Increasing standardized ileal digestible arginine-to-lysine ratios improves growth performance and carcass characteristics in 10- to 31-d-old broilers.

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.