CARDIOMYOPATHY OF RUMINANTS INDUCED BY THE LITTER OF POULTRY FED ON RATIONS CONTAINING THE IONOPHORE ANTIBIOTIC, MADURAMICIN .2. MACROPATHOLOGY AND HISTOPATHOLOGY

This report contains an account of the gross and histopathological les ions of 20 cattle and four sheep in 15 field outbreaks of poultry litt er toxicity, one steer fed ad lib. and six sheep dosed with toxic poul try litter, and ten sheep fed experimental rations containing c 2,5 pp m and 5 ppm maduramicin. The principle macroscopic lesions in most cat tle that died in field outbreaks were indicative of congestive heart f ailure. The lesions in sheep were similar, but generally milder. Cardi ac dilatation was observed in both sheep and cattle. Microscopically, the cardiac lesions were more pronounced in cattle and comprised varyi ng degrees of atrophy, hypertrophy, degeneration, necrosis of myocardi al fibres, and interstitial fibrosis. Skeletal muscle lesions were usu ally mote severe in sheep, particularly in the muscles of the hindquar ters which appeared pale, oedematous and mottled. One of the sheep in the poultry litter dosing trial developed signs of congestive heart fa ilure and the hearts of two others were dilated. Extensive hypertrophy and atrophy of myocardial fibres were evident in the steer fed ad lib . with this material. As in field cases, the myocardial lesions of the sheep were less severe than those of the steer. Mild cardiac dilatati on was present in four of the seven sheep in the maduramicin feeding t rial. Diffuse hypertrophy of myocardial nuclei was present in all seve n cases, myocardial fibre atrophy in six, multifocal fibrosis and necr osis in six and two cases, respectively, and focal endocardial thicken ing in two. The skeletal muscles revealed granular degeneration and fo ci of necrosis acid regeneration. The cardiac and skeletal lesions in the field outbreaks, poultry litter feeding trials and maduramicin fee ding trials, were highly comparable. This suggests that this form of p oultry litter intoxication is a chronic form of ionophore toxicity, th e pathology of which is characterized by a dilated cardiomyopathy with congestive heart failure and mild (cattle) to severe (sheep) skeletal muscle lesions.