Mycotoxins remain diagnostic problem for experts

Mycotoxins are naturally produced by moulds in the field and during storage of forages and grain.

There are a variety of compounds produced and as many as 500 different specific mycotoxins have been identified.

However, when veterinarians or producers submit feed for mycotoxin testing, the diagnostic laboratory usually tests for only a limited number of mycotoxins such as deoxynivanlenol (DON), zearalenone, T-2 toxin, fumonsin B, aflatoxins and ochratoxin A.

These compounds are primarily produced by the aspergillus, fusarium and penicillium moulds.

Corn, which has become a more popular grazing and silage crop on the Prairies, can be particularly affected by moulds such as aspergillus and fusarium.

Recent evidence suggests that a cow’s greatest exposure to mycotoxins may come from forages, such as hay and silage.

Last year’s weather during the forage growing season was favourable for mould growth and the formation of mycotoxins.

The toxicological laboratory at Prairie Diagnostic Services has identified many forage samples with very high levels of mycotoxins.

A variety of cattle health conditions, performance problems and diseases have been associated with the ingestion of mycotoxins.

Conditions such as feed refusal, reduced feed intake, reduced milk production, gastro-enteritis, reproductive effects, immune suppression and compromised rumen function have all been associated with various mycotoxins.

Limited scientific data exists to provide clear guidance on the levels of specific toxins that could be considered toxic in cattle.

There are reasons for this limited knowledge:

  • The mycotoxins rarely occur in isolation. There are often multiple compounds produced, and the interaction between various mycotoxins may be an important aspect of their toxicity. In some cases, the mycotoxins found in testing may merely be markers for other mycotoxins that can be detrimental.
  • The bacterial population and feed particles in the rumen are able to detoxify many myco-toxins, making cattle less susceptible than non-ruminants, such as swine and poultry. However, this detoxifying effect is limited and can be overcome. Young pre-ruminant calves with limited rumen function or cows with sub-optimal bacterial populations (cows with lower intake or inadequate nutrition) may be more susceptible to mycotoxins because of this. Mycotoxin effects may also be amplified by production stress and heavily lactating cattle. As well, rapidly growing cattle may be more susceptible. The effect of specific myco-toxins can vary depending on factors such as diet, immune status and production levels.

It is not unusual to find high levels of mycotoxin exposure in some herds with no apparent detrimental effects.

It is also easy to associate any disease event, such as abortions, with high mycotoxin levels when this may not be the actual cause.

This creates a problem for producers, veterinarians and nutritionists when trying to make decisions and recommendations about mycotoxin testing and acceptable levels in feed.

Mycotoxin testing of forages at Prairie Diagnostic Services can test for the common mycotoxins. It is important to send a representative sample by using a core sampler on multiple bales or by sampling multiple aspects of a grazing crop or silage pit.

High levels of mycotoxins along with the identification of a clinical syndrome that could be associated with mycotoxins, such as feed refusal, poor growth, abortions or estrogenic effects such as swollen vulvas and vaginal or rectal prolapses, may require changes to your feeding strategies.

Obviously, mouldy feed should be avoided if possible, but that may be difficult in some years. In such situations, you may want to blend the contaminated feed or feed it to a group of cattle that may be less susceptible to mycotoxins.

As well, improving the ration’s protein and energy may help offset some of the effects of mycotoxins.

There are organic and inorganic products that may help reduce the absorption of mycotoxins in the gut.

Inorganic products such as silicate minerals and activated charcoal can be added to a ration, but large quantities need to be consumed to be effective.

Organic products such as glucomannan polymers have a strong capacity for absorbing mycotoxins and have been used in dairy cow rations to minimize the toxic effects of mycotoxins.

The many variables, such as animal production levels, various diets and other environmental factors, make it difficult to provide definitive guidelines on acceptable mycotoxin levels in cattle feed.

However, it is especially important this year to be aware of the potential harmful effects of myco-toxins in forages and to make sure it is not causing a problem in your herd. You may want to consider working with your veterinarian or nutritionist to test your forages.

John Campbell is head of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.

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