Each year, a number of horses die from eating corn or corn byproducts containing fumonisins. Fumonisins are a group of toxins produced by an endophytic mold found within the corn kernel. Typically, fumonisins are produced while the corn plant is growing in the field, but levels can also increase under improper storage conditions after harvest.

Although more than ten types of fumonisins have been isolated and characterized, the most prevalent in contaminated corn is fumonisin B1 (FB1), which is believed to be the most toxic. The dangers from fumonisins are dose-related, and horses and rabbits are the most susceptible of the domestic species. 

Fumonisins can produce the serious neurological disease known as leukoencephalomalacia in horses. Most of the investigated cases of fumonisin poisoning in horses have involved corn screenings.  For this reason, FDA recommends that corn screenings NOT be used in horse feed.  Corn and feed containing corn also needs to be kept dry and protected from moisture when stored to prevent levels of fumonisins and other mold toxins from increasing. FDA recommends that corn and corn by-products used in horse feed should contain less than 5 parts per million (ppm) of fumonisins and comprise no more than 20 percent of the dry weight of the total ration.

In November 2001, CVM and FDA’s Center for Food Safety and Applied Nutrition jointly issued a final guidance for industry on fumonisin levels in human food and animal feeds, which can be viewed at: https://www.cfsan.fda.gov/~dms/fumongu2.html  Additional information about fumonisins is also available at: https://www.fda.gov/cvm/fumonisin.htm