Effects of different rumen undegradable to rumen degradable protein ratios on performance, ruminal fermentation, urinary purine derivatives, and carcass characteristics of growing lambs fed a high wheat straw-based diet

Abstract The present study aimed to evaluate the effects of various rumen undegradable to rumen degradable protein ratios (RUP:RDP) on the performance, rumen fermentation pattern, urinary purine derivatives, and carcass characteristics in growing lambs when received a high dietary wheat straw level (420 g/kg, DM basis). Lambs (average initial live weight = 27.2 ± 2.4 kg) were individual housed (n = 18, 6 animals/treatment) to evaluate the effects of treatments. The RUP:RDP ratios tested were obtained through replacing extruded soybean meal (ESBM; RUP = 64 %, based on total CP) instead of conventional soybean meal (CSBM; RUP = 26 %, based on total CP) in proportion of 0, 50, and 100 % in order to obtain ratios of (1) low RUP:RDP ratio as LR diet (25:75); (2) moderate RUP:RDP ratio as MR diet (30:70) (3) high RUP:RDP ratio as HR diet (35:65). The study lasted 10 weeks. Dry matter intake did not differ among experimental treatments (P = 0.80), while average daily gain (ADG) and final BW were linearly improved (P