1998 Drought Information - Mycotoxicosis

Most Frequently Asked Questions on Mycotoxicosis in Horse Feeds

David W. Freeman
OSU Extension Equine Specialist

MYCOTOXINS ARE produced by molds. These can be beneficial agents such as penicillin, however, most requests for information on mycotoxins refer to those mycotoxins in feedstuffs that are harmful to horses. Some of the more commonly occurring clinical signs of mycotoxicosis that sporadically occur in feeds of horses are summarized below.

Equine Leukoencephalomalacia (ELEM, moldy corn disease, fumonisin toxicosis)
The fusarium mold produces the mycotoxin fumonisin. It is associated with feeding corn containing fumonisin, hence the name moldy corn disease. Poorly stored corn and drought stressed corn cause an increase incidence and need for awareness for the prevalence of this mycotoxicosis. The incidence of fusarium problems increased a couple of years ago when corn was in short supply. The problems were most associated with use of corn screenings.

When other mold probems such as aflatoxins are heightened, feed companies should test corn used in horse feeds through use of on site tests and laboratory analysis. Problems can occur without obvious visual mold growth.

The Oklahoma Animal Disease Diagnostic Laboratory (OADDL) at OSU tests for fumonisin. Clinically, the toxicosis results in blind staggers (ataxia) and other observable signs of neurological degradation, and most often results in death. Treatment includes 1) preventative measures to decrease potential of ingestion, i.e. feeding non-corn based grains, 2) ensuring testing procedures are in place at feed suppliers, especially in times corn supplies are short, lengthy storage times or following high moisture harvesting, and 3) feeding fresh, non-moldy grain and hay. There is no specific antidote for the toxin, therapy is primarily supportive.

Aflatoxins are toxic products produced by Aspergillus mold. It can be produced by mold in several feedstuffs, most commonly in stored cottonseeds, peanut meal and corn. The clinical signs are similar to ELEM. Treatment includes the same preventative measures, and again therapy is primarily supportive. OADDL provides testing for aflatoxins.

Ergot mycotoxin is produced by the Claviceps mold. Problems are most likely to occur during damp weather during plant flowering time. Horses are rarely affected by ergotism, but may show similar signs of other livestock: behavioral effects (hyperexcitability, aggression, ataxia, excess salivation, among others), swelling of extremities, reproductive problems (abortion, agalactia, etc.) and reduced feed intake and growth. Behavioral changes are the most commonly reported effect in horses.

Fescue Toxicosis
Fescue Toxicosis is caused by consumption of tall fescue infected with the fungus Acremonimum. It is commonly observed as reproductive problems in broodmares. Most of the fescue in Oklahoma contains the fungus. Treatment is primarily preventative by removal of bred mares prior to foaling, or administering preventative drug therapy. More details on this toxicosis is available in OSU Current Report-3917, Fescue Toxicity and Horses.

There are more than 300 chemically different mycotoxins with different sites of action, mechanisms of toxicity and effects. Problems are not frequent unless growing conditions or grain storage conditions promote mold growth. As such, most incidences appear as 'epidemics'. Usually, young animals are more susceptible and severely affected than older animals at similar levels of intake of mycotoxin, although ELEM has been reported to affect older horses moreso than young. Usually, cereal grains are the suspect, although mycotoxins can occur in hays and pasture forages as with fescue toxicosis. The OADDL is involved with supporting the veterinary community in testing and diagnostic procedures for many of these mycotoxins.

Best treatment is prevention, so remind horse owners of the need to provide clean, fresh sources of feed and to feed purchased grain within two weeks of delivery. Although problems can arise before visual mold growth is apparent, it helps to pay close attention to grain and hay sources so not to feed any suspicious-looking or moldy feeds and not feed untested sources of corn in times when aflatoxins or fusarium may be on the increase. Also, keep feedstuffs dry as most mold growth is promoted when feed is stored at high moisture levels (over 13 to 15%). If there is questionably behavior with horses, check feed sources for the potential of mycotoxin ingestion. Mycotoxicosis is not a frequent problem with the majority of horse owners because of selection and purchase of quality, fresh feedstuffs and good feeding management to reduce the incidence of mold growth in feeds.

Oklahoma Cooperative Extension Service
Division of Agricultural Sciences and Natural Resources
Oklahoma State University