FACTORS AFFECTING THE DEVELOPMENT OF NUTRITIONAL MUSCULAR DYSTROPHY IN NORTHERN ONTARIO

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Abstract
Fall calves from beef cows fed dystrophy-producing hay were found susceptible to the development of muscular dystrophy at an early age when exposed to severe outwintering conditions. Histopathological examination revealed granular discoid and hyaline degeneration of skeletal muscles in all the dystrophic calves and in two of the animals, hyaline degeneration of the heart was observed. All the affected calves died before 14 days of age. No appreciable rise in serum glutamic oxalacetic transaminase values were found for dystrophic calves, evidently due to the extreme rapidity in which myopathy developed and subsequent death ensued.Spring calves from dams fed dystrophy-producing hay during the winter developed myopathy after their release to pasture. A markedly higher incidence of dystrophy occurred in calves which had been reared outside and allowed normal exercise in comparison to calves which had been confined indoors, suggesting that the pasture effect is not related to an increase in physical activity or alteration of climate.Electrocardiography was found to be a useful tool for diagnosis of the cardiac myopathy frequently observed in dystrophic calves. Electrocardiograms of affected calves showed widening of the QT interval, and non-isoelectric ST and whipped T-wave configurations.

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