A Congenital Progressive Ovine Muscular Dystrophy

Abstract

A congenital progressive myopathy affecting 2% of a flock of Merino sheep involved most of the muscles of the pelvic and pectoral girdles. The vastus intermedius muscle was consistently affected; at 2 years of age 50% of its fibers were replaced by fat and at 5 years almost all. Lesions were bilaterally symmetrical. Usually all components of the quadriceps muscle were involved, but scattered affected fibers were found in most other appendicular muscles. The lesions in the quadriceps muscles resulted in inability to flex the femoro-tibial joint, with consequent difficulty in locomotion, which, under range conditions, resulted in death from inability to forage. Histologically, affected muscles had rounded fibers with central and peripheral sarcoplasmic masses. The fibers contained vesicular nuclei that usually formed rows of up to 15, but occasionally up to 50. In 6-week-old lambs, muscle fibers ranged in diameter from 15-100 μ. No lesion was detected in the peripheral or central nervous system.