Determination of energy and protein requirement for maintenance and growth and evaluation for the effects of gender upon nutrient requirement in Dorper × Hu Crossbred Lambs

This study aimed to determine energy and protein requirement of Dorper × Hu crossbred lambs and further to evaluate the effect of gender upon nutrient requirement parameters. Forty-two female lambs (18.60 ± 1.57 kg) and 42 male lambs (18.30 ± 1.28 kg) were used. In comparative slaughter trial, 30 of animals from each gender group were randomly selected and assigned to ad libitum (AL), low restriction (LR) and high restriction (HR) group, and then were slaughtered when lambs under AL treatment reached target BW of 20, 28, and 35 kg, to determine body energy and nitrogen retained. In digestibility trial, remaining 12 female (18.01 ± 1.66 kg) and 12 male lambs (18.43 ± 1.17 kg) were randomly assigned to three feeding treatments in accordance with the design of comparative slaughter trial, to evaluate dietary energetic values at different feed intake levels. The combined data indicated that metabolizable energy (ME) requirement for maintenance (MEm; 400.61 ± 20.31 vs. 427.24 ± 18.70 kJ kg−1 of shrunk BW0.75; SBW0.75), partial efficiency of ME utilization for maintenance (km; 0.64 ± 0.02 vs. 0.65 ± 0.03), partial efficiency of ME utilization for growth (kg; 0.42 ± 0.03 vs. 0.44 ± 0.02), and net protein (NP) requirement for maintenance (NPm; 1.83 ± 0.17 vs. 1.99 ± 0.28 g kg−1 of SBW0.75) did not differ (P > 0.05) due to gender; although not statistically different, the mean value of Net energy (NE) requirement for maintenance (NEm) for male lambs (260.62 ± 13.21 kJ kg−1 of SBW0.75) were 5 % greater than that (274.16 ± 11.99 kJ kg−1 of SBW0.75) of female lambs. Additionally, rams have greater amounts of NP requirement for growth (NPg, 15.94 to 44.32 g d−1) than those of ewes (13.07 to 32.95 g d−1) at the similar condition of BW and ADG. In conclusion, we suggested that our results of energy and protein requirement for growth ranged between the NRC recommendation for early and later maturating growing sheep, and the effect of gender upon energy requirement parameters was similar in tendency but was less evidently than those frequently recommended previously.