GILMAN (AP) -- The U.S. Food and Drug Administration is investigating the deaths of six horses at a farm in central Minnesota that it has linked to some tainted feed.

The FDA says the feed came from a single batch of feed from the Gilman Co-Op Creamery in Gilman. The agency says the feed contained monensin, an animal drug toxic to horses. The feed was a custom blend for the farm and was not distributed to other locations. The FDA says the creamery operators did not properly clean the equipment to remove any traces of monensin before mixing the feed for the unnamed farm. The horses died in June and July.

Gilman Co-Op general manager Adam Bonovsky says the allegations made by the FDA have not been proven. Bonovsky says lab results on the feed have not yet been returned.