COMPARISON OF THE FETAL DEVELOPMENT OF MUSCLE IN NORMAL AND DOUBLE-MUSCLED CATTLE

Muscle differentiation was studied in foetal Semitendinosus muscle fro m normal cattle and those with the 'culard' gene of muscular hypertrop hy sampled at 90, 130, 170 and 210 days of foetal life. The different fibre types were characterized by immunohistochemistry with antibodies specific to different isoforms of myosin heavy chains. The isoforms w ere separated by electrophoresis, identified by immunoblotting and qua ntified by ELISA. In double-muscled animals, there was a slower rate o f differentiation in the first generation of cells, most markedly appa rent at 90 days. At 130 days, differentiation was retarded mainly in t he second generation, while at 170 days there was no longer any differ ence between the two animal types in the differentiation of first gene ration cells, which were totally slow in both. At the same stage howev er, type IIC fibres in double-muscled animals were much slower in appe aring and continued to be so at 210 days, albeit to a lesser extent. T hese findings show that differentiation of the muscle fibres occurs at a slower rate in double-muscled foetuses particularly during the firs t two-thirds of foetal life.