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Mycotoxins and MicroNutrients

  

By: Dr. John Doerr, Ph.D., PAS, Dpl. ACAP 

I want to return to an issue from a few years ago about DON in dairy cows and the influence on vitamins and minerals it has.  There are many mycotoxin-related circumstances that have effects.  Aflatoxin and others cause various malabsorption syndromes.  E.g., fat soluble vitamins (A, E, D, and K) cannot be absorbed as expected, and perhaps, very poorly.  Interactions with other toxins may add to this. Mycotoxin-induced metabolic problems affect vitamin use. For example, the major target organ of ochratoxin and citrinin is the kidney.  One function of the kidney is the conversion of cholecalciferol (basic vitamin D) to 24,25-dihydroxy cholecalciferol, the bioactive form of the vitamin.  The activated vitamin is needed for uptake of calcium from the intestine. This is key in animals that draw from bone reserves to supply high calcium requirements for milk and eggshells. Then, there is suppression of protein synthesis by most mycotoxins.  Go back to the calcium uptake issue...a second key part of this system is a carrier protein, calmodulin, which must be active for calcium transport to occur. Reduce calmodulin and calcium uptake will be impaired. And this list can go on and on. 

Vitamin supplementation is generally not effective at ameliorating mycotoxicoses. But (there is always a "but") vitamin E is tied in with the actions of selenium on toxin by the liver. If this is impaired, conversion of primary toxin metabolites to water soluble forms for excretion is also impaired yielding increased the impact on the cow.  Vitamin supplements may help in malabsorption. A smaller percentage of total vitamin is absorbed, but a larger amount in the digesta yields about the same total absorbed vitamin.

Add to the overall risk the times when dairy ration balancers, because milk markets are low and feed costs high, push the ration formula to the absolute bare bones to conserve dollars.  The usual excess of vitamins and minerals is now fine-tuned to absolute minimum requirements. That's perfectly fine if all else is well, but if oxidation has reduced vitamin activity or mycotoxins reduced absorption, what on paper as adequate may now be below that threshold.  

In the real world, herds showing apparent deficits of vitamins or minerals may be getting more than adequate in the diet and need more attention to factors impacting use of those micronutrients.  And, if an appropriate feed additive reverses the situation, even if a particular mycotoxin report is low or negative, that just goes to show that the few toxins we test for are not the only fungal toxin players on the farm.  In the real world, it is unusual for a dairy cow to read a nutrition textbook and follow the theoretical rules: each animal varies in its personal requirement for specific micronutrients, and each varies in its response to particular toxins at particular levels.  Finally, dairy nutritionists are pretty savvy when it comes to knowing what the cow needs to eat at particular phases of her life cycle, and how to put together the right combination of ingredients to get those requirements met.  

But once in a while, even the best of us needs a little nudge to remind us of both the complexity of the metabolic cycles that all must work in harmony and also the absolute daily need to be vigilant for the more than 2,000 possible mycotoxins that can be influencing those cycles. 

How can the dairy farmer avoid mycotoxin-related issues with vitamins and minerals?  Just ask your Select Sires or Agrarian Solutions representative!