During the past few months, we have seen several herds with diarrhea, unusual digestive upsets and unexpected deaths. In some herds, additional symptoms have included abortions, decreased milk production or feed refusal. In all cases, the culprit has been mycotoxin-contaminated feed — most generally, corn grain.

What they are
Mycotoxins are the toxic metabolites that are produced by molds. 

Some evidence suggests that mycotoxins may persist in the field — particularly in no-till farming systems — thereby contaminating new plants as they emerge. Fusarium mold spores, in particular, are believed to enter the plant at germination.

A wide variety of mycotoxins can be found in grains and feedstuffs. And contrary to popular belief, they are not inactivated during storage or ensiling. Some of the more common ones are:

  • Aflatoxins, which are produced by Aspergillus sp.
  • T-2 toxin, vomitoxin, zearalenone, and other fumonisins, which are produced by Fusarium sp.

In general, the aflatoxins tend to be produced by mold growth during hot weather, while mycotoxins produced by Fusarium sp. tend to be produced during cooler temperatures. In the Midwest, wet weather during harvest often leads to mycotoxins. Plant damage from hail, insects or drought also favors their production.

Their effects
Once consumed, most mycotoxins will inhibit protein synthesis. Exactly how they affect an animal is determined by which organ or system is most affected by the reduction in protein synthesis at that time. Areas most commonly affected include the liver, the intestine, the immune system, or all of the above. 

Clients often want to know the minimum safe level of mycotoxins they can feed. The problem is, most feed samples contain more than one type of mycotoxin and their actions tend to be additive and synergistic. Therefore, determining a “safe” level for mycotoxins is difficult. Instead, I regard any detectable presence of mycotoxins as a problem if it is coupled with the presence of unexplained diarrhea, liver or kidney problems or general immune suppression in a herd. 

We use a thin-layer chromatography test on forages and an ELISA test on grains, and generally request a mycotoxin-screening test that will check for several different toxins.

Rules to live by
How can you avoid mycotoxin problems?  Don’t feed moldy feeds. Granted, not all moldy feed has excessive concentrations of mycotoxin. But mold growth does reduce the nutrient content, digestibility and feed value of the feed.

If feed containing mycotoxins must be fed, we recommend two concurrent strategies: (1) dilute it or feed as little as possible and (2) use a feed additive that will help inactivate the mycotoxin.

One class of feed additives is a binding agent, such as clay or bentonite. These products have worked specifically with aflatoxin. However, the probability that these binding agents will bind any or all of the mycotoxins in a batch of feed can be limited, and they are not always effective in the field.

In my experience, organic compounds (oligosaccharides) have been more effective as binding agents in the field. In addition, direct-fed microbial products that specifically metabolize and inactivate certain mycotoxins are now available as feed additives. These microbial products also have a direct stimulatory effect on the immune system that may aid in field situations as well. (The mechanism of this immune stimulation is unknown.)

Try to avoid mycotoxin-contaminated feed. If some contaminated feed must be fed, use it sparingly and use an additive to help neutralize its effects.

Don’t overlook it as a cause of unexplained herd-health problems.

Brian J. Gerloff is a veterinarian and operates Seneca Bovine Service in Marengo, Ill.