Molds are one-celled fungi that facilitate the breakdown and decay of plant materials. Mycotoxins are "sporadically produced secondary metabolites of molds," according to Equine Clinical Nutrition by Lon D. Lewis, DVM, PhD, Dipl. ACVIM. Antibiotics (such as penicillin) are types of useful mycotoxins, which at therapeutic levels are more toxic to bacteria than to animals. There are other types of mycotoxins that can be harmful or fatal to horses.

Some fungi live inside plants in a symbiotic relationship. They make the plant more resistant to drought, frost, and insect infestation while they derive nutrients from the host plant. Many of these affected plants are forages and feedstuffs that horses consume. Under optimum conditions (usually including high moisture), mycotoxins can form in plants within hours, and they can reach maximum concentration within one to two weeks.

What are Mycotoxins?

Horses have an increased risk of encountering mycotoxins when fed grain products, which readily support fungal growth. Kyle Newman, PhD, is director of Venture Laboratories, an analytical lab for the feed industry and author of The Mycotoxin Blue Book. He explains that mycotoxin contamination has been detected in feeds, forages, and bedding