Determination of the arginine, tryptophan, and glycine ideal-protein ratios in high-yield broiler chicks

In formulation, essential or semiessential and potentially limiting amino acids, such as Arg, Trp, and Gly, can sometimes be ignored and no minimum nutrient value assigned to these. Further, data estimating their dietary needs relative to dietary Lys are sparse and, in some cases, need formal revalidation. For that purpose, these 3 amino acids (Arg, Trp, Gly) were studied individually using Ross x Ross 708 chicks reared in a sex-separate manner and given progressive amounts of either Arg, Trp, or Gly relative to Lys. Birds were fed the diets from 0 to 18 d posthatch, and their BW and feed consumption were measured at 18 d of age. A blood sample was taken from birds from each experimental unit during all 3 studies and analyzed for certain blood plasma metabolites to further evaluate the nutritional status of these chicks. Sex did not interact with diet for any of the amino acids studied, so regression analysis was performed using all the experimental units averaged across sexes, thus resembling straight-run flocks. The Arg: Lys ratio was found to be optimized between 106 and 114%, depending on the response parameter. Furthermore, livability was seriously compromised with lower Arg: Lys treatments, but any deleterious effect was dissipated when a minimum of 103% of dietary Arg: Lys was fed to the chicks. Dietary Trp was found to be adequate between 17 and 19% of dietary Lys, whereas (Gly + Ser): Lys was calculated to be adequate at a ratio of 161% for BW gain. Feed conversion was observed to improve linearly up to the highest level of (Gly + Ser): Lys fed. Therefore, Gly + Ser needs may be elevated because of the possible inefficient biosynthesis of Gly by the chick, and this should be the focus of future research.