True Amino Acid Digestibility Values Research Articles

Microbial phytase improves amino acid utilization in young chicks fed diets based on soybean meal but not diets based on peanut meal

Studies were conducted to evaluate the ability of supplemental microbial phytase to improve performance of young chicks fed phytate-containing, amino acid-deficient diets. Diets based on corn and peanut meal or soybean meal (SBM) and dextrose were fed to young chicks housed in battery cages for 10- and 13-d experimental periods. Assays were designed to evaluate phytase supplementation of both amino acid-deficient and amino acid-adequate diets. Weight gain, feed intake, and gain:feed values of chicks increased (P < 0.05) when deficient amino acids were serially supplemented to either the corn-peanut meal or SBM-dextrose diets. Phytase supplementation (600 and 1,200 U/kg) to the corn-peanut meal diet resulted in no significant differences in weight gain, feed intake, or gain:feed values of chicks when the diet was either deficient or adequate in amino acids. However, phytase supplementation (1,200 U/kg) produced significant increases (P < 0.05) in gain:feed values, but not weight gain, of chicks when they were fed the amino acid-deficient, but not the amino acid-adequate, SBM-dextrose diet. This gain:feed response to phytase supplementation of the amino acid-deficient SBM-dextrose diet occurred in both crossbred (New Hampshire x Columbian) and commercial (Ross x Hubbard) chicks. A digestibility assay was also performed using cecectomized roosters fed dehulled SBM containing three levels of phytase (0, 600, and 1,200 U/kg). When averaged across nine essential amino acids and cystine, true amino acid digestibility (TAAD) values were increased by approximately 2% when 1,200 U/kg phytase was included with SBM and administered to cecectomized roosters. However, neither TAAD values nor TMEn were significantly improved by the phytase addition.

Condensed Tannins Are Only Partially Responsible for Variations in Nutrient Digestibilities of Sorghum Grain Cultivars

Nitrogen-corrected true metabolizable energy (TMEn) and true amino acid digestibility values were determined, using cecectomized cockerels, for 20 sorghum [Sorghum bicolor (L.) Moench] cultivars that ranged in catechin equivalent (CE) percentages from 0 to 3.88. There were significant (P ≤ 0.01) overall inverse relationships between CE content and (1) the individual digestibilities of lysine, methionine, threonine, isoleucine, leucine, valine, phenylalanine, histidine, and arginine; (2) the mean digestibility of essential amino acids; (3) the mean digestibility of nonessential amino acids; and (4) TMEn values. In contrast to these overall trends, several cultivars of similar condensed tannin content had markedly different nutrient digestibilities. The dissimilarity of protein digestibilities in sorghum genotypes of similar tannin content was confirmed by subjecting samples of the ground grains to in vitro pepsin digestion with subsequent visualization of the undigested proteins by SDS−PAGE. The present wo...