes. In all, 38 hair lambs (13.0±1.49 kg initial BW and 2 months old) were allocated in a factorial design with diet restriction levels (ad libitum, 30% and 60% feed restriction) and sex classes (castrated and non-castrated males). Four animals from each sex class were slaughtered at the beginning of the trial as a reference group to estimate the initial empty BW and body composition. The remaining lambs were weighed weekly to calculate BW gain (BWG), and when the animals fed ad libitum reached an average BW of 30 kg, all of the experimental animals were slaughtered. Before slaughter, fasted BW (FBW) was determined after 18 h without feed and water. Feed restriction induced reductions in body fat and energy concentration, whereas water restriction showed the opposite effect, and the protein concentration was not affected. The increase in BW promoted increases in body fat and energy content, and these increases were greater in castrated lambs, whereas the protein content was similar between classes tending to stabilize. The net energy required for gain (NEg) and the net protein required for gain (NPg) were not affected by sex class; therefore, an equation was generated for the combined results of both castrated and non-castrated lambs. The NEg varied from 1.13 to 2.01 MJ/day for lambs with BW of 15 and 30 kg and BWG of 200 g. The NPg varied from 24.57 to 16.33 g/day for lambs with BW of 15 and 30 kg and BWG of 200 g. The metabolizable energy efficiency for gain (k g) was 0.37, and the metabolizable protein efficiency for gain (k pg) was 0.28. The net energy required for maintenance (NEm) and the net requirement of protein for maintenance (NPm) did not differ between castrated and non-castrated lambs, with values of 0.241 MJ/kg FBW0.75 per day and 1.30 g/kg FBW0.75 per day, respectively. The metabolizable energy efficiency for maintenance (k m) was 0.60, and the efficiency of metabolizable protein use for maintenance (k pm) was 0.57. Nutritional requirements for growth and maintenance did not differ between castrated and non-castrated lambs. This study emphasizes the importance of updating the tables of international committees and of including data obtained from studies with sheep breeds raised in tropical conditions, with the purpose of improving the productive efficiency of the animals

An experiment was conducted to evaluate the effects of feed restriction (FR) and sex on the quantitative and qualitative carcass traits of Morada Nova lambs. Thirty-five animals with an initial body weight of 14.5 ± 0.89 kg and age of 120 d were used in a completely randomized study with a 3 × 3 factorial scheme consisting of three sexes (11 entire males, 12 castrated males and 12 females) and three levels of feeding (ad libitum – AL and 30% and 60% FR). Entire males presented greater hot and cold carcass weights (P < 0.05), followed by castrated males and females. However, the hot carcass yield was higher for females and castrated males than for entire males. Luminosity values were influenced (P < 0.05) by sex, with entire males presenting higher values than castrated males and females. Females showed higher (P < 0.05) concentrations of linoleic acid and arachidonic acid in the meat of the longissimus thoracis muscle. The meat of animals submitted to AL intake and 30% FR showed similar (P > 0.05) concentrations, and the concentrations of palmitic acid, palmitoleic acid, stearic acid, oleic acid and conjugated linoleic acid were higher (P < 0.05) than those of animals with 60% FR. The meat of females had a higher ω6/ω3 ratio and lower h/H ratio, and females had greater levels of feeding. The meat of animals on the 60% FR diet had a greater ω6/ω3 ratio, lower h/H ratio and lower concentration of desirable fatty acids in addition to a greater atherogenicity index (AI) and thrombogenicity index (TI). Lambs of different sexes had carcasses with different quantitative traits without total influence on the chemical and physical meat characteristics. The lipid profile of the meat was less favorable to consumer health when the animals were female or submitted to 60% feed restriction.