Effect of Dietary Lysine Level in a Wheat Protein Diet on Growth and Changes in DNA, RNA and Protein Composition in the Tissue of Broiler Chicks

Abstract

The impact of deficiency and excess dietary lysine on chick body and tissue cell growth was measured. Wheat protein diets (15%) supplemented with 0.25, 0.5, 0.75 and 1.0% l-lysine were fed to broiler chicks from one to 28 days of age. Gastrocnemius muscle and liver DNA, RNA and protein composition were measured at 14 and 28 days of age.Optimum chick growth was obtained with 0.86% dietary lysine (0.5% l-lysine supplemented to wheat protein). Muscle DNA (mg./g. wet tissue) was unaffected by the level of dietary lysine at 14 and 28 days of age. Liver DNA increased at 14 days and was unaffected at 28 days with increased level of dietary lysine. Muscle protein/DNA and RNA/DNA ratios increased at 14 and 28 days of age by supplementing wheat with lysine. The ratios decreased at dietary lysine levels higher than 0.86%. Liver protein/DNA and RNA/DNA ratios decreased progressively with increased dietary lysine at 14 days of age and increased in a manner similar to muscle at 28 days. Liver protein/RNA ratio at both 14 and 28 days was constant and independent of lysine intake indicating that RNA is correlated with protein biosynthesis. Results indicate that muscle growth in the chick is by an increase in cell size and not in cell number from hatch to 28 days of age whereas the liver undergoes rapid cell multiplication during the first 14 days and growth at 28 days is mostly by cell hypertrophy. The response of body growth in the chick was directly related to the amount of lysine available for tissue protein synthesis and liver cell multiplication from a dietary deficiency to the lysine requirement.