Nutritionist > Equine

Co-contamination and further mycotoxins
Contaminated feeds or ingredients typically contain more than one known and probably several unknown mycotoxins. The toxic responses and clinical signs observed in horses when more than one mycotoxin is present in feed are complex and diverse.

Co-contamination of mycotoxins appears to exert greater negative effects on health and performance than do single mycotoxins. For this reason, symptoms typical of mycotoxicosis are often seen in horses despite analyses of the feed indicating only very low or zero concentrations of individual mycotoxins. Toxicity may be due to interactions between different mycotoxins that exaggerate the toxicity symptoms.

With mycotoxins the risk directly depends on the amount of major mycotoxins in the feed, the existence and level of other mycotoxins as well as age and health status of the horse. Therefore strictly speaking it is not possible to fully define safe levels of mycotoxins. This complex situation makes it critical to take the necessary precautions. The following table gives guidelines only.

Maximum Tolerance Levels of Mycotoxins in the Total Ration Dry Matter for Horses

Sampling and testing for mycotoxins
If clinical signs of mycotoxicosis are observed, it is important to properly collect a grain or feed sample and send it to a laboratory to determine the presence and level of the suspected mycotoxin(s). Sampling accounts for 80 - 90% of the error associated with measuring mycotoxins in grain or feed. Analytical tests for mould spore counts are of little or no value.

As mycotoxins are not evenly distributed throughout a batch of grain or feed, random samples (10 to 30) should be collected from several locations within a batch and combined thoroughly to provide a composite sample for submission. Using a grain probe at several evenly distributed locations will provide the most representative sample.

Samples can also be collected periodically from grain being augured which can also be an effective form of sampling. Paper bags should be used to transport sample(s), since plastic bags retain moisture, and therefore can promote additional fungal growth.

Contact the laboratory for specific sampling requirements prior to submission.

It is important to remember that based on the uncertainties associates with any mycotoxin test procedure, it is difficult to determine the true concentration of a bulk lot.

Mycotoxins are difficult to measure for a number of reasons:

• Many different mycotoxins can be present simultaneously, making analysis difficult and expensive.
• Sampling of bulk feeds is difficult. Mycotoxins are present in 'hot' spots and are not evenly distributed throughout the feed. Therefore strict sampling procedures should be followed with many samples taken from a particular batch to get a realistic reading
• It is only possible to analyse for certain, indicator mycotoxins and a negative result does not guarantee that no mycotoxins are present
• Mycotoxins can be masked – this basically means that the mycotoxin is conjugated to another molecule such as glucose. Whilst maskd mycotoxins are still toxic to the horse or animal, conventional methods of analysis cannot detect them meaning that mycotoxin levels can be underestimated.

Latest research has identified complexes of mycotoxins and their metabolites for which there is no accurate analysis method.