Birds fed with vegetable diets rely on the endogenous synthesis of creatine, which requires amino acids, some of which, for example arginine (Arg), are considered essential for several physiological and metabolic functions. Creatine is limited to high energy expenditure cells, particularly muscle cells. The objective of this study was to evaluate the inclusion of guanidinoacetic acid and arginine (as precursors of creatine) in vegetable diets, on the performance, quality, and yield of broiler chickens. The treatments consisted of diets based on corn and soybean meal (T1); corn, soybean meal + 3% meat meal (T2); corn, soybean meal + 0.08% guanidinoacetic acid (T3); and corn, soybean meal + 0.08% L-arginine (T4). The productive performance of the birds aged 7-, 21-, and 42-days-old was determined. Eighteen 7-day-old birds were sacrificed per treatment to evaluate breast and leg yield, and breast muscle fibers, and eighteen 42-day-old birds were sampled per treatment to determine serum uric acid, urea, creatine, lactate, and glucose concentrations. The same birds were slaughtered to calculate carcass yield in relation to live weight and commercial cut yield. The right pectoralis major muscle of each bird was used to test pH, color (luminosity L*, red index a*, and yellow index b*), and loss of water by pressure analysis, and the left side was used to analyze losses by defrosting and cooking. The data were analyzed using the software SAS. Diets to which meat or vegetable meal plus guanidinoacetic acid or L-Arginine were added resulted in higher live weight and breast meat percentage at 7 days old. Feed conversion was affected for a total period of 1 to 42 days of age (P < 0.0002). The birds with a diet supplemented with vegetable and meat meal had better feed conversion when compared to the birds that were fed with other diets. Treatments did not affect carcass and commercial cut yields, percent loss by cooking, pressure and defrosting of the broiler breast meat, or color (L, a*, and b*) and pH values. Key words: Weight gain. Glycine. ATP re-synthesis. ResumoAves alimentadas com dietas vegetais dependem da síntese endógena de creatina, que requer a participação de aminoácidos, alguns deles considerados essenciais para diversas funções fisiológicas e metabólicas, como a arginina (Arg). A creatina limita-se a células de alto gasto energético, em particular as células musculares. O objetivo foi avaliar a inclusão do ácido guanidinoacético e de arginina como precursor da creatina em dietas vegetais sobre o desempenho, a qualidade e o rendimento de carcaça de frangos de corte. Os tratamentos consistiram em dietas baseadas em milho e farelo de soja (T1); dieta a base de milho, farelo de soja + 3% de farinha de carne (T2); dieta a base de milho e farelo de soja +0,08% de ácido guanidinoacético (T3) e dieta a base de milho e farelo de soja +0,08% de L-arginina (T4). O desempenho produtivo das aves foi determinado aos 7, 21 e 42 dias de idade. Aos sete dias de idade, 18 aves/tratamento foram sacrificadas para avalia...

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