Contaminated feed is being blamed for the recent deaths of dozens of horses at an Oklahoma ranch known for breeding generations of award-winning rodeo livestock.

Feed manufacturer Livestock Nutrition Center claimed responsibility for the deaths on Saturday, saying that a failed cleanup procedure and a sensor malfunction likely caused a contamination of monensin an antibiotic toxic to horses in the feed delivered to Beutler and Son Rodeo Company in Elk City.

Ronnie Castlebury, the president of the feed company, called it an isolated incident and said no other feed has been impacted.