Dairy Nutrition: Mycotoxins and Binders

About 20 years ago, the animal feed industry began to notice the prevalence of mycotoxins in many of the feedstuffs fed to dairy and beef cows. The word mycotoxin literally means “fungus-poison.” Mycotoxins are produced naturally by molds and fungi in fields and during the storage of grains, feeds and forages.

As far back as the 1960s, a group of mycotoxins called aflatoxins was identified as being a significant health risk to humans. However, many other mycotoxins have the potential to harm humans and animals. Of all the known mycotoxins, aflatoxins are currently the only ones regulated by the FDA, with maximum amounts allowable in food for humans and animals.

Mycotoxins can be considered soilborne pathogens, since they originate in crops such as grains and forages. Dairy and beef cow diets generally include both grains and forages, which increases the risk of exposure to mycotoxins. Forages, fermented feeds and byproducts can represent a significant risk depending on soil contamination, forage harvesting date, silage management and storage conditions.

The concern over mycotoxin contamination in animal feeds is growing due to a combination of factors:

  • Changes in the climate and agronomic practices have created environments more suitable for mold growth.
  • The volume of grains traded globally has increased, thus increasing the potential for contamination.
  • Higher-producing dairy cows are more susceptible to the effects of mycotoxins.

The fungi and molds associated with mycotoxins fall into three broad groups:

  1. Penicillium
  2. Aspergillus
  3. Fusarium

Hundreds of mycotoxins have been identified, and they’re usually associated with diseased and moldy crops, as well as growing conditions that encourage the growth of molds. The most commonly analyzed mycotoxins include deoxynivalenol (DON/vomitoxin), zearalenone, T-2 toxin, fumonisin B1, aflatoxins and ochratoxin A.

Mycotoxins seldom occur in isolation. Given the fact that one mold is capable of producing several mycotoxins, several molds can contaminate one feed ingredient. With several ingredients included in a ration, it’s not uncommon to find multiple mycotoxins in finished feeds. This allows for interactions among mycotoxins, resulting in synergistic or additive effects on the animal. Mycotoxin interactions result in unexpected animal toxicity and make diagnosis difficult.

Ruminants are exposed to mycotoxins in a variety of ways, including grazing pasture (fungal contamination of grasses); feed or total mixed ration (TMR) made with contaminated ingredients; and moldy silages.


Mycotoxins found in animal feeds have the potential to severely impact the economic well-being of a dairy farm through forage loss or reduced crop value, reduced milk production, milk or meat discards due to risk of contamination in the food chain, increased mortality rates, increased vaccination costs and reproductive losses.

Mycotoxins are found in nearly all forages and processed grains. Eliminating them from the environment is nearly impossible. Crop and dairy farmers will find that the level of mycotoxin contamination in feeds varies from year to year and from different growing conditions. Since the majority of feed grown and stored on dairy farms is forages – corn silage and hay crops – dairy farmers must be aware of the conditions that are conducive to the occurrence of mycotoxins in forages.

Fungicides have been found to have little effect on reducing or eliminating mycotoxins in forages. The best agronomic practice for controlling mycotoxins in forages is crop rotation. Monocultures, or the planting of closely related crops one after the other on the same field year after year, will enhance the risk of mycotoxin formation. Spores will transfer to the subsequent crop and thus allow fungal growth. Plowing under harvest residues will reduce spore contamination of the subsequent crop and thus reduce fungal infestation and mycotoxin formation. No-till systems seem to enhance the risk of mycotoxin formation in a field. Crop varieties that are more resistant to foliar fungal diseases reduce infection and thus mycotoxin formation in the crop.

Mycotoxin binders and absorbents added to cows’ diets have been around for many years. These products react with mycotoxins in the cow’s digestive system to render them ineffective or less effective. Binders come in two forms, inorganic or organic.

Inorganic binders are essentially clay (from soil) products consisting of a variety of chemical elements that react or bind with the mycotoxin molecules. Not all inorganic products work on all mycotoxins. Such materials are often inexpensive and easy to handle. These products are traditionally mixed with finished feeds at a mill or mixed on-farm in mixers. Costs are low, but they require a high inclusion rate.

Organic binders are essentially carbon-based polymers – carbohydrates. Examples would include products such as oat hulls, wheat bran, cellulose, pectins and yeast cell walls. Again, each of these binders can react with toxin molecules, making them ineffective in the digestive system.

In recent years, there has been much research conducted on yeast cell walls. Different strains of yeast have varying levels of cellulose and sugars, known as mannan-oligosaccharide (MOS). These molecules can and do bind with different mycotoxins. Advanced research is being conducted on MOS products to identify binding sites that will interact specifically with a selected mycotoxin.

Dairy and beef farmers who feed fermented forages and/or pasture their cattle would benefit by adding mycotoxin binder products that contain both an inorganic and an organic mycotoxin binder. We know that some level of mycotoxins can be found in most feeds, no matter how careful a farmer is in growing and storing them. Mycotoxin binders are sensible insurance that will help control the problems associated with mycotoxins when the need arises.