The effect of morphology on the musculoskeletal system of the modern broiler
This study compares various morphometric features of two strains of broilers, selected and 'relaxed' (ie random-bred), raised under two feeding regimes, ad-libitum-fed and restrictedfed. We consider the possible consequences of the different body shapes on the musculoskeletal
system. The ad-libitum-fed selected birds reached heavier bodyweights at younger ages, had wider girths, and developed large amounts of breast muscle which probably displaced their centre of gravity cranially. At cull weight, they had shorter legs than birds in the other groups and
greater thigh-muscle masses; therefore, greater forces would have to be exerted by shorter lever arms in order to move the body. The tarsometatarsi were broader, providing increased resistance to greater loads, but the bones had a lower calcium and phosphorus content, which would theoretically
make them weaker. Many of these morphological changes are likely to have detrimental effects on the musculoskeletal system and therefore compromise the walking ability and welfare of the birds.