Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2007
Publication Date: 3/15/2008
Citation: Bregendahl, K., Roberts, S.A., Kerr, B.J., Hoehler, D. 2008. Ideal ratios of isoleucine, methionine, methionine plus cystine, threonine, tryptophan, and valine relative to lysine for white leghorn-type laying hens of twenty-eight to thirty-four weeks of age. Poultry Science. 87:744-758. Interpretive Summary: Amino acid (AA) requirements currently recommended for laying hens are dated and do not account for the genetic progress of laying hens that has occurred over the last 15 yr. Recently published experiments have been conducted for a single AA at a time and were performed under different experimental conditions (i.e., different basal diets, genetic lines, feed consumption rates, dietary energy contents, feedstuffs, ambient temperature, cage space, and bird age, etc.) which in'uence AA requirements of the laying hen. In this experiment, the ideal AA concept was evaluated in that while absolute AA requirements change due to genetic or environmental factors, the ratios among them are only slightly affected. Data presented provided revised AA to lysine ratios allowing poultry nutritionists a basis from which to formulate diets to mimimize dietary crude protein (nitrogen) cost, improve the efficiency of crude protein (nitrogen) retention in the bird, and consequently reduct the excretion of nitrogen into the environment from egg laying facilities.
Technical Abstract: Seven separate experiments were conducted with Hy-Line W-36 hens to determine the ideal ratio of Arg, Ile, Met, Met+Cys, Thr, Trp, and Val relative to Lys for maximal egg mass. The experiments were conducted simultaneously and were each designed as a randomized complete block design with 60 experimental units (each consisting of 1 cage with 2 hens) and 5 dietary treatments. The 35 assay diets were made from a common basal diet (2,987 kcal/kg of ME; 12.3% CP; 4.06% Ca, 0.47% nonphytate P), formulated using corn, soybean meal, and meat and bone meal. The true digestible amino acid contents in the basal diet were determined using the precision-fed assay with adult cecectomized roosters. Crystalline L-Arg (free base), L-Ile, L-Lys-HCl, DL-Met, L-Thr, L-Trp, and L-Val (considered 100% true digestible) were added to the basal diet at the expense of cornstarch to make the respective assayed amino acid first limiting and to yield 5 graded inclusions of the assayed amino acid. 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 x egg weight. The requirement for each amino acid was determined using the broken-line regression method. Consumption of Arg did not affect egg mass, thus a requirement could not be determined. The true digestible amino acid requirements used to calculate the ideal amino acid ratio for maximum egg mass were 426 mg/d of Ile, 538 mg/d of Lys, 253 mg/d of Met, 506 mg/d of Met+Cys, 414 mg/d of Thr, 120 mg/d of Trp, and 501 mg/d of Val. The ideal amino acid ratio for maximum egg mass was Ile 79%, Met 47%, Met+Cys 94%, Thr 77%, Trp 22%, and Val 93% on a true digestible basis relative to Lys. The ideal Met and Met+Cys ratios were veri'ed in an ensuing identical experiment with 52 to 58-week old hens.