Mycotoxins are toxic chemical compounds produced by moulds which are members of the fungi group of plants. Generally speaking, the term mycotoxin is used for moulds that readily and easily colonise crops. Like bacteria, mould spores are ubiquitous in the environment. All herbivores come into close and constant contact with moulds daily - they can be both inhaled and ingested. The mould spores are microscopic and use oxygen to digest organic matter wherever the temperature and humidity levels are sufficient. In optimal conditions, they multiply and form colonies. Their toxic metabolic products are then present in even higher concentrations. The toxins are not needed for their growth or development but are maybe used to depress the immune system of the host plant. This could be a strategy for helping the colony to grow. Toxin production varies greatly with internal and external environmental conditions - there are often multiple toxins produced by the one colony and the same toxins can be produced by other species of mould. While the mould organisms themselves can be killed with heat and digestion, the toxins are very resistant to digestion, heat and cold. 


Aflatoxins - produced by Aspergillus spp - more common in plant products produced in the tropics and subtropics eg. Cotton, corn, peanuts, spices. It can cause liver cancer in animals. Ochratoxins - produced by Penicillium and Aspergillus spp - they can be contaminants in beer, wine and fruit juice. They are mainly nephrotoxic and affect kidney function. Citrinum - produced by Penicillin citrinum - used in cheese making, sake, misot and soy sauce. They can be nephrotoxic in animals. Ergot alkaloids - produced by Claviceps spp - these mostly colonise grasses. Contaminated grain when ingested can lead to symptoms of gangrene or convulsions. Patulin - generally found on mouldy fruit and vegetables - they reduce the efficiency of the immune system. Fusarium - generally found on wheat and corn. Fumonisims affect the central nervous system of horses. Trichothecenes can cause both chronic and potentially fatal toxicities in animals and people. Penicillin - produced by the Penicillium spp - it is a mycotoxic compound of enormous benefit to animal and human life while toxic to bacteria and some other fungi. There are other mycotoxins that are also antibiotics and others that are used for other pharmaceutical benefits. 


Mycotoxicosis is not a single syndrome produced by a relatively small number of moulds with consisitent clinical signs. It is similar to bacteria in that there are a huge number of potential culprits that produce a wide range of health effects. There are non specific signs such as ill thrift, inappetence, depressed immune system, central nervous system abnormalities and possibly behavioural changes. There is no specific blood test for mycotoxins. It would be a diagnosis by elimination of other causal factors that could produce the same signs. Testing the feed with a reputable laboratory would be one possibility to determine the presence and levels of mycotoxins in the feed. It would then have to be interpreted very carefully as to likely results of the ingestion of that level and type of mycotoxin on the horses body. 


Mould can occur in buildings especially where there is humidity and moisture. Stables and sheds should be checked regularly for mould growth. Organic matter is the biggest source of mould - grain, forages, hay, pasture, soil. Mould can occur before and during harvesting and also in storage after processing. Medicinal plants and herbal medicines have also been known to contain mycotoxins. 


It is impossible to eliminate mycotoxins from the environment - over millennia, horses bodies have evolved to deal with constant contact with potentially pathogenic viruses, bacteria, moulds, fungi etc. If the horse is in good physical and mental health it would be harder for the normal background level of mycotoxin exposure to cause a problem. If a horse has become physically stressed with nutritional imbalances, chronic viral or bacterial infections, overwork, lack of sufficient roughage in the diet etc it could be more prone to being susceptible to mycotoxins of a mild to moderate level of intake. If a healthy horse is fed mouldy feed or accesses plants or pastures with high levels of mould then it could succumb to mycotoxicosis. Crop farmers can try and reduce mould levels in crops by crop rotation, soil cultivation, insect and weed control, harvesting earlier and having higher cutting heights. Post harvest grain should be stored in < 13% moisture. If this is not possible, a mould inhibitor should be added to the product. As a horse owner, wet down dusty feed and never feed mouldy hay or grain. Ideally speaking, hay should be fed at least three months after cutting in order for the mould organisms to die. 


Toxin binders are chemical compounds used to absorb myco and endo toxins in the gut before they are absorbed by the body. They then pass out in the manure. They were developed primarily for the chicken, pig and beef industries. Factory farming produces high numbers of intensively raised animals that become incredibly stressed and therefore their immune systems are compromised. A large part of their diet is grain based and mycotoxicosis is a constant risk. These animals need to be constantly growing so any set back with gastro intestinal upsets is to be minimised. They are then slaughtered within a short time frame so there is no real concern for long term possible effects of ingesting toxin binders. Toxin binders can be inorganic (eg bentonite clays) or organic (yeast cell membranes). Their presence is designed to facilitate the attachment of the toxin to the binder and prevent its absorption by the gut. They are not a cure for mycotoxicosis but can be used as part of a treatment programme. 


The efficacy of the active compound should be verified by scientific data. It should have a low effective inclusion rate. It should be stable over a wide pH range. It should have a high capacity to absorb high concentrations of mycotoxins. It should have a high affinity to absorb low concentrations of mycotoxins. There should be affirmation of chemical interactions. It should have proven in vivo efficacy. It should be non toxic and environmentally friendly. It should be known whether it affects availability and absorption of desirable minerals, vitamins, carbohydrates and proteins. Manufacturers should be able to provide strong peer reviewed research supporting their claim for efficacy and safety. 


 More research needs to be done on the horses need for a toxin binder and the efficacy of any that are fed. Anecdotal evidence would possibly suggest that while the acute syndromes of mycotoxicoses are well documented, more rigorous research needs to be done on chronic levels of exposure and likely health and behavioural consequences. Raymond et al (J Animal Science 2003 ; 81: 2123-2130) while performing studies that showed improved feed intake with yeast cell wall extract when fed contaminated feed stated that the long term effects are not clear - maybe use toxin binders with caution long term until further studies are done with horses as opposed to food production animals.