Growth characteristics, protein synthesis, and protein degradation in muscles from fast and slow-growing chickens.

Developmental changes in muscle growth were studied in Single Comb White Leghorn (SCWL) and broiler-type (B) chickens. The extensor digiti communus (EDC) and ulnaris lateralis (UL) muscles were chosen for study because these muscles can be maintained in vitro, permitting the direct measurement of the fractional rate of protein synthesis (FSR) and the fractional rate of degradation (FDR). These muscles were removed from chicks at 1, 5, 10, and 20 days of age. Muscles for B were heavier, grew at a faster rate, and had greater fractional rates of growth than muscles from SCWL. Muscle protein concentrations were similar for SCWL and B. The deoxyribonucleic acid (DNA) concentrations were greater in EDC muscles from SCWL than B at all time periods. Concentrations of DNA were greater in UL muscles from SCWL than B after Day 1. The FSR and FDR were measured in muscles incubated in vitro. At 9 days of age, FSR in broiler and SCWL chicks was not significantly different in either muscle. The FDR was 12 and 19% lower in broiler EDC and UL muscles, respectively, demonstrating that broiler EDC and UL muscles accrete protein at a greater rate and more efficiently than SCWL muscles because of a slower rate of protein degradation. The FSR and FDR were also compared in B and SCWL chicks of 8 and 11 days, respectively, with equal DNA unit sizes. The FSR in B was 27 and 13% greater in EDC and UL muscles, respectively, demonstrating that protein synthesis per nucleus is greater in B chicks.