Amino acid requirements of growing pigs 2. Identification of the limiting amino acid(s) in a low-protein diet supplemented with lysine

Abstract

ABSTRACTA basal diet containing 120 g crude protein per kg and 9g lysine per kg, and previously shown to be limiting in one or more essential amino acids and/or non-essential nitrogen, was examined. It was fed either alone to growing female pigs from 25 kg to 55 kg live weight or in combination with four supplements of synthetic amino acids each containing three out of isoleucine, methionine, threonine and tryptophan. A control diet containing 140 g crude protein per kg and 9g lysine per kg was also included. Blood samples were collected at 40 kg live weight in order to examine the influence of dietary treatments on blood metabolites. Results for growth performance, carcass composition and blood urea indicated that threonine was the first limiting amino acid in the basal diet. Plasma free amino acids gave no clear trend. Growth performance and carcass composition were unaffected by supplementation of the diet with glycine indicating that the dietary supply of non-essential nitrogen was adequate.