Ultrastructural changes in hereditary muscular hypertrophy in cattle.

Biopsies of skeletal muscle collected from 24 animals classified as “double muscled” were examined by light and electron microscopy. The muscle samples exhibited degenerative changes including the presence of vacuolations and lamellated structures, fragmentation of myofibers, accumulation of glycogen granules, disruption of neuromuscular junctions and disorganization of the sarcolemma. In the light of the excessive fragility of the erythrocyte membranes noted previously, the alteration in the sarcolemma suggests that a generalized cell membrane defect may be the most consistent feature of the “double muscling syndrome” in cattle.