The Food And Drug Administration (FDA) has issued a reminder to horse owners of the danger that fumonisins, mold toxins most frequently found in corn, pose to horses. ”Moldy corn poisoning” causes irreversible and fatal damage to the brain. Horses are particularly sensitive to this fungal toxin.
The FDA had previously issued guidelines for feed manufacturers regarding upper safe limits of fumonisin B, considered to be the most toxic. Most large manufacturers routinely test, but small local operations may not. If your horse’s grain mixture contains corn, it’s wise to ask the manufacturer if they test.
Obviously moldy feed should never be fed, and if your horse is reluctant to eat a feed even if you can’t see anything wrong with it, don’t try to flavor or otherwise alter it to make him eat it. The horse may well know best. With fumonisin/moldy corn poisoning, a fatal level of toxin may be present without either you or the horse being able to tell there’s anything wrong with the feed.
Molds require warm temperatures and moisture to grow with pelleted/processed feeds molding easier in storage than grains because of the steam used in their processing. However, the problem often starts when the grain is still in the field, especially in droughts.
If you are feeding certified organic products, periodically send your feed for a fungal toxin screen. These are available through feed/forage testing laboratories, such as Litchfield (www.litchlab.com, 517-542-2915), and will be listed under ”Mycotoxin Screen.”
There are many other types of mold/fungal toxins, with well described negative effects in other species but not often well studied in the horse. Some of the most recent information on these includes:
• 2006 report from the National Research Council in Italy found that the common mold toxin zearalenone and its derivatives have a strong effect on ovarian cells in the lab and postulated that exposure to these toxins could cause failure to ovulate.
• 2005 study from the University of Guelph fed mares a diet contaminated with fusarium mold species toxins for 21 days. Horses were also exercised throughout that time and had an exercise test to fatigue at the end of the 21 days. Half of the horses had glucomannan also added to their feed, at a rate of 0.9 grams per pound. Glucomanna is marketed as a mold toxin binder. Control horses were fed toxin free grains. All horses fed with contaminated grains ate less than control horses. There was no effect on athletic performance at the levels fed for a 21-day period. The glucomannan did not protect for appetite suppression.
• A 2003 21-day feeding, also done at the University of Guelph, fed grains that had somewhat higher levels of fusarium toxins and the same level of added glucomannan and found that the degree of appetite suppression was less when glucomannan was added. That study also looked at blood changes and found the toxins increased the levels of liver enzymes for the first two weeks of feeding, but that those enzyme rises returned to normal at the three-week mark, indicating the liver had responded to the toxin challenge successfully. The glucomannan was found to also decrease the magnitude of the liver enzyme rise.