Influence of bone growth on muscle growth and bone-muscle relationships in double-muscled and normal cattle

Eighteen bulls each of double-muscled (DM), Beef Synthetic (SY) and Hereford (HE) breed types, serially slaughtered from about 250 to 800 kg live weight, were used to examine muscle-bone relationships in double-muscled and normal cattle.Relative to total side bone, DM animals differed significantly from the other breed types in relative growth rate of muscles in all regions which exhibited gross muscular hypertrophy. They showed generalized and regionally differentiated muscular hypertrophy. At equal bone weight in the given anatomical region, DM/HE and DM/SY muscle:bone ratios were respectively: proximal hindlimb 1·35 and 1·24; proximal forelimb 1·25 and 117; back and loin 1·20 and 1·10; and the expensive regions 1·30 and 1·20. In the limbs of DM animals, muscular hypertrophy in the proximal region was associated with bone hypotrophy while minimal muscular hypertrophy in the distal parts was associated with relatively heavier bones. Consequently, increased muscle:bone ratios were most pronounced in the proximal region, which suggests that muscles in these animals had increased in weight without proportionate increase of bones, i.e. muscle and bone growth were to some extent independent. Bone response in the distal limbs may have been influenced by a relative increase in weight support function.