Ideal Amino Acid Profile for 28-to-34-Week-Old Laying Hens
The ideal amino acid (AA) profile employs the concept that, whereas absolute AA requirements change due to genetic or environmental factors, the ratios among them are only slightly affected. Thus, once the ideal AA profile has been determined, the requirement for a single AA (i.e., lysine) can be determined experimentally for a given field situation and the requirements for all the other AA calculated from the ideal ratios. Seven separate experiments were conducted with laying hens to determine the ideal ratio of arginine, isoleucine, methionine, methionine+cystine, threonine, tryptophan, and valine relative to lysine for maximal egg mass. The assays were conducted simultaneously using the same basal diet to which crystalline AA were added to create the graded level of the respective assay AA and to ensure that the assayed AA was first limiting. Hens were fed the assay diets from 26 to 34 weeks of age, with the first 2 weeks considered a depletion period. Egg production was recorded daily and egg weight was determined weekly on eggs collected over 48 hours; egg mass was calculated as egg production × egg weight. The requirement for each AA was determined using the broken-line regression method. Consumption of arginine did not affect egg mass, thus an ideal arginine:lysine ratio could not be determined. The ideal AA ratio for maximum egg mass for 28-to-34-week-old laying hens was isoleucine 79%, methionine 47%, methionine+cystine 94%, threonine 77%, tryptophan 22%, and valine 93% on a true digestible basis relative to lysine.