In August of 2008, a 200-head commercial beef cow-calf operation started experiencing acute deaths of cows and calves. A total of 24 cows and 11 calves died over a four-day period. There was a flash flood at the ranch where “bottom” land flooded one week prior to the start of deaths. There was also Perilla mint present that had evidence of the tops of the plants being grazed.

The cattle had not been processed recently other than to pen and sort off a few calves for marketing. All of the dead animals except one were cows from a group purchased in March or their spring calves. All calves (born to original herd and additions) had been vaccinated once with blackleg vaccine in March. The cows in the original herd were vaccinated by the previous owner as calves. It’s not known which product was used or if it was properly boostered. The new adult cows’ vaccine status was not known, but they came from the same source as original herd, so it was assumed they were vaccinated as calves also.

There were no gross lesions in any of the calves that were necropsied. Gross lesions in the cows varied from none, to subtle to severe. Black, edematous lesions in the muscles of the shoulder and neck area were present. There was also mild pulmonary edema/emphysema in some cows.

Clostridium novyi infection was confirmed by florescent antibody tests on impression smears of muscle. Lesions of acute bovine pulmonary edema and emphysema (ABPE) consistent with Perilla mint toxicity were found on histopathology of the lungs. It is possible that Perilla mint ingestion caused mild ABPE, which lead to some degree of hypoxia that predisposed the cattle to the clostridial myositis.

We can only speculate as to why except for one, only the cattle added to the herd in March and their calves were affected. Plant toxicities commonly occur more frequently in cattle that are new to an area while native cattle that have had access to the same plants for years are less likely to ingest toxic amounts. It’s also possible that the immunity to clostridial diseases differed in the two groups.

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This case study was submitted by Christine Navarre, DVM, MS, DACVIM Louisiana State University.