Increasing standardized ileal digestible arginine-to-lysine ratios improves growth performance and carcass...

This experiment was conducted to estimate the standardized ileal digestible (SID) arginine (Arg) to lysine (Lys) ratio requirements for broilers from 10 to 31 days of age. A total of 375 Ross 308 male broilers were assigned to 5 dietary treatments with 5 replicates of 15 birds using a randomized complete block design. Experimental diets set the SID Arg:Lys ratio of 85%, 95%, 105%, 115%, and 125%. Data were analyzed using the MIXED procedure, and Arg requirements were estimated using the NLIN procedure of SAS. During 10 to 21 days, a quadratic response in body weight gain (BWG) (P = 0.003) and a linear increase in gain-to-feed ratio (G:F) (P < 0.001) with increasing dietary SID Arg levels were observed. During 21 to 31 days, dietary SID Arg levels yielded a linear increase in BWG (P = 0.010) and a quadratic response for G:F (P = 0.026). Across 10 to 31 days, a quadratic response to dietary SID Arg levels was observed in BWG (P = 0.018) and G:F (P = 0.006). The dietary SID Arg levels increased linearly carcass yield (P = 0.005) and yielded quadratic responses for carcass weight (P = 0.029), breast meat weight (P = 0.003), and breast meat yield (P = 0.031). Estimated SID Arg:Lys ratio requirements, based on linear broken-line (LBL) and quadratic broken-line (QBL) models, ranged from 105.6% to 116.4% for BWG and 108.1% to 123.4% for G:F across the experimental periods. The LBL and QBL models were not significant for carcass yield. Dietary SID Arg levels linearly increased blood urea nitrogen (BUN; P = 0.027) and decreased mRNA expression of arginosuccinate synthase in liver (P = 0.025). In conclusion, the increasing dietary SID Arg:Lys ratio improved growth performance, carcass yield, and altered Arg metabolism in broilers. The optimal SID Arg:Lys requirements varied with response criteria used for estimation.