Equine Moldy Hay and Feed Toxins – NAVLE Study Guide

Overview and Clinical Importance

Feed-related toxicoses represent a significant category of equine multisystemic disease on the NAVLE. Horses are uniquely susceptible to several feed contaminants due to their sensitive gastrointestinal physiology and metabolic pathways. Mycotoxins, ionophores, and endophyte alkaloids are the three major categories of feed-borne toxins that veterinarians must recognize and manage. These conditions often present with nonspecific clinical signs initially, making a thorough dietary history essential for diagnosis.

Understanding the source, mechanism, clinical presentation, and management of these toxicoses is critical for both clinical practice and board examinations. Horses are extremely sensitive to ionophores (20 times more than cattle) and fumonisins, making feed contamination potentially fatal even at low concentrations.

Mycotoxins in Equine Feed

Mycotoxins are toxic secondary metabolites produced by filamentous fungi. The major mold genera producing mycotoxins relevant to equine health include Fusarium, Aspergillus, and Penicillium. Fusarium toxins typically develop in the field during cool, wet conditions, while Aspergillus and Penicillium toxins form during improper storage in warm, humid environments.