Muscle growth in light and heavy types of chickens

The absolute and relative growth of leg muscle (M. gastrocnemius), breast m uscle (M. pectorialis superficialis) and wing muscle (M. biceps brachii) in male light (Issa Brown) and heavy (Ross-1) types of chickens was estimated at one week intervals, from hatching to eight weeks of age. On the first day after hatching there were no significant differences in mu scle weight between the two strains. After that, the weight of all muscles was significantly (p<0.01) greater in heavy type chickens. The relative gro wth of muscles, in both strains, showed a rapid increase during the first d ay of age, and after that decreased. Growth rate of muscles was greater in heavy type chickens during the first two-three weeks of age. During this pe riod the breast muscle grew faster than wing and leg muscles.