Abstract
Skeletal muscle weight and muscle fiber characteristics of local meat-type Amakusa Daio chickens under single cage or flock floor rearing systems were examined in comparison with broilers. In broilers, body weight after skinning and weights of M. pectoralis and M. iliotibialis lateralis pars postacetabularis tended to be higher with flock floor rearing than with single cage rearing at 60 and 90 days old(P<0.1), with distinct differences between rearing types at 90 days old(P<0.05). On the other hand, Amakusa Daio chickens reared on the floor tend to show higher M. pectoralis weight than those with single cage rearing at 60, 90 and 120 days old(P<0.1), with particularly marked differences between rearing types at 90 days old(P<0.05). However, body weight after skinning and M. iliotibialis lateralis pars postacetabularis weights showed no significant differences between rearing types in Amakusa Daio chickens. In both chickens, M. pectoralis weight per 100 g body weight after skinning was shown to be somewhat higher with flock floor rearing than with single cage rearing (P<0.1). In particular, Amakusa Daio chickens revealed marked differences between rearing types at 60 and 90 days old(P<0.05). However, weights of M. iliotibialis lateralis pars postacetabularis in both chickens did not differ significantly between rearing types at 60, 90 or 120 days old. Broilers showed a marked increase in weight of the testes from 60 to 90 days old(P<0.01), as did Amakusa Daio chickens from 90 to 120 days old(P<0.01). Size of type IIR or type IIW myofibers in M. pectoralis of flock floor reared broilers tended to be larger than that of single cage reared chickens(P<0.1). In contrast, the number of type IIR myofibers from M. pectoralis and M. iliotibialis lateralis pars postacetabularis in flock floor reared Amakusa Daio chickens tend to increase from 60 to 90 days old(P<0.1). M. pectoralis and M. iliotibialis lateralis pars postacetabularis of flock floor reared Amakusa Daio chickens at 90 and 120 days old, compared to single cage reared chickens, showed a greater increase in the number of type IIR myofibers(P<0.05). M. pectoralis of flock floor reared Amakusa Daio chickens at 90 and 120 days old also showed a larger type IIR myofibers, compared to single cage reared chickens(P<0.05). These findings suggest that although flock floor rearing promotes better growth of skeletal muscle in both Amakusa Daio chickens and broilers, M. iliotibialis lateralis pars postacetabularis only shows better growth with marked development of the testes in later fattening, regardless of rearing type. Furthermore, effects of rearing type on muscle fiber characteristics were stronger in Amakusa Daio chickens than in broilers, and flock floor rearing increased the number of type IIR myofibers with age in local meat-type Amakusa Daio chickens.
