Toxic feed constituents in the horse.

Poisoning cases in horses associated with dietary exposures can encompass a wide variety of etiologies that can be caused by natural or man-made components. Feed mixing errors and ingestion of feed formulated for other species are the most common means by which poisonings from man-made materials occur. Ionophore feed additives and antibacterial agents are especially toxogenic to horses. Effects of ionophores in horses include clinical, clinicopathologic, and pathologic changes associated with cardiac, muscular, and neurologic tissues involvement. The acute effects of ionophores, however, can result in long-term cardiac dysfunction. Antibacterial effects are associated with changed microbial populations in the digestive tract that results in bacterial toxin liberation. These bacterial toxins damage the mucosa, and they result in systemic effects. For either type of feed-associated poisoning, it is critical that samples be analyzed for an accurate diagnosis.