Abstract:
This report contains an account of the gross and histopathological lesions of 20 cattle and four sheep in 15 field
outbreaks of poultry litter toxicity, one steer fed ad lib. and six sheep dosed with toxic poultry litter, and ten sheep
fed experimental rations containing c 2,5 ppm and 5 ppm maduramicin.
The principle macroscopic lesions in most cattle that died in field outbreaks were indicative of congestive heart
failure. The lesions in sheep were similar, but generally milder. Cardiac dilatation was observed in both sheep and
cattle. Microscopically, the cardiac lesions were more pronounced in cattle and comprised varying degrees of
atrophy, hypertrophy, degeneration, necrosis of myocardial fibres, and interstitial fibrosis. Skeletal muscle lesions
were usually more severe in sheep, particularly in the muscles of the hindquarters which appeared pale, oedematous
and mottled.
One of the sheep in the poultry litter dosing trial developed signs of congestive heart failure 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 dilatation was present in four of the seven sheep in the maduramicin feeding trial. Diffuse hypertrophy
of myocardial nuclei was present in all seven cases, myocardial fibre atrophy in six, multifocal fibrosis and necrosis
in six and two cases, respectively, and focal endocardial thickening in two. The skeletal muscles revealed granular
degeneration and foci of necrosis and regeneration.
The cardiac and skeletal lesions in the field outbreaks, poultry litter feeding trials and maduramicin feeding trials,
were highly comparable. This suggests that this form of poultry litter intoxication is a chronic form of ionophore
toxicity, the pathology of which is characterized by a dilated cardiomyopathy with congestive heart failure and mild
(cattle) to severe (sheep) skeletal muscle lesions.
