Stay informed

How mycotoxins affect horses

Author: Dr. Helen Warren, European Technical Manager (Ruminants), Alltech 

What are mycotoxins?

Mycotoxins are toxic chemicals produced by particular mold growth under certain conditions and can occur in growing, harvested or stored cereal and forage crops. However, one of the key difficulties in identifying this risk is that mycotoxins can be present without there being any mold. Equally, not all mold growth indicates the presence of mycotoxins.

There are three major groups of molds that produce mycotoxins affecting horses and other animals: Fusarium, Aspergillus and Penicillium. The first is a field-borne mold, meaning the mycotoxins are usually present when the crop or forage is harvested. The latter two typically form during storage. For example, Penicillium mycotoxins can be seen in poor-quality haylage, especially if air has penetrated the plastic wrap. Effects in the horse vary across the mycotoxin groups, but most are immunosuppressive. Fusarium-derived trichothecenes, such as deoxynivalenol, tend to disrupt normal cell function and affect cells located in the small intestine, liver and immune system. Clinical effects can be reduced feed intake, growth and body weight. Another group of Fusarium mycotoxins is the fumonisins, to which horses appear the most sensitive species. Exposure to fumonisins can result in equine leukoencephalomalacia (ELEM), characterized by depression, ataxia, abnormal behavior, head pressing and often death. The liver can also be involved, and horses generally die within hours of clinical signs.

How do I spot a mycotoxin issue?

Acute outbreaks of mycotoxicosis are rare, and the presence of mycotoxins is more likely to be a chronic issue that manifests over a longer period of time. Some signs that horses may be suffering from mycotoxin ingestion include:

  • General lethargy
  • Unexplained poor performance
  • Reduced feed intake or refusals
  • Inconsistent manure
  • An increased susceptibility to disease
  • Altered heat cycles and swollen mammary glands in mares
  • Joint swelling

Horses are exposed to mycotoxins via feed materials and grazing, as well as bedding. The latter is often over-looked but is also an important consideration. In grazing situaions, both tall fescue toxicosis and perennial ryegrass staggers are linked to mycotoxins produced by endophytic molds on the respective grass species. Lolitrem B is a neurotoxin that causes trembling, muscle spasms and hypersensitivity. All clinical signs can be reversed on removal of the horse from the infected pasture. Red clover can be infected with a particular mold that produces a mycotoxin called slaframine. Slaframine induces diarrhea, feed refusal, respiratory failure, excessive production of tears, abortion and, sometimes, death. It also causes excessive salivation and, hence, the disease is given the name ‘slobbers.’

The concern for horses in relation to mycotoxins is predominantly the effect that consistent, low-level exposure may have on athletic performance and breeding capability without the appearance of any specific symptoms. Unlike commercially bred livestock, horses can have a long lifespan and may, therefore, be expected to reproduce successfully in their later years. For this reason, the relative ‘safe’ level of mycotoxins allowed within the diet is unknown.

Managing the mycotoxin challenge

The effective control of mycotoxins requires taking a multi-faceted approach that includes the management of forage production and storage practices, testing forages and feeds, monitoring animals on a continual basis, and the application of specific nutritional solutions.

Testing forages and feeds with Alltech 37+®

As mycotoxins are both invisible and odourless, specialist detection methods are required to identify the presence of mycotoxins and the levels of contamination. Alltech’s 37+ laboratories test over 7,000 samples of different feedstuffs annually, with each sample being analysed for 54 individual mycotoxins.

More equine-specific research is required, but leading figures in the industry agree that it is an area requiring attention. Suffice to say, all horses come into contact with mycotoxins on a daily basis, and although horses may not be able to avoid exposure to mycotoxins, with good management practices, it is possible to significantly reduce potentially harmful effects.

For more information, or if you would like to submit a sample for mycotoxin testing, please contact