A horse and three ponies have died, and several other equids have been temporarily paralyzed, following the ingestion of contaminated feed in French Guiana (a department of France located on the northern edge of South America), according to the departmental director of veterinary services in Cayenne.

Arnaud Martrenchar, DVM, PhD, said that animals in two separate locations suffered “violent symptoms” of paralysis and hepatitis within 24 hours of eating a commercial supplement from a single common bag. The feed had been accidentally contaminated with salinomycin, an ionophore which is often added to poultry feed. The feed manufacturing company, Le Gouessant, based in northwestern France, announced the discovery of their error in late November.

Jean-Charles Oisel, head of communications at Le Gouessant, explained that factory workers had confused the salinomycin additive, coded HYPER 605 SA, with the proper additive, coded HYPER 605.

However, serum analyses of the affected equids, performed at the Institut Pasteur in Paris, also revealed the presence of type D botulinum toxins, suggesting a likely combination of factors leading to the animals’ reactions.

“No single toxin can explain these symptoms,” Martrenchar said. Primary analyses of the contaminated feed revealed no presence of botulinum toxins, but these results remain inconclusive, Martrenchar said.

Ionophore toxicity is rare, although monensin, an ionophore used in cattle feed, causes more toxicity cases in equids than salinomycin, said Monica Aleman, MVZ, PhD, Dipl. ACVIM, of the Veterinary Medical Teaching Hospital at the University of California, Davis.

Accidents at the feed mill are sometimes to blame, she said, but poisoning probably happens more frequently when horses wander into the feed storage area and help themselves to the wrong bag.

“However, a mixing error from feed companies would have mor