The Dark Side of Grasslands: Endophyte Toxicosis in Horses—Exposure Risks, Health Consequences, and Management

Grasslands are the cornerstone of horse feeding, used for grazing and to produce roughages and their products. However, improper grassland management hides several threats for equine health. In this context, grasslands contaminated with toxin-producing endophytes are considered an increasing threat for horses in many parts of the world. Endophytes are fungi that may grow in a mutualistic relationship in a range of grasses, including fescue grass and perennial ryegrass, two foliage species commonly found in European and American meadows and pastures. The endophytes produce alkaloids that are highly toxic to insects and animals, including horses. Among the four types of endophyte alkaloids, namely peramine, loline, indole diterpene, and ergot alkaloids, the latter two are known to be (neuro)toxic to horses. Recent research indicates that increasing concentrations and co-occurrence of ergot alkaloids and indole diterpene in horse pastures and meadows, especially during hot and arid summer months, increase the risk of endophyte toxicosis in horses. The main aim of this review article is to summarize the most recent knowledge on endophytic alkaloids of grasslands and products thereof, and the resulting endophyte toxicosis in horses, focusing mainly on the exposure risks, symptoms and management strategies.