Doxycycline toxicity caused by a large overdose (10 times the therapeutic dosage) in two feedlots is described. The clinical symptoms occurred after 2–3 days and mortality 5 days after the onset of the medication which was added to the milk replacement.
Mortality reached 25% (five calves) and 27% (seven calves) in herds A and B, respectively.
Pathological and histological findings revealed pulmonary oedema, myocardial degeneration and necrosis. These findings confirm the cardiovascular toxicity, caused apparently by doxycycline administration to the calves, and indicate the potential side-effects of this drug in cattle.