Dietary guanidino acetic acid is an efficacious replacement for arginine for young chicks

Guanidino acetic acid (GAA) is synth-sized in the liver and kidney from Arg and Gly and subsequently methylated by S-adenosylmethionine to form creatine. Four bioassays were carried out to determine the capacity of GAA to serve as a dietary replacement for Arg for growing chicks. Broiler chicks were fed Arg-deficient dextrose-casein (0. 88% Arg) or corn-corn coproduct-soybean meal (1. 0% Arg) basal diets during 9-d battery feeding trials involving 5 pens of 4 chicks per treatment. The dextrose-casein diet was shown to be markedly deficient in Arg as both weight gain and G:F increased (P < 0. 01) due to addition of Arg, GAA, or creatine. The optimal level of added GAA was 0. 12% of the diet, but this level of GAA or 1. 0% creatine-H₂O did not improve growth performance when added to an Arg-adequate diet. A second assay confirmed this level of optimal Arg in a 2 × 2 factorial arrangement of l-Arg and GAA supplementation. Using a practical-type diet based on corn, corn gluten meal, distillers dried grains with solubles, and soybean meal, similar improvements (P < 0. 05) in G:F resulted from addition of 0. 25% Arg, 0. 12% GAA, or 0. 15% creatine·H₂O. These results demonstrate that 0. 12% supplemental GAA, like creatine, produces consistent growth responses in young chicks fed Arg-deficient diets. To provide further evidence of the capacity for GAA to serve as a dietary Arg replacement, the dextrose-casein diet was supplemented with 7 graded doses of Arg in the absence or presence of 0. 12% GAA (14 total diets). Quadratic (P < 0. 01) responses in weight gain and G:F responses to supplemental Arg were observed. Similar supplemental Arg requirements were estimated in the absence and presence of 0. 12% GAA, but GAA elicited a greater improvement (P < 0. 05) in G:F when added to Arg-deficient, compared with Arg-adequate, diets. Collectively, these data indicate that GAA can be used as an efficacious replacement for dietary Arg for young chicks.