Life-Threatening Fumonisins in Horses

Fumonisins are dangerous mycotoxins sometimes found in feed. Here’s what to watch for and how to protect your horse.

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Fumonisins are mycotoxins, which are harmful secondary compounds that specific molds and fungi produce in soils, grains, and forages when moisture levels permit. This mycotoxin variety is produced by Fusarium verticillioides, F. proliferatum, and other Fusarium fungal species. Animal and human health problems related to fumonisins are most commonly associated with the consumption of contaminated maize (corn) or products made from maize.

Horses have a longer life span than many other livestock, some living 30 years old or more, so their exposure to toxins can be long-term. Horses used for competitions are often high-value animals and economic losses from poor performance, health problems, and even loss of use due to mycotoxins can be significant.

Fumonisin Levels Guided by the FDA

Consumption of moldy maize has long been recognized as a cause of equine leukoencephalomalacia (ELEM, often referred to as moldy corn poisoning). Fumonisins B1 (FB1) have been shown to be cardiotoxic (they damage the heart muscle) and cause pulmonary edema in pigs. Cattle and poultry are considerably less sensitive to fumonisins than horses and some other species, including pigs, rabbits, and laboratory rodents. The U.S. Food and Drug Administration (FDA) Center for Food Safety and Nutrition has issued guidance levels for fumonisins in maize and maize byproducts used in animal feeds. The levels vary by animal species, reflecting their relative sensitivities to fumonisins:

FDA guidance levels for total fumonisins (FB1+FB2 +FB3) in animal feed1

Species Feed factor2 Total fumonisins in maize or maize byproduct in formulated feed Total fumonisins in formulated feed
Horses/other Equidae 0.2 53 1
Rabbits 0.2 5 1
Canines/felines/all other4 0.5 10 5
Catfish 0.5 20 10
Pigs 0.5 20 10
Lactating cows 0.5 30 15
Breeding stock 0.5 30 15
For slaughter 0.5 60 30
Layers 0.5 30 15
Breeders 0.5 30 15
For slaughter7 0.5 100 50
Mink 0.5 60 30
1—Adopted from Center for Food Safety and Nutrition (2001).
2—Percent of formulated ration composed of maize or maize byproduct.
3—Maize screenings not to be included in rations for Equidae.
4—Other species not listed in table.
5—Includes beef cattle, sheep, goats, and other ruminants.
6—Includes chickens, turkeys, ducklings and other poultry species.
7—Animals ≥3 months of age.

Fumonisins in Horses

Horses are the most sensitive of these species to fumonisin toxicity, and disease occurs worldwide. Most damage occurs in horses’ hearts, central nervous systems, and livers. The rare surviving animals usually have permanent neurologic damage

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