They are also a potential food safety risk, says Smith, of Ontario Agricultural College at the University of Guelph. New Zealand dairy is becoming more exposed to them because of drought and the move towards more supplementary feed.
Smith was in Auckland recently, as a consultant to Alltech which held a one-day conference on mycotoxins.
Negative effects of mycotoxins on dairy cows include behaviour changes, reduced dry matter intake, loss of appetite and loss of muscle coordination, he says. Ingestion of contaminated feed produces an almost sedative like affect. The animals are lethargic and want to lie down, not forage around.
A second group of symptoms includes various lesions in the digestive tract of the cow. These can lead to haemorrhaging or bleeding. Conditions such as haemorrhagic bowel syndrome, for instance, are made more severe. There can be an increased frequency of ulcers, blood in faeces and damage to the villi of the intestine which inhibits nutrient uptake.
A third group of symptoms relates to feed-borne mycotoxins’ suppression of the immune system. “This means the dairy cows can experience lingering disease problems; we can see animals that do not respond to medications. We can also see failure of vaccination programmes.
“The overall effect is a deterioration of health status in the herd. We can see increased mortalities, and the challenge is the symptoms we see in the mortalities are not what we would call mycotoxin lesions – they arise from the organisms which took advantage of the compromised immunity. So it’s difficult for veterinarians to conclude that this was mycotoxin-induced.”
A fourth group of symptoms involving contaminated feed is impaired reproduction, he says. “We see decreased fertility and increased frequency of abortions. This is because a few of these mycotoxin compounds are estrogenic so they affect hormonal balance in the dairy cow.”
Smith says the other aspect of the mycotoxin challenge in the dairy cow is food safety issue. The residues in fluid milk known as aflatoxins are carcinogenic – one of the most carcinogenic compounds we know of.
The form of aflatoxin in feedstuffs is somewhat different from the form in milk, which is called alflatoxin M1 – M for milk. “This is less carcinogenic than the compound in feedstuffs but it can present a hazard especially for infant formulas.
“This is a human food safety issue – the levels threatening to humans are not levels that would affect the performance or health of cows. Dairy cows can tolerate much higher levels than those in condemned milk.
“It’s a food safety issue for export markets and preserving the image of New Zealand dairy products; they have to make certain the aflatoxin levels are not exceeded.”
One concept addressed in the mycotoxin conference was some new technologies developed for measuring mycotoxin levels in dairy feedstuffs.
One technology has been pioneered by the Alltech research group at its headquarters in Lexington, Kentucky. This is a technology known as LC/MS/MS and it allows multiple compound analysis. Alltech scientists have developed technology to allow simultaneous detection of 37 different compounds.
Testing of feedstuffs fed to dairy cows – including a mixture of New Zealand produced feedstuffs and some imported – showed they all contained more than one toxin and typically the average was 6.3 different mycotoxins. 22% tested positive for aflatoxin.
“It doesn’t mean they were in exceptionally high levels but it does mean that aflatoxin is present in feedstuffs being fed in New Zealand. Under certain circumstances this could result in condemnation of milk for human consumption.”
Milk is constantly being tested for the aflatoxin M1, given its danger to human health. But testing at feed level will be a further backstop against it getting into the milk.
“But testing at feed level will also minimise the exposure of the cows to contaminated feed,” says Smith. “This not only means the milk will be more wholesome but these compounds suppress immunity and increase disease susceptibility in animals.”
The LC/MS/MS test is only available in sophisticated laboratories and is only economical for large companies to carry out. But an option for smaller operators such as feed mills or farmers is the Elisa test which tests for individual mycotoxins and costs about $15, says Smith.
