CONGENITAL MYOPATHY IN BRAUNVIEH X BROWN SWISS CALVES

A hitherto unknown skeletal muscle disorder is described in six Braunv ieh x Brown Swiss calves. The animals showed rapidly progressing muscu lar weakness and became recumbent within 2 weeks of birth. Histologica l examination of skeletal muscle revealed a marked variation in muscle fibre size, internally placed nuclei, segmental loss of cross-striati on with disorganization of myofibrils, and accumulation of nemaline ro ds. The most distinctive histological finding was intracytoplasmic, ho mogeneous, mostly crescent-shaped areas at the periphery of numerous m uscle fibres. Electron microscopically, accumulations of tightly packe d, parallel filamentous structures: about 20 nm in diameter, were dete cted in these areas. Enzyme histochemistry showed that all muscle fibr e types were affected. Vimentin and dystrophin immunohistochemistry re vealed normal antigen distribution within connective tissue components and at the periphery of each muscle fibre, respectively. The lesions could be readily distinguished from other neurological and neuromuscul ar disorders previously described in Braunvieh x Brown Swiss or Americ an Brown Swiss cattle. The disease appears to be a novel congenital my opathy in this breed, and a hereditary aetiology is suspected. (C) 199 6 W.B. Saunders Company Limited