Contaminated feed is being blamed for the deaths of two South Carolina horses and the illness of another.

Farm owner Anne Kennedy said 22 of her own horses and 20 boarded horses reside at Camelot Farms in St. Helena Island, South Carolina. In December a pair of horses residing at the farm began exhibiting coliclike signs. Kennedy said the horses were taken to Edisto Equine Clinic, in Yonges Island, South Carolina, for treatment; the horses later died. Another horse exhibiting similar signs was also taken to the clinic for treatment, Kennedy said.

“But it looks like he is not going to make it,” she added.

Subsequent testing at Michigan State University’s (MSU) Diagnostic Center for Population and Animal Health, in East Lansing, revealed that samples of the horses’ feed were contaminated with monensin, an antibiotic used in ruminants, swine, and poultry that is toxic to horses