The objective of this study was to evaluate the supplementation of guanidinoacetic acid (GAA) and L-arginine (L-Arg) as creatine precursors to vegetable diets on the carcass yield and meat quality of broilers subjected to two days of heat stress before slaughter. A total of 1260 broiler chicks were distributed according to a completely randomized design into four treatments with nine replicates of 35 birds each. The treatments consisted of: T1 -vegetable diet based on corn and soybean meal (control diet); T2 -control diet with the inclusion of meat meal (3%); T3 -control diet supplemented with GAA (0.08%); and T4 -control diet supplemented with L-Arg (0.8%). The birds were submitted to heat stress for two days before slaughter (from 42 to 44 days of age). The birds fed the diets supplemented with GAA or L-Arg presented heavier carcasses (p<0.0035), higher breast yield (p=0.0685), and lower of abdominal fat deposition (p=0.0508) than those fed the control diet and the control diet with meat meal. The cooking loss of the breast fillets of broilers fed the control diet supplemented with meat meal, GAA or L-Arg was lower (p<0.0068) compared with those fed the control diet. Thawing and pressure-driven breast fillet weight losses, and pH, luminosity, redness (a*value), and yellowness (b* value) values were not influenced by the treatments. When GAA is less expensive than commercially-available Arg, the dietary supplementation of GAA is more advantageous, based on the meat yield improvements observed in the present study.

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