Poisonous plants and phytotoxicoses in horses (review)

A large number of plants contain chemical compounds that have a toxic effect on animals (E.M. Kurenkova et al., 2018). Feed-born phytotoxins cause severe pathology in horses. Phytotoxins are diverse in species composition, distribution, mode of action and lethal effect. Poisoning of horses by poisonous plants is a relatively common veterinary problem that can occur when a fresh plant is ingested by an animal on pasture or when the plant contaminates hay, silage and other feed (F. Caloni et al., 2015). Plant toxicity is also a serious problem, as animal poisoning results in significant economic losses (L. Curtis et al., 2019). Depending on the degree of toxicity and the amount of plant eaten, the effect varies from mild illness to disruption of the activity of organs and body systems, which can lead to animal death (M. Wickstrom, 2002). Poisoning caused by poisonous plants is difficult to diagnose and differentiate from other pathologies, since clinical signs are usually not specific and can be observed in other diseases (K.E. Panter et al., 2012). Data on the true incidence of equine poisoning by plant toxins are sparse or absent due to lack of centralized poisoning reporting and monitoring system in place (K. Welch, 2019). Despite the fact that most toxic plants have an unpleasant taste for horses, there are many factors that increase the risk of poisoning, e.g., the influence of the growing season on the taste of some poisonous plants, lack of feed on pasture, toxic plants getting into the hay, monotonous habitat, curiosity, etc. (F. Caloni et al., 2015). It is important to constantly update the knowledge of veterinarians and animal owners about the poisonous plant diversity, phytotoxins, and phytotoxicoses. The review summarizes the most common plant species in Russia which causes poisoning in horses. The places are indicated where plants that are poisonous to horses grow, the mechanisms of action of the toxic substances they contain and their clinical effects in animals are described in detail, including disturbances in the digestive, cardiovascular, excretory, respiratory and nervous systems and many other sings. Poisonous plants are classified according to the mechanism of action of toxic substances into groups containing alkaloids, neurotoxins, photosensitizing substances, cyanogenic glycosides, and cardiac glycosides (M.I. San Andrés Larrea et al., 2024). The need for careful monitoring of the botanical composition of pastures and hay, and avoiding accidental consumption of poisonous plants by horses, is emphasized.