Carcass composition and skeletal muscle distribution in broilers produced under different nutritional regimes-1: Male chicks at three weeks of age

1. During early post-hatching growth in chickens, the wing muscles develop rapidly and their size relative to hind limb muscles increases (Iwamoto et al., 1975b; Ono et al., 1989). The aim of the present study was to assess whether the ratio of hind limb to wing muscle weight at three weeks of age could be altered by nutritional restriction during early growth. 2. Four groups of male chicks were reared on different complete feeds for three weeks. The feeds were: broiler finisher (BF; ME 13.47 MJ/kg, CP 180 g/kg), layer starter CLS; ME 12.34 MJ/kg, CP 210g/kg), layer grower (LG; ME 11.92 MJ/kg, CP 170 g/kg) and pre-layer (PL; ME 11.72 MJ/kg, CP 140 g/kg) feeds. 3. Growth rate differed among the chick groups; both live weights and carcass weights were highest in BF chicks, followed by LS, LG and PL chicks. There was a 2.4-fold difference in live weight and carcass weight between the BF and PL chicks. The weight of carcass as a percentage of live weight was 81-82% and did not differ among the chick groups. 4. The percentage of the carcass made up of skeletal muscle was positively associated with carcass weight while the percentage made up of viscera was negatively associated with carcass weight. However, the percentage of carcass weight accounted for by bone and skin did not differ among the chick groups. LG and PL chicks had higher proportions of intermuscular and abdominal fats than the other treatment groups. 5. The wing and hind limb muscles generally made up a higher percentage of the heavier carcasses. The weight of hind limb muscle relative to wing muscle in PL chicks was 96.7% while the equivalent value in the other groups was in the range 79.6-83.3%. Shoulder girdle muscle was the major component of wing muscle while the femoral and crural muscles accounted for a large proportion of the total hind limb muscle. 6. Our results suggest that severe restriction of body growth induced by under-nutrition increases the size of the hind limb muscle relative to wing muscle as a result of greater depression of muscle development in the wing than in the hind limb.