Challenges in the diagnosis of mycotoxicosis in dairy cows

Dr. Haladi discussed the complexities posed by masked and emerging mycotoxins, as well as the specific risks that must be mitigated at every stage of feed production – from raw crops in the field through harvest, storage, transport and processing. Dr. Haladi explained why mitigation strategies must go beyond conventional binding approaches and how a multi-pronged strategy can leverage multiple mechanisms to manage and mitigate mycotoxin issues in dairy cattle.

This year, there has been widespread drought damage to corn in Europe leading to a 15-year low production. As a result, a four-year high EU maize import is expected. Aflatoxins can be a challenge during drought years. Next to that, there is an RASFF alert suggesting that moulds are entering European market through ingredients (via sunflower meal and wheat bran). The Ukraine exports 42% of the worlds export of sunflower oil, 16% of maize, 10% of barley and 9% of wheat. The war in the Ukraine caused 30 million tons shortage of food across Africa and a 40% rise in food prices. Exports from Russia also declined.

On the other hand, corn exports from Brazil are forecasted at 46.5 million tons 2022-23, up 2 million tons from 2021-22, due to the expectation of a record harvest and high international demand. 80% of Brazilian corn is produced during the winter months and therefore, Fusarium mycotoxins will be prevalent.

There are a lot of different reasons that diagnosing a mycotoxicosis problem in dairy cattle is difficult:

• There are a lot of different dairy feed ingredients that can be a potential source of mycotoxins for dairy cattle
• Rapid test methods for mycotoxins are not satisfactory for high fibre materials
• Silage mycotoxins of dairy cows are commonly present in dairy feed ingredients but are difficult to analyze
• Ergot toxins of dairy cattle are highly sensitive
• Mycotoxin myths are very common in dairy cow farming
• The use of low-quality raw materials in dairy feed is common
• Oxidative stress is a major issue in dairy cows

Sampling errors further complicate the diagnostic process. Procedures used to take a sample from a bulk lot are extremely important. Every individual item in the lot should have an equal chance of being chosen. Examples of a sampling bias are:

• Use of sampling probe that does not allow larger particles into the probe
• A probe that does not reach every location in the shipment
• Use of a single probing point in a poorly mixed plot
• 200 g incremental portion for every 200 kg of product

Newly emerging mycotoxins are neither routinely analyzed, nor legislatively regulated; however, the evidence of their incidence is rapidly increasing¹ (see Table 1).

The role of masked mycotoxins in dairy cattle

Masked mycotoxins are conjugates of DON, ZEA, OTA reported in corn, wheat and barley. They are masked to detection methods, but still biologically active and bioavailable in digestive tract by enzymatic activity. There prevalence is estimated to be between 9 and 88%².

Specific and non-specific effects of mycotoxins in dairy cattle

There are specific effects of certain mycotoxins in dairy cattle such as:

• Skin problems
• Reduced fertility
• Abortions
• Excretion of aflatoxin M1 in milk

Non-specific effects of mycotoxins in dairy cows are much more common. The following non-specific effects of mycotoxins in dairy cattle can be observed:

• Reduced feed intake
• Reduced milk yield
• Poor milk quality
• Lameness
• Rumen acidosis
• Increased somatic cell counts
• Mastitis

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. There are two ways to measure mycotoxin levels in dairy feed. There are rapid tests that can be used on site and there are tests that need to be carried out in the laboratory. Next to that, there is an indirect method to assess the risk of mycotoxin contamination through mould analysis. Rapid mycotoxin analysis is recommended for raw materials having less than 15% moisture and low fiber content. Laboratory methods or mould analysis is recommended for raw materials or TMR with more than 15% moisture and high fiber content.

Laboratory methods

Both HPLC and LC-MS/MS methods can be used to measure mycotoxins in TMR and high-fiber ingredients. These methods are not practical due to the time consumed to obtain results as well as the high cost per sample analysis and are thus mainly used for research purposes.

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 or ingredients with a high moisture content. The Mycomaster+ can analyze AF, DON, FUM, ZEA, T2/HT-2 and OTA mycotoxins in raw materials and feeds in raw and AFM1 in Milk. The Mycomaster + MRL is capable of detecting AFM1 at EU MRL (European Union Maximum Residue Limit) of 0.05ppb or 50ppt. The Mycomaster + SL is capable of detecting AFM1 at US-SL (United Sates Safe Level) of 0.5ppb or 500ppt.

Mould analysis of dairy feed ingredients and TMR

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.

Reducing exposure of ruminants 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. A robust mycotoxin risk management programme for dairy cattle should include a number of elements.

Reduce growth of moulds while crops are on the field

When crops are being produced, use high quality seeds only, ensure crop rotation and manage crop residues on the field. Reduce the future impact of mycotoxins at harvesting Apply correct harvesting procedures and if necessary, remove high moisture parts of plants. Add mould inhibitors and silage inoculants while making the silage.

Reduce growth of moulds during storage

Most mycotoxins of dairy cattle are chemically stable during storage. Therefore, reduce the growth of moulds as much as possible. Ensure silos are properly cleaned before crops or silages are stored. Optimise storage conditions, so reduce the level of moisture and ensure humidity control. In case of grass or corn silage, ensure the silage is properly closed. Identify which ingredients of the ration carry a risk and avoid feeding these ingredients if possible
No ruminant feed is entirely free from mycotoxin contamination and multi-contamination is very common. Test ingredients and avoid those that have mycotoxin levels above tolerance level. An alternative is to test the TMR and work backwards to identify high-risk ingredients.

Spray liquid mould inhibitors to the face of the silage after cutting

Moulds need oxygen, so they will start growing once a silage is opened. Therefore, inhibit the growth of moulds at the cutting edge of the silage once it has been opened by spraying a mould inhibitor on the surface of the cutting edge.

Add mycotoxin mitigation products for dairy cattle into TMR directly or through concentrate portion

A high-quality mycotoxin mitigation product should do a number of things:

1. It should bind mycotoxins and LPS. A good mycotoxin mitigation product for dairy cows should have a binding capacity for mycotoxins of at least 90%. At the same time, it should not bind amino acids and only have a limited impact on vitamin and mineral levels of feed. LPS increases gut permeability and reduces the elimination rate of mycotoxins, thus increasing exposure of the animal to mycotoxins.
2. It should reduce the risk of “leaky gut” in dairy cows. Mycotoxins can damage the tight junctions between gut cells, thus increasing the risk that toxins and pathogens leak into the circulation (“leaky gut”). A good mycotoxin mitigation product should therefore reduce the amount of damage to the tight junctions.
3. It should mitigate the negative effects of mycotoxins on the immune system. A good mycotoxin mitigation product should mitigate immunosuppression by increasing macrophage activity.
4. It should provide anti-oxidative support. Mycotoxins can be detoxified by liver. During detoxification, cell homeostasis is damaged, inducing the overproduction of free radicals, leading to oxidative stress in dairy cows. A good mycotoxin mitigation product should therefore reduce oxidative stress.

• The current global raw material situation pushes the dairy industry to use relatively poor-quality raw materials.
• Dairy cows are exposed to greater variety of mycotoxins as compared to other species of animals.
• Milk aflatoxin M1 management is of public health importance.
• Rumen health, intestinal health, immunity and anti-oxidant status in dairy cows can be compromised by multiple mycotoxins.
• Mycotoxin risk management strategies combining a mycotoxin binding concept along with means of improving gut health, immunity and anti-oxidant status are of paramount importance in not only enhancing health and performance of dairy cattle but also improving the bottom line of dairy farm operations.