Effect of different arginine-to-lysine ratios and guanidinoacetic acid supplementation on the growth performance, carcass characteristics and breast myopathies in broiler chickens

The aim of the study was to evaluate the effect of increasing the digestible arginine-to-lysine ratio (dig Arg:Lys) (Experiment 1), and to evaluate the Arg sparing effect of guanidinoacetic acid (GAA) (Experiment 2) on growth performance, carcass composition and breast myopathies in broiler chickens. In experiment (Exp) 1, a total of 672 male Ross 308 birds were assigned to 4 experimental groups provided in a 4-phase feeding scheme. The Control treatment had a dig Arg to Lys ratio (Arg:Lys) of 1.06, 1.06, 1.07 and 1.08 in starter, grower I, grower II and finisher diets, respectively; the other three experimental treatments had a dig Arg:Lys ratio of 1.15, 1.25 and 1.35 across all feeding phases by adding L-Arg to Control diets. In Exp 2, 504 male Ross 308 birds were fed using the same feeding scheme and assigned to 3 experimental groups: the Control diet had a dig Arg:Lys ratio of 1.05, and the other two treatments were supplemented with 0.6 g/kg GAA using two different dig Arg equivalency: 77% (GAA77) or 149% (GAA149). In Exp 1, body weight (BW), BW gain (BWG) and feed conversion ratio (FCR) were affected in a quadratic fashion (P ≤ 0.03 for all) at cumulative phases 0-10 and 0-20 d when increasing the dig Arg:Lys ratio. In these phases, the highest BW, BWG and best FCR were obtained with the highest dig Arg:Lys ratio (1.35). The latter effects were not observed for the phases 0-30 and 0-44 d. In Exp 2, the replacement of Arg by GAA did not affect the productive performance (P > 0.13) in the phases 0-20, 0-30 and 0-44 d, but GAA77 impaired FCR compared to control (P = 0.05) in phase 0-10 d. For carcass traits, only breast yield was increased in both GAA groups compared to Control (P = 0.01) at 35 d, and breast meat redness (a*) was decreased (P = 0.01) with GAA77 compared to CON. Skin scratches, breast myopathies, litter score and foot pad dermatitis were not affected by dietary treatments in any of the 2 Exps. In conclusion, increasing the dig Arg:Lys ratio to 1.35 has a positive effect on growth performance from 0-20 d of age without affecting breast myopathies incidence. Dietary supplementation of GAA could replace 77% of Arg without affecting performance parameters in broilers.