The effect of dietary protein levels on body weight gain, carcass production, nitrogen emission, and efficiency of productions related to emissions in thin-tailed lambs

Aim: This study was aimed to evaluate dietary crude protein (CP) level on performance of body weight (BW) gain, carcass production, and nitrogen emission on lambs. Materials and Methods: A total of 12 male thin-tailed lambs (15.2 +/- 1.8 kg initial BW and aged 3-4 months) were assigned to completely randomized design for 84-day feeding trial. The animals were divided into three different levels of CP (i.e., 14%, 16%, and 18% with isocaloric diets and 60% total digestible nutrients) with four replications. Results: Increasing CP level was not significantly affected on average daily gain (ADG), carcass production, N and N2O emissions, and efficiency of emissions related to the productions. The average of ADG, carcass production, meat production, meat protein production, N emission, and N2O emission was 141.4 g, 11.6 kg, 6.8 kg, 0.9 kg, 53.1 g/day, and 0.3g/day, respectively. The efficiency of ADG, carcass production, meat production, and meat protein related to N emissions were 119.7 g/kg, 4.4 g/kg, 2.5 g/kg, and 56.6 g/kg, respectively, while N2O emissions related to ADG, carcass production, meat production, and meat protein were 2.4 g/kg, 0.027 g/kg, 0.36 g/kg, and 0.34 g/kg, respectively. Conclusion: It can be concluded that the increase of CP level up to 18% did not affect productivity, N emissions, and efficiency of emissions per unit product because the increase of CP was not balanced by energy content in feed.