Muscle protein degradation assessed by N t -methylhistidine excretion in mature White Leghorn, dwarf broiler and normal broiler males maintained on either low- or high-protein diets

Abstract

Protein degradation rates were assessed by the excretion of N t -methylhistidine (N t MH) in four strains of mature chickens, two White Leghorns and two broilers (dwarf and normal), fed on diets containing two levels of dietary protein. Over 0.9 of labelled N t MH was recovered within 7 d of injection from three White Leghorn, three dwarf and three normal broiler males. Protein degradation, measured by N t MH output, was related to adult body-weight by the power 0.71 and strain intercepts were significantly different. Strain differences disappeared when the rate of output of N t MH per unit lean was evaluated. The rate of output of N t MH per unit muscle was higher in birds fed on a low-protein diet of 100 g crude protein (nitrogen x 6.25; CP)/kg compared with males fed on 150 g CP/kg. It was concluded that the lower rate of protein degradation in broiler compared with layer strains at young ages is related to increased adult body-weight in agreement with well-established biological principles.