Mycotoxin Feed Contamination Poses Health Risks for Horses

Learn about the potentially serious horse health problems mycotoxins and metabolites produced by mold can cause.

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Most feed tags include a statement cautioning against offering moldy feed or hay to horses. Owners might suspect mold when they see white, blue, or greenish powdery substances in hay or feed; black spots on hay; or simply by detecting a musty smell in damp, heavy hay. It is crucial to notice mold and avoid feeding molded feedstuffs because the fungus itself—or organisms it produces—have the potential to cause illness and even death in horses.

So what exactly is mold? Mold is a type of fungus, and the number of different molds is estimated in the hundreds of thousands of species. Some molds are harmless; others are useful and even edible. For instance, blue cheese is made by adding a particular Penicillium mold culture to cheese, while another Penicillium species is used to produce antibiotics. And in Asia the mold Aspergillus oryzae has been used for many centuries to ferment a soybean and wheat mixture to make soy sauce or to break down the starch in rice to make sake and other distilled beverages. So why is moldy hay or feed harmful to horses?

Because molds consume nutrients from the host plant material, reducing the nutritive value of moldy feed or hay. Molds can also be allergenic, causing irritation to the lungs, digestive tract, or skin. Certain molds produce secondary metabolites called mycotoxins, which can be found in any animal or human foodstuff that has previously supported growth of specific fungi. Molds and their associated mycotoxins are present in varying amounts depending on climatic growth and storage conditions. Cool, wet growing seasons lead to increased fungi growth, especially of the genus Fusarium, in grains. High moisture levels support fungal growth, and cool temperatures can promote mycotoxin production. Hay baled with moisture content greater than 15% is more likely to develop mold, giving way to mycotoxin proliferation

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Written by:

Karen Davison, PhD, is an equine nutritionist and sales support manager for the horse business group at Purina Animal Nutrition. Her expertise includes equine nutrition, reproduction, growth, and exercise physiology. She received her MS and PhD from Texas A&M University.

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