THE frequency of mycotoxin issues in stock feed has increased substantially over the past decade, according to a specialist who recently visited Australia.
Mycotoxins - toxic metabolites produced by moulds - have been a common issue in the feed industry for many years, Trevor Smith from the Department of Animal and Poultry Science at the University of Guelph in Ontario, Canada, said.
"We began research at Guelph in 1977, and at that time it was common for us to have mycotoxin issues in the animal industries maybe every third year or so," Professor Smith said.
"But over the last decade or so, the frequency of mycotoxin challenges is increasing quite substantially."
Global climate change and extreme weather conditions around the world were key factors in this aspect.
"Certainly excess moisture in the growing season and at harvest is a key factor in promoting mould growth and toxin production," Prof Smith said.
"Drought also does this - the fungus responds to any type of environmental stress by producing more toxin.
"The mixture of toxins may vary but the net effect is at either extreme of weather, there are way more toxin challenges."
Also making the toxin problem bigger is the fact that livestock diets contain many different ingredients which could have very different geographical origins.
"This means that when we look at any livestock feed we will see multiple co-contaminants - not one or two, but maybe 10 or 20."
While many of these co-contaminants might be low in concentrations, there were two damaging effects which could occur, Prof Smith said.
One was additive, meaning that a number of toxins - even at low levels - added together may have a significant effect on animal health.
Second was the possibility of so-called toxicological synergy, where the presence of one toxin increased the toxicity of another.
"And so with the complex nature of the diets, we have more extreme responses in animals than we would expect based on individual toxins," Prof Smith said.
Due to their rumen microorganisms, ruminants had greater natural defences when it came to mycotoxins.
In particular, protozoa enzymes could partially inactivate the toxins.
"But the challenge with ruminants is that the diet is more complex than for monogastrics; the big component to that is silages," he said.
"We can group the toxins into two groups: field toxins, which become established in the field because the mould is growing in the soil and the plants become contaminated pre-harvest.
"Then we have so-called storage mycotoxins, and these are due to the growth of fungi on plant material post-harvest - such as silages.
"So we have a very complex mixture presented to the rumen."
Of the two groups, Prof Smith said understanding of field toxins was better with respect to the effects on animals.
"We have quite a bit of data in monogastrics as well as ruminants for the various field toxins.
"The most significant would be produced by fusarium moulds; fusarium fungi grow in the soil in more temperate climates - that certainly would include a lot of the soils in Australia, so fusarium mycotoxins will be quantitatively most significant.
"But the toxins found in silages are generally more of the aspergillus and penicillum varieties."
* Full report in Stock Journal, November 13, 2014 issue.