Abstract
We developed an experimental model of nutritional degenerative myopathy in ruminant cattle. Fourteen experimental calves were fed a diet low in vitamin E and selenium for 127 to 137 days. Six of these calves were then euthanatized. After 127 days, a dietary additive of linseed oil that had been treated to protect it against ruminal hydrogenation was added to the low vitamin E and selenium diet of the eight remaining calves as a source of polyunsaturated fatty acids. Six of these animals were euthanatized after 6 to 11 days of polyunsaturated fatty acid feeding; the other two died after 6 and 8 days. Macroscopic myocardial alterations were seen in five polyunsaturated fatty acid-fed calves but not in any other experimental calf. Microscopic lesions, comprising multifocal or diffuse cardiocyte degeneration and necrosis, were seen in atrial and ventricular myocardium of all experimental calves. These changes were more severe in polyunsaturated fatty acid-fed calves than in animals that did not receive polyunsaturates. Ultrastructurally, sublethally damaged cardiocytes had lysed contractile material; vacuolated sarcoplasm; altered mitochondria, sarcoplasmic myelin figures, and lipofuscin granules; and multiple nuclei. Necrotic cardiocytes had contracted myofibrils, pyknotic nuclei, mineralized mitochondria, and plasmalemmal disruption; the external lamina remained largely intact. Necrosis was followed by macrophage invasion and phagocytosis of necrotic debris. Repair of the lesions was by deposition of collagen and elastin fibers. No alterations were seen in the hearts of control calves fed vitamin E and selenium-supplemented diet. The induced myocardial lesions are similar to those of spontaneous nutritional degenerative myopathy in ruminant cattle.