Comparison of muscle growth between meat-type and egg-type chickens

Muscle growth of White Leghorn and White Cornish was compared by determining fiber diameter and number, deoxyribonucleic acid (DNA) content per muscle and the ratio of nitrogen to DNA (N/DNA ratio) in M. pectoralis superficialis, M. pectoralis profundus, M. sartorius and M. gastrocnemius removed from chicks aged 0, 2 and 8 weeks. 1. No breed difference existed in fiber diameter of muscles tested, except for M. pectoralis profundus of day-old chicks and M. sartorius of 2-and 8-week-old chicks. Each muscle of White Cornish had significantly more fiber number than that of White Leghorn. 2. No significant difference existed in DNA content per muscle between day-old chicks of both breeds, but DNA content in White Cornish increased more rapidly after hatching than that in White Leghorn. No breed difference existed in N/DNA ratio in muscle of chicks aged 0 and 2 weeks. At 8 weeks of age, the ratio in leg muscles of White Leghorn was slightly higher than that of White Cornish. 3. A significant correlation existed between muscle weight and fiber number and between muscle weight and DNA content per muscle, but correlations between muscle weight and fiber diameter and between muscle weight and N/DNA ratio were not significant.