Monensin is an animal drug approved for use in cattle, swine, and poultry that is highly toxic and potentially lethal to horses, even at relatively low levels; it sometimes contaminates nonmedicated horse feeds produced after medicated feeds for other livestock. | Photo: The Horse Staff

On Oct. 17 the U.S. Food and Drug Administration (FDA) announced it had issued warning letters to two feed mills—Gilman Co-Op Creamery, in Gilman, Minnesota, and Farmers/Ranchers Cooperative Association of Ainsworth, in Ainsworth, Nebraska—regarding monensin contamination in horse feed they produced.

Monensin is an animal drug approved for use in cattle, swine, and poultry that is highly toxic and potentially lethal to horses, even at relatively low levels.

The FDA said these firms did not adhere to the Current Good Manufacturing Practice (CGMP) requirements for medicated feed mills. They are also subject to FDA’s Preventive Controls for Animal Food regulations. The medicated feed CGMPs require firms to conduct appropriate sequencing or adequate equipment cleanout procedures when switching from mixing a medicated animal food to a non-medicated one. These regulations are designed to prevent unsafe cross-contamination between medicated feed and nonmedicated feed or other medicated feed