Interactions among the branched-chain amino acids and their effects on methionine utilization in growing pigs: effects on nitrogen retention and amino acid utilization

An experiment was conducted to investigate the effects of branched-chain am ino acid (BCAA) interactions on their utilization by growing pigs and the e ffects of excessive amounts of BCAA (leucine, isoleucine, valine) on the ut ilization of methionine. A semipurified diet containing 100 g crude protein /kg with a balanced amino acid pattern was prepared using casein supplement ed with free amino acids. Three further diets were made by reducing the con centration of methionine +cyst(e)ine, valine or isoleucine by 20 %. Each of these four diets was then supplemented with leucine (50 % excess) or a mix ture of BCAA (50 % excess of each but excluding the limiting amino acid). A ll diets were isoenergetic and were made isonitrogenous by replacement of g lutamic and aspartic acids. The twelve diets were given to twenty-four grow ing pigs (30-40 kg) in three periods according to a randomized block design . Each period lasted 8d and N retention was measured during the last 5d of each period. Reducing dietary methionine, valine or isoleucine reduced the utilization of N (N retained/N digested) by approximately 20% (P < 0.05). A dding leucine to the isoleucine-limiting diet decreased the utilization of N by 9 % (P < 0.05). This was reversed by simultaneous addition of valine. Excess leucine in a valine-deficient diet did not significantly reduce N ut ilization. In methionine-limiting diets an excess of either leucine alone o r of all three BCAA increased the utilization of N by 8 % (P < 0.05).