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Effects of mycotoxins in horses

Studies on mycotoxins in horses are scarce and most of these are published in  lower impact horse industry specific journals. Horses are post-gastric fermenters, meaning that the enzymatic digestion is followed by fermentation. This makes them as susceptible to mycotoxins as monogastric animals.

Mycotoxins can cause immunosuppression at levels that are undetectable by routine screening methods

Professor Vincent Cheng
Aflatoxin B1


Aflatoxins are carcinogenic, teratogenic, hepatotoxic and nephrotoxic substances.5,6,7,8 These mycotoxins suppress the immune system, rendering the animal more sensitive to the attack of pathogens and decreasing vaccine and therapy efficiency.5,6,7,8 Possible negative effects on horses include reduced feed intake and performance, feed refusal, liver complications (icterus), kidney damage, decreased resistance to environmental and microbial stressors, higher susceptibility to diseases.2,13 The transfer in utero from the mare to the foal can affect the biological and immunological responsiveness of neonatal foals.13


Ergot alkaloids

Horses can be exposed to complex mixtures of ergot alkaloids. Ergot alkaloids are vasoconstrictive and neurotoxic and can cause reproductive failure. Possible effects on horses include ear, tail and hoof necrosis; lameness. Negative effects that have been observed in mares include reproductive disorders; signs of estrus; stillbirths; reduced pregnancy rate; abortions; prolonged gestation; poor mammary gland development; prolonged uterine involution; placental and fetal abnormalities; obstructed labor; low prolactin and colostrum production; agalactia and staggers.3,6 Ergot alkaloids produce a series of effects that are specific to foals. Among these the most common are: respiratory failure, skin, umbilicus, bone, muscle abnormalities, blindness, testicular atrophy and decreased immunoglobulin (Ig) concentration.6

Fescue toxins can also affect horses. Effects of these toxic metabolites include immunosuppression (increased susceptibility to diseases and deceased resistance to environmental and microbial stressors), neurotoxic effects and reproductive effects.2,9 In pregnant mares, fescue toxins cause extended gestation, thickened placenta and agalactia.2,9

Fumonisin B1


These mycotoxins are the most detrimental for horses – with fumonisin B1  (FB1) being the worst - particularly due to their effects on the central nervous system, liver and heart.3,6,14 A clinical sign of fumonisin poisoning is the development of equine leukoencephalomalacia (ELEM), liquidification of the brain which leads to death, and results in depression, ataxia, anorexia, incoordination, hyper excitability, sweating, blindness, death.14 Other negative effects include, immune suppression, decreased performance, liver damage, jaundice, increased susceptibility to secondary infections.



Trichothecenes generally interfere with DNA replication and therefore protein synthesis. Due to the importance of proteins in living organisms, trichothecenes can have a negative impact on many vital processes and organs.5,7,8

Type A Trichothecenes

Type A trichothecenes like T-2 toxin are immunosuppressive and can cause changes in the leukocyte count as well as reduce antibody formation.5,7,8 Effects on horses include less resistance to environmental and microbial stressors, increased susceptibility to diseases, decrease of immune cells, reduced performance, feed refusal, decreased growth, hemorrhage, bloody diarrhea, oral and dermal lesions and tail necrosis.2,12

Type B Trichothecenes

Contamination of feed with type B trichothecenes like deoxynivalenol is associated with reduced feed consumption, gastrointestinal alterations such as diarrhea and colic that leads to decreased performance have also been observed.1,3,5 Other symptoms include immunosuppression, impaired gut health, decreased resistance to environmental and microbial stressors, increased susceptibility to diseases.2,3,12


Ochratoxins are nephrotoxic, hepatotoxic and carcinogenic.4 Ochratoxins cross the placental barrier in mares and therefore affect the fetus.11 Other negative effects include kidney damage, increased water consumption, kidney and bladder dysfunction, liver damage, diarrhea and immune suppression.3,4  



