Toxic plants are a concern in equine management as they pose health risks to horses when ingested. These plants contain various compounds that can lead to adverse effects ranging from mild discomfort to severe illness or death. Horses may encounter toxic plants in pastures, hay, or during foraging. Common toxic plants include ragwort, yew, and oleander, each containing specific toxins that affect equine physiology differently. Understanding the identification, distribution, and toxicological impact of these plants is important for prevention and management. This page compiles peer-reviewed research studies and scholarly articles that explore the identification, toxic mechanisms, and management strategies of toxic plants in relation to equine health.
Bauquier J, Takahashi C, Rosales C, Pitt J.There is limited published information on Malva parviflora toxicosis in horses. Four previously reported cases all resulted in death or euthanasia. The aim of this cluster investigation was to describe historical, clinical and clinicopathological findings of four ponies with suspected M. parviflora toxicosis and compare these to previously reported cases. Historical, clinical and clinicopathological findings were collated. Ponies were grazing pasture of approximately >90% M. parviflora. Pony 1 died rapidly without veterinary examination. Pony 2 was examined for prolonged recumbency attribut...
Andrade AC, Fonseca SMC, Silva Filho GB, Melo ET, Santos JRP, Frota MLSL, Duarte JMBS, Evêncio-Neto J, Brito LB, Lima TS, Wicpolt NS, Riet-Correa F....We report an outbreak of Crotalaria juncea intoxication in horses exhibiting progressive weight loss and respiratory distress in northeastern Brazil. Necropsy revealed firm, non-collapsed lungs with extensive interstitial fibrosis, bronchiolar epithelial hyperplasia with club cells proliferation, and marked pulmonary arterial remodeling. Hepatic lesions consisted primarily of centrilobular necrosis, probably resulting from hypoxic injury related to anemia and prolonged agonic death. Pasture inspection identified significant invasion by shrubs of C. juncea in various phenological stages.
Carvalho KS, de Barros CSL, Mendonça FS, Machado M, Riet-Correa F.In Brazil, CNS diseases in equids were little known until the 1980s. Since then, several diagnostic laboratories have been operating in different universities, initially in the South and Southeast regions and, later, in the Central-West, Northeast and North regions. However, the knowledge accumulated from the diagnoses of nervous system diseases of equids made at these institutions over the years has not been reviewed comprehensively, and many papers are published in Portuguese. Here, we review 18 diseases that occur in the nervous system of equids in Brazil, including some critical infectious...
Riquelme LF, de Araújo VO, da Silva TKF, de Sousa MS, da Silva MA, da Silva WDQ, Lucena RB.Malachra fasciata Jacq. (Malvaceae) is an invasive plant widely found in Northeastern Brazil and has been experimentally demonstrated to cause severe dermatitis in sheep. However, its toxic effects in horses have not previously been documented. This report describes primary photosensitization in four Quarter Horses grazing on a pasture heavily infested with M. fasciata in Paraíba, Brazil. Affected animals developed alopecic, erythematous, crusted, and ulcerated lesions on sun-exposed areas, accompanied by severe pruritus and behavioral signs of distress. Histopathology revealed epidermal ulce...
Wickizer LF, Burk SV, Lehman JS.Red maple toxicosis arises when horses consume wilted maple leaves, resulting in methemoglobinemia and hemolytic anemia due to oxidative damage to erythrocytes. Objective: The objective of this study was to determine how maple species (red versus Freeman maple) and horse characteristics, management, and barn site contributed to in vitro methemoglobin production and hemolysis. Methods: Horse information was obtained through an owner questionnaire. Extracts from red and Freeman maple leaves were separately incubated with washed erythrocytes from each horse (n=120). The in vitro percentage methem...
Machado M, Queiroz-Machado CRR, Queiroz F, Gardner DR, Riet-Correa F.A Mimosa pudica var. unijuga-associated toxicity affecting horses occurred in Araguari, Triângulo Mineiro, Southeast Brazil. Affected horses had gradual hair loss of the mane and tail and endocrine dermatosis after grazing for three months during the dry season on a paddock invaded by the plant. The main histological lesions include compact ortho-keratotic hyperkeratosis and numerous flame follicles. Toxicological analysis by HPLC-UV demonstrated 0.8 mg/g of mimosine in the leaves.
Stegelmeier BL, Davis TZ.Many toxic plants are unpalatable to horses and are not eaten when alternative forage is available. However, when such plants contaminate prepared or baled feed and forage, herd competition and improved palatability can alter acceptance and thereby cause equine plant poisonings. Dehydropyrrolizidine alkaloid-containing plants; cocklebur; Salvia reflexa; kleingrass, switchgrass, and other saponin-containing grasses; jimson weed, black henbane, and other tropane alkaloid-containing plants; lantana; Cassia spp and other myotoxic plants; castor bean; cyanogenic glycoside-containing plants; thiamin...
