Mycotoxins. Reducing poisons in your feeding systems

Dairy Pipeline: May 2005

Andy Overbay
Extension Area Dairy Agent,
Southwestern Virginia
(276) 223-6040 email: aoverbay@vt.edu

If you were asked what level of poison you are currently feeding your cows, you'd probably take offense-and rightly so. However, in some instances, poisons may be being delivered to your animals without your knowledge. The culprits for this hidden danger are Mycotoxins. Mycotoxins are difficult to treat because they are constituted by a wide variety of organisms (mostly fungi and molds) and their resulting poisons, each having a different mode of action on the host organism. Even the species of the animal itself makes a difference in the danger of Mycotoxins. Horses and swine are most susceptible to the ravages of mycotoxins. However, poultry and ruminants are not immune to their effects. At present, the only known ways to combat mycotoxins are by complete removal of the infected feed source or by feeding binding agents mixed in the animals feed. It is proposed that horses and swine are least likely to be successfully treated by binding agents because their rate of feed passage does not allow the agent to "catch up" with the offending toxins. Dr. Peter Spring of the SHL Institute in Bern recently spoke on the subject of mycotoxins at a meeting of feed industry personnel in Wytheville. According to Dr. Spring, the most commonly known mycotoxins are Alfatoxins which are carcinogenic and affect liver function and Fusarium, a wide ranging family of organisms that decrease milk and reproductive efficiencies. One of these poisons, Fumonisin (B1) is a linear chemical that damages the cell membrane. The "leaking" tissues cause edema that causes increased pressure on areas like the brain. Deoxynivalenol (DON) affects the animal by inhibiting protein synthesis, which leads to increased free amino acids in the blood. This in turn affects the kidneys and also appetite by decreasing serotonin levels in brain tissues. We usually think of mycotoxins being carried by grains and indeed when we have high yielding corn grain years (like this past corn year), it seems that mycotoxin pressures increase. Of tested feeds, whole grains (like whole wheat with the bran still in place) have infection rates higher than any other feed source. This means that most of the feed grains that we grow on the farm are sources of mycotoxins. It would be incorrect to think that the threat is diminished if you do not grow or feed grain. Zearolenone (ZEA) affects pastures and can affect cows and lambs dramatically at levels as low as 3 parts per million. In fact at that level, live lambing will be reduced by 15-50%! Levels of 500 parts per billion as tested by Dr. Lon Whitlow of NC State exhibited the ability to reduce pregnancy rates in dairy heifers by 30%. Heifers with ZEA poisoning will exhibit estrogenic effects, like swollen udders prior to breeding and estrus expression during pregnancy. ZEA is usually found only in sparse areas in the pasture. The only true way to measure ZEA pressures are to collect urine samples from the animals that are harvesting the pasture. ZEA is found mostly on the unused undergrowth that overwinters in the pasture. Corn crops can be adversely affected by ZEA and DON. As in the pasture, these mycotoxins exist mostly in residues from past crops. In Europe, plowing residues under dropped mycotoxin pressures from an average of 6.1 to 1.8 ppm. While this might not be an option according to your tillage protocols, it has been shown that assisting the breakdown of the residue (such as bush-hogging or shredding the corn stubble) has much the same affect on mycotoxin levels. European studies also show that certain varieties of corn are more likely to grow mycotoxins. While studies are inconclusive, Dr. Spring does feel that varieties that stay green longer seem to have higher mycotoxin levels. In conclusion, some strategies for reducing mycotoxin pressures in your herd are to manage crop and pasture residues and manage the storage of your crops and control (or prohibit) additional moisture (rain). Also you can dilute infected grain with clean grain sources, divert the feeds to less susceptible species or add proprionic acid to the feed during harvest.

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