Growth and in vitro protein synthesis in two strains of chicks.

An in vitro method was used to estimate rates of skeletal muscle protein synthesis and degradation in fast (broiler) and slow (White Leghorn) growing birds. Four birds/strain were sacrificed at weekly intervals for 8 wk and biweekly thereafter to wk 14. The extensor digitalis communis, a muscle containing both red and white type fibers and the extensor carpi ulnaris, a white fiber-type muscle, were removed from the right wing and incubated in a Krebs-Ringer solution that contained either 14C-tyrosine for determination of rates of protein synthesis or cycloheximide for determination of rates of protein degradation. The contralateral muscles were removed and muscle weight, length and volume recorded. Proximate analysis was conducted on the carcass and inedible portions of the birds to determine protein, fat and moisture content. Nucleic acid concentrations were measured in the wing muscles. Broilers grew more rapidly than Leghorns, with a twofold difference in body weight by wk 3 and a threefold difference by wk 8. The greater total protein deposition, with more of this protein deposited in the carcass portion than the inedible portion. White muscle had a greater growth rate than the mixed fiber type muscle. Concentrations of RNA and DNA were similar between strains.