Measures available to protect equine from fescue toxicosis

With summer just around the corner, thoughts of another season of drought and in turn the increased presence of mycotoxins are crossing many equine owners' minds.

"The global climate change has resulted in climatic extremes which are increasing the frequency of mycotoxin contamination of cereal grains, forages and silages," said Trevor Smith, animal science specialist at the University of Guelph.

Plants stressed by drought and high temperatures are commonly invaded by mold spores which can produce mycotoxins. Mycotoxins are harmful compounds produced by molds that are found in the soil and can grow on vegetable matter including grain, forages and silages. Mycotoxins can be formed in the field preharvest and may continue to be formed under suboptimal storage conditions postharvest. One of the best-known mycotoxins is the one produced by endophyte-infected fescue grass.

Tall fescue is one of the most important cool-season grasses in the U.S. and has become a valuable grassland resource due to its extended grazing season, pest resistance and tolerance to grazing pressure. But the grassland source also has its shortcomings.

Toxins produced by the endophytic fungus grow symbiotically on tall fescue and have a wide range of health implications for horses and pregnant mares. The impact of fescue toxins on performance and reproduction of equine include rough hair coat, prolonged gestation, dystocia or thickened placenta, late term abortions, neonatal death, decreased prolactin and progesterone, poor conception rates and agalactia or low/no milk production.

"These toxins can reduce performance of horses by altering both their metabolism and behavior," Smith said.

"Reduced feed intake and subsequent reductions in performance are commonly seen when feeds are contaminated with mycotoxins."

A faculty member for more than 30 years at Guelph, Smith has devoted much of his research to the characterization and dietary treatment of mycotoxicoses. While mycotoxins are nothing new to the animal feed industry, the research on toxins has greatly expanded. Once thought of as individual toxins, scientists have now determined that mycotoxins can form compounds and increase toxin responses in livestock.

During his research of mycotoxins, Smith has worked on finding a number of solutions to the exceeding problems of toxins in animal feed. One of the first steps Smith takes is examining materials for high moisture. In this case, he suggests the use of a mold inhibitor. A mold inhibitor can be applied to lower the pH so that molds will not grow and produce more toxins. But as Smith noted, the product is only really useful if the material is unstable and high moisture because it will only keep it from getting worse by killing the mold spores.

Speciality enzymes are another approach to mycotoxins in feed. When a source of enzymes is added to feed, the toxins are degraded and broken down in the intestinal tract; they then do not enter the blood. While a number of enzymes are on the market, Smith pointed out the problem with the enzyme approach is that it is most suitable if there is only one toxin, such as alfatoxin because the enzymes are very specific.

The last strategy Smith advises is the use of a suitable mycotoxin adsorbent. There are two types of adsorbents -- silica-based polymers and carbon-based digestible fibers. Silica-type materials are readily available and many have shown to be effective against aflatoxins and also Fusarium toxins.

"The challenge with the clay materials is that they are required to be in the feed at a very high level of inclusion," Smith said. "The advantage of the clay materials is the low price. If you put it in at a high level, you lose the price advantage. If you don't put it in at a high level, the silica clay materials tend to be ineffective."

The other alternative is carbon polymers or plant fibers. An example of one that Smith and other researchers at University of Guelph found that worked well against Fusarium toxins, including zearalenone and T2 toxins was the fiber from alfalfa. While the fiber worked well, it too had to be added at a high inclusion level. Smith said they also found that some of the fibrous plant materials like alfalfa can be contaminated with Fusarium toxins as well.

An organic polymer from Alltech, a glucomannan polymer extracted from the cell wall of the yeast, is a natural fiber source. Smith said the advantage of the yeast material is that it has a very high surface area so practical levels of inclusions can be incorporated.

"The only complete solution to the problems arising from mycotoxins in equine feeds is to avoid the feeding of mycotoxins-contaminated feedstuffs," Smith said. "But adverse climatic conditions are, however, beyond our control so even if feed grains can be monitored by strict quality control, forages cannot."