Zearalenone (ZEN) causes estrogenic effects in horses and is responsible for severe reproductive disorders. In pregnant mares, it increases the occurrence of abortions and stillbirths. Other negative effects include reproductive failure and impaired semen quality. 8,10  

Effects of mycotoxins in horses
AFB1 – Aflatoxin B1 | AFM1 – Aflatoxin M1 | DON – Deoxynivalenol | FUM – Fumonisins | OTA – Ochratoxin A | T-2 – T-2 Toxin | HT-2 – HT-2 Toxin | ZEN - Zearalenone | Ergots – Ergot, Alkaloids
  1. Antonissen G., Martel A., pasman F., Ducatelle R., Verbrugghe E., Vandenbrouke V., Shaoji L., Haesebrouck F., Van Immerseel F., Croubels S. (2014). The Impact of Fusarium Mycotoxins on Human and Animal Host Susceptibility to Infectious Diseases. Toxins (6) 430-452
  2. CAST Report (2003). Mycotoxins: risks in plant, animal, and human systems (Richard, J. L and Payne, G. A. eds.) Council for Agricultural Science and Technology Task Force report No. 149, Ames, Iowa, USA.
  3. Franklin RC, Rivero R, Odriozola E, de Lourdes Adrien M, Medeiros MTR, Schild AL (2014). Mycotoxicoses of ruminants and horses. Journal of Veterinary Diagnostic Investigation 20(10) 1–17.
  4. Frantisek M., Ostry V., Pfohl-Leszkowicz A., Malir J., Toman J. (2016). Ochratoxin A: 50 Years of Research. Toxins (8) 191.
  5. Grenier B., Applegate T.J., (2014). Modulation of Intestinal Function Following Mycotoxin Ingestion: Meta-Analysis of Published Experiments in Animals. Toxins (5) 396-430.
  6. Krska R., Nährer K., Richard J. L., Rodrigues I., Schuhmacher R., Slate A. B., Whitaker T. B., (2014). Guide to Mycotoxins featuring Mycotoxin Risk Management in Animal Production. BIOMIN edition 2014
  7. Lemmens M., (2016). Mycotoxin Summer Academy – Module 1. IFA Tulln
  8. Marin S., Ramos A.J., Cano-Sancho G., Sanchis V., (2014). Mycotoxins: Occurrence, toxicology, and exposure assessment. Food and Chemical Toxicology (60) 218-237
  9. McDowell KJ, Moore ES, Parks AG, Bush LP, Horohov DW and Lawrence LM (2014). Vasoconstriction in horses caused by endophyte-infected tall fescue seed is detected with Doppler ultrasonography. Anim Sci, 91:1677-1684.
  10. Minervini, F., Giannoccaro, A., Fornelli, F., Dell'Aquila, M. E., Minoia, P. and Visconti, A. (2006). Influence of mycotoxin zearalenone and its derivatives (alpha and beta zearalenol) on apoptosis and proliferation of cultured granulosa cells from equine ovaries. Reprod. Biol Endocrinol. 30; 4:62.
  11. Minervini F, Giannoccaro A, Nicassio M, Panzarini G and Lacalandra GM (2014). First Evidence of Placental Transfer of Ochratoxin A in Horses. Toxins 5, 84-92
  12. Sharma, R. P. (1991) Immunotoxic effects of mycotoxins. In: Mycotoxins and Phytoalexins (Sharma, R. P. and Salunkhe, D. K., eds.), pp. 81-99. CRC Press. Boca Raton, Florida.
  13. Vesonder, R., Haliburton, J., Stubblefield, R., Gilmore, W. and Peterson, S. (1991). Aspergillus flavus and aflatoxins B1, B2, and M1 in corn associated with equine death. Arch. Environ. Contam Toxicol. 151-153.
  14. Voss K.A., Smith G.W., Haschek W.M. (2007). Fumonisins: Toxicokinetics, mechanism of action and toxicity. Animal Feed Science and Technology (147) 299-325.