Through years of exposure, ruminant cattle have evolved to be able to tolerate higher levels of mycotoxins in the diet when compared to their monogastric counterparts. However, the high demands placed on the modern dairy cow mean any slight impact on her ability to intake feed, absorb nutrients or reproduce is going to have a significant impact on the producer’s bottom line.

Ruminant diets commonly include both ensiled forages and grains; this combination increases the likelihood of a mycotoxin challenge when compared to animals who primarily consume grains or concentrates.

This variety of feeds opens up the possibility for a wide range of toxic encounters. Table 1 goes through a list of commonly found mycotoxins and the respected symptoms exposed when encountering a toxin overload.

mycotoxinsThrough proper ensiling techniques, the oxygen deprivation and the production of lactic and acetic acid during fermentation create an antibacterial and antifungal environment that prevents the growth of harmful fungi and therefore helps to limit mycotoxin contamination.

How does this happen?

Mycotoxins are secondary metabolites of fungi, which can contaminate animal feedstuffs both pre- and post-harvest. Globally, Aspergillus, Fusarium and Penicillium are the three most significant toxigenic fungal species in both human and animal health.

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Fusaria are the most economically significant fungi, as they are very prevalent in North American crops and can produce a wide variety of mycotoxins, the most important of which are deoxynivalenol (DON, vomitoxin), fumonisins, zearalenone, T-2 toxin and fusaric acid (FA).

The early 2015 growing season was consistently warm and damp in southwestern Ontario – ideal conditions for fungal development. We saw this in the early development of northern leaf blight in our corn crops. This is a fungal species identifiable by the long narrow lesions that appear parallel on the leaves of the plant.

Moist conditions activate this fungus, causing spores to transfer to plant tissue; visual signs of attack can soon follow. It is important to note that northern leaf blight itself does not produce mycotoxins.

Once infected, plants have a reduced immunity, and this gateway fungus can open the door to other potentially harmful mycotoxin-producing fungi. Infectious fungal spores easily move through air, water or direct contact.

This is why we saw increased levels of infections in years when climates are ideal for fungal growth: in the 2014 fall harvest and the spring wheat harvest in 2015.

We could also see the results in the reduced silage yields seen by some producers in the fall of 2015 where fungal growth conditions were ideal, as these fungi attack both the structural integrity of the plant and the grain itself.

To reduce the risk of fungal infection of your silage and grain crops, it is important to implement proper crop management techniques such as crop rotation, adequate tillage and considering planting resistant hybrid crops. Your local agronomist and seed representatives will offer solutions to mitigate the risks and have solutions to how to best combat fungal concerns in your field.

Warning signs for the presence of mycotoxins or fungi within the silage bunk are:

  • Hot pockets of silage in the bunker – The silage will be warm to the touch and indicate that aerobic fermentation is occurring and feed is being broken down.

  • Discolouration in the feed – These types of feeds should be avoided if possible and not fed to livestock as they present larger risks of containing mycotoxins.

  • Animals “off” when entering into a new section of bunk or silo – Could be seen as a sudden drop in milk, feed intake or reduced reproduction.

Prevention

The best way to prevent the harmful effect of mycotoxins is by minimizing the potential for fungi to produce these compounds pre-harvest. This can be done by harvesting the grain at maturity with minimal moisture and subsequently storing the grain under dry, cool conditions.

Chemical treatments such as ammonium isobutyrate or propionic acid can be applied to the harvested grain to minimize mycotoxin production in storage by eliminating the causal fungi. Such treatments kill the fungi that produce the mycotoxins and destroy the mycotoxins already present in the grain.

Minimize risk

Your feed adviser is willing and able to take samples of feeds on-farm to test for the presence of mycotoxins. With those results, they can work with you to put together an action plan to help reduce the effects of mycotoxins within your herd.

Mycotoxin binders come in a variety of forms and ideally adsorb mycotoxins in the lumen of the digestive tract to prevent intestinal absorption and transfer to target tissues within the animal. This offers a strong prevention if producers find themselves challenged with high levels of mycotoxins within their grains or forages on-farm.

It can be difficult to find mycotoxins within a bunker because it is a little bit like searching for a needle in a haystack. If there are production or reproduction issues on-farm, and the struggle continues to find an answer, using a mycotoxin binder is a good insurance policy.

Choosing one that covers a large number of mycotoxins will also help because, typically, there is never just one mycotoxin invading your feedstuffs; it is a cocktail.

Mycotoxins are a challenge dairy producers will continually face. Working with your local agronomist, seed provider and allowing for proper crop rotation and adequate tillage can help to limit fungal formation within crops. Proper storage and ensiling techniques help to limit the risk mycotoxins represent within your herd.

Additionally, a close working relationship with your feed adviser can help determine what issues you are being faced with through grain and forage testing, and additionally can help to develop solutions to offer safe, well-balanced feed to your dairy cows despite the challenges of mycotoxins.  PD

Maureen Bowman holds a master’s degree in animal science from University of Guelph and is a New-Life Mills dairy specialist working in southern Ontario. She can be reached by email.

PHOTO: Consistently warm and damp weather is an ideal condition for fungal development. Photo provided by New-Life Mills.

Maureen Bowman