Catabolism and Deposition of Amino Acids in Growing Chicks: Effect of Dietary Supply

Amino acid (AA) deposition and catabolism were examined in broilers by determining intake and carcass deposition of AA, while defining catabolism as the difference between intake and deposition. The first trial examined the effects of increasing concentrations of a single limiting AA, lysine, on carcass deposition and catabolism. Carcass deposition of all AA increased to a plateau. Catabolism of lysine increased linearly, whereas other AA showed decreased catabolism as dietary lysine increased before reaching a plateau. Carcass AA composition was not influenced by the diet. In the second trial, different dietary ratios of AA were examined and these resulted in increased carcass deposition of lysine, threonine, and arginine before reaching a plateau, whereas other AA showed constant deposition. Catabolism of all AA tended to increase with dietary concentration. Efficiency of AA deposition decreased with age and catabolism comprised a smaller proportion of intake in the first week posthatch. A third trial examined changing AA ratios and composition. No correlation was observed between dietary AA concentrations and carcass deposition, whereas catabolism was linearly correlated with dietary composition. Multiple regression analysis indicated that the catabolic pathways of some AA are interrelated. These data are consistent with a model where carcass accretion is determined by the limiting AA until some maximal rate is achieved, whereby another AA may become limiting. Excess supply of any AA is catabolized and these catabolic processes interact with an accompanying energy cost.