What is the threat?
For horse owners, the key difficulty in identifying risk is that not all moulds produce mycotoxins, but those moulds that do may die off leaving no visible indication of contamination. We must realise therefore, that just as we live with various strains of bacteria, so we must expect to come into contact with mycotoxins and, just as some bacteria have the ability to cause harm in certain circumstances, so high levels of exposure to mycotoxins, or exposure in more vulnerable equines, can result in some sort of negative reaction.
Mycotoxins have been shown to suppress the immune system and, while severe mycotoxin poisoning (mycotoxosis) can be fatal, moderate exposure has been linked to hypersensitivity and allergies, poor growth rates in youngstock, reduced performance levels, liver damage and loss of condition. Some studies have also cited mycotoxins as a possible factor in grass sickness and colic. Certain types of mycotoxin have been shown to have an antibiotic effect; which is undesirable, since antibiotics knock out beneficial bacteria in the gut, resulting in digestive disorders such as scouring or colic. Long term exposure to mycotoxins can, therefore, prove debilitating and leave the horse vulnerable to sickness or disease
High risk groups include those whose immune system may already be under pressure, including youngstock, broodmares, veterans, performance horses, poor doers or sick and convalescing equines. Horses used for competitions such as racing, eventing, dressage, polo, long distance riding and show jumping are high value animals and economic losses from reduced performance and health problems due to mycotoxins may be significant. These horses are extremely fit and therefore subject to higher levels of stress not only from the high work level, but also travelling and competing. This has a negative effect on the immune system, which consequently may be more susceptible to the effects of mycotoxins. Mycotoxins are also known to negatively affect reproductive performance in breeding stock.
Mycotoxins exert their effects on horses through four primary mechanisms:
- Intake reduction or feed refusal
- Alteration in nutrient content of feed in terms of nutrient absorption and metabolism
- Effects on the endocrine system
- Suppression of the immune system
