How to deal with mycotoxins and the heat

How to deal with mycotoxins and the heat

22 October 2018

The hot and humid days of summer go hand-in-hand with mycotoxins and the animal health issues they can cause. SealesWinslow’s Science Extension Officer, Natalie Hughes, outlines some practical and proven strategies for dealing with this seasonal challenge.

When the temperatures rise, mycotoxins can cause a drop in dairy cow feed intake and performance, rough coats, lethargy and behavioural changes.

Mycotoxins – groups of toxic fungi and their spores – are troublesome summer visitors that can grow on practically any feed source, including pasture treated with endophyte. It can present as mould (typically invisible to the human eye) and thrives when conditions are warm and humid. Various types of mycotoxins are found in the base of ryegrass or on supplementary feed such as silage, baleage and grains. Depending on the type of toxin and the level of intake by the animal, it may cause chronic or acute effects such as feed refusal and a drop in production or liveweight gain.

Mycotoxin levels are notoriously difficult to assess via testing. In silage stacks, for instance, they tend to concentrate around air pockets so require a careful selection of sample testing sites. Any visible signs of mould on feed demands extreme caution. and should never be given to lactating or dry pregnant cows due to the reduced milk production and risk of abortion.

The solution is dilution

When you’re faced with high levels of mycotoxins in your pasture or feed "the solution is dilution!"

"Fundamentally, the overarching strategy is to mitigate the exposure by providing alternative feed sources," Natalie explains. "If the primary feed source is compromised, provide a high-quality supplement to effectively dilute the mycotoxin component of the diet."

While the rumen of a cow can naturally deal with small quantities of some toxins, the situation quickly becomes problematic when high humidity promotes the growth of spores. Given that pasture is typically a large proportion of the diet, this represents an increased risk. So it pays to take extra care after a drought when there’s a sudden rise in humidity.

Natalie recommends some general precautions such as maintaining clean silage faces and taking preferential care of young stock due to their lower tolerance levels. In terms of pasture management, it’s helpful to avoid hard grazing (because the fungus resides at the base of the plant) and promote the growth of clover because it’s endophyte-free and therefore doesn’t host mycotoxins. Similarly, newer pastures containing no endophyte or one of the novel endophytes that carry a much lower risk are best. If mycotoxin levels become too high, the addition of mycotoxin binders is another way to reduce the impact.

Added heat stress

Unfortunately, the ideal growing conditions for mycotoxins coincides with naturally high temperatures outside the optimal conditions for cows. "The thermal neutral zone for cows is between 5 and 20 degrees," says Natalie. "Outside of this zone, animals become selective eaters to reduce the heat generated in the rumen. This dual challenge results in reduced dry matter intake, a reduced milk production and an increased risk of acidosis."

One of the best ways of addressing these factors is to supplement with high-quality pellets. SealesWinslow has a range of formulations that can be tailored to include minerals to support the immune system and additives to optimise the all-important rumen health. Equally important is the inclusion of ‘binders’ - additives that bind and/or detoxify the harmful mycotoxins and prevent absorption by the animal.

While it’s impossible to remove all mycotoxins from pasture or feed, these suggestions will go a long way to keep your animals healthy and maintain good production levels.

For more information, head to your local Farm Source store. or visit

Article supplied by SealesWinslow