Assessing mycotoxin risk in dairy feeds has always been challenging. Most cases dairy cows are fed with Total Mixed Ration (TMR) containing silages, grains, and by-products. Although mycotoxins in TMR and high-fiber ingredients can be analysed, test methods are costly and not practical for routine analysis. On the other hand, more practical and affordable tests, such as ELISA and Lateral Flow Devices, are not particularly suitable for testing high-fiber ingredients. This problem can be solved by combining rapid tests that are practical for testing mycotoxins in ingredients with low amounts of fiber with mould counts and mycotoxin analysis for ingredients with high levels of fiber and for TMR.

Making a correct assessment of the risk of contamination with mycotoxins in combination with understanding the consequences of their presence and negative effective effects in dairy cows is very important to prevent problems with health, performance and fertility of dairy cows and problems with residues of aflatoxins in milk.

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.

Aflatoxins are mainly associated with feed safety issues

Aflatoxins can cause problems with health fertility and performance of dairy cows at high concentrations, but as they are very toxic for humans, tolerance levels in milk are relatively low. Aflatoxins in dairy cows are mainly related to problems with rejection of milk due to concerns about safety for human consumption. Thus, if there is an aflatoxin risk, particularly aflatoxin M1, a Hazard Analysis Critical Control Points (HACCP) approach will be required.

Mycotoxins cause problems with health, performance, and fertility of dairy cows

The symptoms caused by mycotoxins are mainly related to poor rumen fermentation, systemic immune activiation leading to poor immunity, hormonal imbalance and sometimes liver and kidney toxicity, all leading to poor health, performance and reproduction. There are many other causes for these types of problems, as a result, recognising a problem with mycotoxins isn’t always easy.

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.

How to assess the risk of problems with mycotoxins in dairy cows?

Compared to poultry and pigs, it has always been difficult to assess mycotoxin risk in dairy feeds. Most dairy cows are fed a Total Mixed Ration (TMR) containing forages, grains (including high moisture grains), protein meals, by-products and sometimes green grass or hay. Two methods to measure mycotoxin levels in feed exist. Next to that, the risk of mycotoxin contamination can be indirectly assessed by mould analysis of high moisture ingredients and TMR. Out of the 2 methods available for mycotoxin analysis, rapid mycotoxin analysis is recommended for raw materials having less than 15% moisture and low fiber content. Mould analysis is recommended for raw materials or TMR with more than 15% moisture and high fiber content.

HPLC and LC-MS/MS methods

Both HPLC and LC-MS/MS methods can be used to measure mycotoxins in TMR and high-fiber ingredients, but these methods are not practical due to the time consumed to obtain results as well as the high cost per sample analysis.

Rapid mycotoxin tests

Rapid mycotoxin tests, such as ELISA and Lateral Flow Devices (including Mycomaster), are excellent for testing important mycotoxins rapidly and at an affordable cost. Unfortunately, these tests are not particularly suitable for testing high-fiber ingredients.

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.

Reducing animal exposure to mycotoxins in feed is key. Identifying contamination can help to reduce exposure. Moulds can already grow and produce toxins when the crops are still on the field. High humidity, temperature and un-seasonal rains during crop growth and harvesting can increase mould prevalence and mycotoxin risk in dairy feed ingredients. Contamination and growth can however also occur during storage.

Robust mycotoxin risk management programme should comprise many actions, including:

• Identify which ingredients of the ration carry a risk
• Avoid feeding these ingredients if possible
• Reduce growth of moulds while crops are on the field or in storage
• Add mould inhibitors and silage inoculants while making the silage
• Spray liquid mould inhibitors to the face of the silage after cutting
• Add mycotoxin mitigation products into TMR directly or through concentrate portion
  
  

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.