Six horses killed by errant drug in feed

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Six horses died after eating feed contaminated with a cattle-use drug.

Employees of a feed maker, Gilman Co-op Creamery in Gilman, Minnesota, failed to clean equipment after making a batch of cattle feed containing monensin, an antimicrobial that is toxic to horses in low doses, according to the Food and Drug Administration. The horse feed was a custom order, delivered to only one place.

The owners of the horses began giving the animals the feed on June 9, and one horse became unable to stand the same day. That horse was euthanized two days later.

Two more horses were unable to stand on the third day, and both died by the fourth day. Three more died within a month.

Monensin is an ionophore-class antimicrobial, given to cattle and poultry in feed for production and disease prevention. In horses, toxic effects consist of weakness, unsteady gait, diarrhea, abdominal pain, excess urination, and heart failure. But the drug also can kill quickly, with few clinical signs.

Few monensin poisonings in horses are treatable and most are fatal, FDA information states. Surviving horses can have lasting damage to their heart and other muscles.