Paraquat poisoning in slaughter horses

Fifty Italian draught horses, housed at pasture in semiferal conditions, were examined for excessive weight loss. Among them 4 subjects died and 10 were profoundly lethargic. A mare and foal were examined as they showed seizuring activity and lateral recumbence. Physical examination showed increased cardiovascular and respiratory parameters, whereas other vital signs appeared normal. Bloodwork findings showed anaemia, hypoalbuminaemia, hypocreatininaemia and increased BUN, with no haemoparasites detected. Despite fluid-therapy supplemented with glucose and hepato-protectant compounds, both horses' conditions deteriorated and they were humanely euthanatized. At necropsy, diffuse haemorrhages were detected in lungs, along with oedema, and intestine. The liver was enlarged, firm, with scattered necrotic foci. The kidneys showed cortical hyperaemia and enlargement of the pelvis. Through gas-chromatography analysis of hepatic and renal samples, the metabolite of the herbicide paraquat (N,N'-dymethyl-4,4'-bipiridium dychlorous) was isolated at the concentration of 0.23 mg/L. Upon examination of the pastures, a large area was detected to be recently treated with paraquat. Paraquat is a commonly used, odourless herbicide, not affecting immediately the appearance of treated grass, and it is acutely toxic for horses. The surviving horses were removed from pasture access, stable-housed and orally administered supportive, antioxidant therapy. Follow-up examination, at 15 days, revealed a normal clinical appearance of horses; at 2 months, showed a complete recovery for the whole herd. This report summarizes the paraquat poisoning clinical cases, wherein accurate pasture management appears to be the only strategy for prevention.