Case report

Blister beetle poisoning (cantharidiasis) of dairy and beef cattle

Abstract

Blister beetle poisoning (cantharidiasis) of horses has been well documented. Primary exposure to blister beetles is through consumption of contaminated lucerne hay. Confirmed cases of bovine cantharidiasis due to natural exposure have not previously been documented in veterinary literature. This report describes four cases of blister beetle poisoning in three dairy herds and one beef herd in New Mexico and Oklahoma, USA, that were reported between 1995 and 1999. Cows in two large dairy herds consumed blister beetles in a total mixed ration containing green chop lucerne. The most significant clinical signs were mass refusal to eat the freshly cut green chop lucerne, although the cows appeared hungry, and the corresponding dramatic decrease in milk production. Cows in a smaller dairy herd and a beef herd consumed large round bales of lucerne hay containing blister beetles. In contrast to cows exposed to the beetles in green chop, feed refusal in these cases was limited to individual cows. Other clinical signs included salivation, bruxism, frequent urination, diarrhoea, reluctance to move, abdominal pain, ataxia and recumbency. Postmortem examination did not reveal significant gross or microscopic lesions. Cantharidin was detected by gas chromatography-mass spectrometry analysis of either urine or feed samples. In addition, blister beetles were found in the lucerne green chop or hay.