Problems with mycotoxins in dairy cattle are not always easy to recognise

Traditionally, there are the so-called “big 6” mycotoxins (Aflatoxins, Zearalenone (ZEA), deoxynivalenol (DON), T-2 toxin, Fumonsins and Ochratoxin A (OTA)), sometimes also referred to as "AFOZET mycotoxins", that are associated with several mycotoxin problems in dairy cows. More recently, new groups of mycotoxins, the so-called silage mycotoxins have been identified[108,109,110]. Lastly, there are the Endophytes, moulds that grow inside plants and can cause problems in gazing dairy cows. These silage mycotoxins and Endophytes can be different from the “big 6” mycotoxins and hence understanding the presence and negative effects of these silage mycotoxins and endophytes in dairy cows is very important.

Where do mycotoxins come from and what problems can they cause in dairy cattle?

Table 1 shows which feed ingredients can contain the various AFOZET mycotoxins of dairy cattle and what the effects of mycotoxins in dairy cows can be.

Table 1: Feed sources of important mycotoxins of dairy cows and their effect on health, performance, and reproduction.

The risk of mycotoxins is much bigger in dairy cows than in monogastric animals because the chances of exposure to mycotoxins through various ingredients is much higher (see Figure 1). There is no doubt that microbes in the rumen of the cows, particularly protozoa, can help to lower mycotoxin toxicity, particularly in case of a challenge with ochratoxin A (OTA). Some mycotoxins can however have a negative effect on the ability of rumen flora to detoxify mycotoxins. Next to that, modern dairy cows do have an increased passage rate of feed through the rumen, leaving less time for microorganisms to detoxify. In case of sub-acute ruminal acidosis (SARA), the number of protozoa in the rumen declines, having a negative effect on the ability to detoxify mycotoxins. As a result, the awareness of farmers, nutritionists, and veterinarians that mycotoxins indeed are a significant challenge to dairy cows is increasing.

The alternative to measuring mycotoxin levels in feed with expensive tests is mould analysis. Depending on the extent of information needed, further identification of mould species is possible in some commercial labs. Such identification helps in understanding whether the mould identified can produce mycotoxins and if yes, which types of mycotoxins potentially can be present (see Table 2).

Table 2: Moulds and mycotoxin relationship. Mycotoxins produced by Penicillium species in silages are highly volatile and hard to analyze by conventional methods.


Because there is no cheap and practical way to measure the levels of mycotoxins in a TMR or high-fibre feed ingredient for dairy cows, the alternative is to combine two methods. Ingredients with a low amount of fibre should be analysed for mycotoxins using a rapid mycotoxin test such as the Mycomaster, whereas mould analysis should be used to assess mycotoxin risk of the total TMR or ingredients with high fibre content (see Table 3).

Lastly, there is the option to test feacal samples of dairy cows for moulds. This method is not very accurate, as the presence of moulds only indicates there has been a problem in the recent past and also, it does not provide any information as to where the mycotoxin contamination is coming from, but is is a simple method that can be used to find out if a mycotoxin problem is a likely or unlikely cause of problems with health, performance and fertility in a dairy herd.

Table 3: Diagnostic tools for understanding total mycotoxin risk in ruminants

What are the tolerance levels for moulds and mycotoxins in dairy cattle?

Based on the combined knowledge of both peer-reviewed research and field experience, Trouw Nutrition has developed “Practical Mycotoxin and Mould Guidance Values” (see Table 4). These values should be considered as a guide to manage raw material and TMR quality, ultimately protecting animal performance and bottom line of operations.

Table 4: Mycotoxin and mould guidance values for TMR for dairy cows. Aflatoxins recommendations are based on FDA regulation and the values are much lower for EFSA regulation.

Irrespective of the source and the type of mycotoxins, overall health, performance, and reproduction of dairy cows are significantly affected by poor quality raw materials and TMR. This impact has increased in recent times as rumen health and the immune system of high yielding dairy cows is relatively compromised. The risk of mycotoxin exposure is much higher in dairy cows as compared to monogastric animals and hence an integrated approach should be in place when procuring raw materials, producing feed and silages, and rearing dairy cows. In terms of milk quality, aflatoxin M1 residues in milk is a global concern and that requires HACCP-like approach as the problem ends in compromising human health.