Mycotoxin contamination of grains and forages is a prominent global challenge associated with significant health and performance issues in horses. As herbivores, horses are continuously exposed to various mycotoxins and as post-gastric fermenters, they are susceptible to mycotoxins as monogastric animals. This article will discuss major mycotoxins that present a risk for horses.
Mycotoxins in horses cause immunosuppression, organ damage, colic, poor growth, reduced reproductive performance, and even death. Horses are susceptible to a wide range of mycotoxins including aflatoxins, trichothecenes such as deoxynivalenol, and T-2 toxin, ergot alkaloids, ochratoxin, fumonisins, zearalenone, slaframine, and tremorgenic. However, factors such as age, general health, and immune status affect horse susceptibility to mycotoxins.
Aflatoxins are produced by Aspergillus flavus and Aspergillus parasiticus and they are carcinogenic, teratogenic, hepatotoxic, and nephrotoxic substances. Aspergillus flavus and Aspergillus parasiticus usually form on corn, peanuts, and cottonseeds, and other cereal grains and occasionally on hay and straw. Storing grains at a high moisture level, and failing to clean harvesting equipment, augers, and storage bins before each use enhance the risk for aflatoxin development.
Furthermore, aflatoxin can be transferred in utero from the mare to the foal affecting the biological and immunological responsiveness of neonatal foals.
Trichothecene mycotoxins are the most potent small-molecule inhibitors of protein synthesis, and they include T2 toxin, HT2 toxin, diacetoxyscirpenol, monoacetoxyscirpenol, neosolaniol, 8- acetoxyneosolaniol, 4-deacetylneosolaniol, nivalenol, 4-acetoxynivalenol, deoxynivalenol (DON) or vomitoxin, and 3‐acetyldeoxynivalenol.
The DON is the most common trichothecene produced by Fusarium species in cereal grains in high concentration. The DON is a relatively thermostable compound which is soluble in water.
Information related to the effects of DON on equines and the limiting values or safe concentrations of DON for horses is scarce and inconsistent. Research studies show a large discrepancy between the DON levels causing effects in horses. While some studies imply that horses are not very sensitive to DON, others showed reduced feed consumption at lower levels in corn and wheat (14.9 and 11.8 mg/kg total DON, respectively).
Ergotism Claviceps purpurea and Claviceps paspali exist in the seeds of bluegrass, bromegrass, ryegrass, and in cereal grains such as rye, wheat, and barley and they produce a mycotoxin-containing sclerotia also known as ergot.
Ochratoxins are produced by Penicillium and Aspergillus species and they are nephrotoxic, hepatotoxic, and carcinogenic.
Fumonisins are isolated from Fusarium moniliforme and Fusarium verticillioides cultures and they are identified in 6 different forms (A1, A2, B1, B2, B3, and B4).
Zearalenone is produced rapidly during wet conditions especially in late summer and early autumn by Fusarium fungi.
Slaframine is an alkaloid mycotoxin formed by the fungus Rhizoctonia leguminicola under wet and humid conditions usually in the spring or fall.
Tremorgenic mycotoxins are formed by Claviceps paspali in paspalum grass seedheads, such as Dallis and Bahia grasses. This mycotoxin develops on the lower outer leaf sheath and seeds
Mycotoxins are naturally occurring toxic substances which are produced by moulds and fungi in horse feed. Mycotoxins cause a variety of negative effects in horses including colic, weight loss, reduced feed and water intake, immune suppression, impaired performance, failure in reproductive performance, lethargy, bloody diarrhoea, and liver, kidney, and central nervous system damages. The risk of equine mycotoxin intoxication increases during the spring and summer months when the weather is damp with high humidity. Although further research is required to investigate the stability of toxins in the horse diet to prevent negative impacts on horse health and welfare.
Source: Mycotoxins in the Equine Diet by Amy Parker, M.S.