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Mycotoxins in livestock feeds

Most mycotoxins are extremely potent and produce clinical disease at very low levels in contaminated feed

Proper nutrition is an important aspect of livestock production. In many instances, the emphasis is placed on vitamin, mineral, protein and energy content of the ration. With appropriate ration formulation, the producer can control these basic nutritional factors. Unfortunately, there are many aspects of livestock production that are not easily controlled.

Varying environmental conditions may have an impact on feed quality. For example, altered plant metabolism may result in the accumulation of toxic levels of nitrate or cyanide in the plant. During periods of high humidity and temperature, many moulds or fungi may grow in livestock feeds.

These moulds may adversely impact the protein, vitamin or energy content of the ration. Supplementation may be required. In addition to the reduced nutritional content of the feed, many of these moulds under the appropriate environmental conditions will produce a variety of highly toxic chemicals known collectively as mycotoxins. Mycotoxins are secondary fungal metabolites. Many different types of mycotoxins are reported worldwide. Since moisture and temperature conditions vary from region to region, the distribution of mycotoxins in animal feeds exhibits considerable geographic variation. In Canada, mycotoxin problems are considerably less common compared the many agricultural areas in the United States. Mycotoxin contamination of livestock feeds imported from the U. S. should be a concern for Canadian livestock producers.

In Canada, mycotoxin problems are encountered more frequently in Eastern Canada as compared to Western Canada, although, in some years, areas of Manitoba and Saskatchewan have encountered significant contamination of feeds with dioxynivalenol (vomitoxin or DON) and ergot, respectively, in localized areas. Most mycotoxins are extremely potent and produce clinical disease at very low levels in contaminated feed. This presents a problem in terms of chemical detection. The mould growth and potentially mycotoxin production do not occur in a uniform fashion in the feed. It is important to collect feed samples from several locations within the stored feed. Mycotoxin testing is not considered as a routine analysis in most laboratories. A specialized analytical laboratory will need to be identified. Since mycotoxins produce adverse effects in livestock at extremely low levels, analysis of blood or tissue samples from clinically affected livestock is generally not useful to confirm a diagnosis. Rapid metabolism and elimination of the mycotoxins from tissues also compromises tissue detection. From a food safety perspective, the rapid elimination of mycotoxins limits tissue accumulation and contamination of edible tissues. Once affected livestock have recovered, lengthy withdrawal times for consumption are not required.

Mycotoxins are usually found in grain. One notable exception is sweet clover poisoning (dicoumarol). This bleeding disorder is associated with the consumption of mouldy sweet clover hay or silage. It is important to note that the extent of mould in the feed is a poor indicator of mycotoxin content. Some grain samples with little visual evidence of mould may contain high levels of mycotoxin.

Culturing feed samples for type and amount of mould has limited application, diagnostically, to confirm a case of mycotoxin poisoning in livestock. In many instances, the clinical syndrome associated with each mycotoxin or mixtures of mycotoxins is often vague. The mycotoxins are not distributed uniformly in the feed and the low level exposure may be intermittent. The syndrome usually manifests as a herd problem. Depending upon the mycotoxin present in the feed, reduced growth, reproductive problems, abortion or an increased incidence of infectious disease such as pneumonia, may be observed. Within a herd, the clinical syndrome may be associated with the feed or a change of feed.

Mycotoxins are usually associated with stored feeds. The outbreaks are often seasonal and correlate with the time of year the stored feeds are consumed. Mycotoxin exposure is rarely associated with pasture grazing. Moist grain stored in bins may overheat. Heated grain may have reduced nutrient value, but it is unlikely to contain mycotoxins.

Mycotoxins affect specifiorgan systems to varying degrees. To fully charactierize the nature of this vague problem, consultation with your veterinarian is important. They will have a good appreciation for the specifimycotoxins found in your area. Feed analysis is critical to confirm cases of mycotoxin poisoning in livestock.

Dr. Barry Blakley is a veterinary toxicologist at the Western College of Veterinary Medicine at the University of Saskatchewan. Vet Advice is co-ordinated by the Western Canadian Association of Bovine Practitioners.

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