Contaminated feed is responsible for the recent deaths of dozens of horses at an Oklahoma ranch known for breeding award-winning rodeo animals.

Feed manufacturer Livestock Nutrition Center took responsibility for the animal deaths Saturday, saying a “failed cleaning procedure and sensor failure” likely caused contamination with monensin — an antibiotic toxic to horses — in feed delivered to Beutler and Son Rodeo Company in Elk City.

Ronnie Castlebury, president of the feed company, called it an isolated incident and added that “no other feed was affected.”

“Words mean nothing, but we are committed to helping and supporting the Beutler family and making amends because our customers and employees expect and deserve it,” Castlebury said.

The Oklahoma Department of Agriculture, Food and Forestry confirmed to HuffPost on Wednesday that its investigation into the matter, which involves the Kansas Department of Agriculture and the U.S. Food and Drug Administration, is ongoing.

The spokesman said ODAFF was awaiting results from tests conducted on feed samples taken from the ranch last week. Since the investigation began, it has not received any calls, complaints or messages related to the feed from other customers.

The department previously said it was investigating the deaths and analyzing a feed sample using two state-certified labs after being contacted by a veterinarian on Aug. 23 about the illnesses.

The Kansas Department of Agriculture told HuffPost last week that it was reviewing the feed company’s records, as well as its labeling and operating procedures, “to ensure proper feed protocols are being followed.” A spokesperson for the department did not immediately respond to a request for comment Wednesday.

Initial reports suggested that monensin, also known by its trade name Rumensin, might be to blame. The drug is used as a feed ingredient for farm animals such as cattle, sheep, goats and chickens, but is toxic to horses and pets.

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