The frequency of mycotoxin contamination of feeds appears to be increasing, according to a specialist in the field.
Mycotoxins are toxic metabolites produced by molds.
Scientists’ understanding of the economic significance of feed-borne mycotoxins has often paralleled advances in the tests used to measure their levels in feeds, according to Professor Trevor Smith, of the University of Guelph in Ontario, Canada.
Smith, writing in the latest issue of Equine Disease Quarterly, said aflatoxin was a mycotoxin produced mainly by the molds Aspergillus flavus and Aspergillus parasiticus, which are generally considered to be tropical or semi-tropical fungi thriving under conditions of high temperature and humidity.
Four chemical forms of aflatoxin can be measured simultaneously by many commercial laboratories.
“Horses, like many other species, are very sensitive to feed-borne aflatoxins,” he said. Aflatoxins mainly target the liver, causing necrosis and potentially cancer.
However, more common on a global basis are several hundred identified Fusarium mycotoxins.
The study of Fusarium mycotoxicoses was considerably more complex than the study of aflatoxicosis, he said.
Fusarium fungi thrive in soils from areas with temperate climates including North America, much of Europe and Asia and South America.
The most common Fusarium mycotoxins include DON (also known by the chemical name deoxynivalenol or the common name vomitoxin), zearalenone, fumonisin, and fusaric acid.
The feeding of blends of grains naturally contaminated with Fusarium mycotoxins, largely DON, has been reported to cause reduced concentrate consumption by sedentary mares with some evidence of liver damage also detected.
However, imposition of an exercise regime resulted in increased concentrate consumption but weight loss was then also noted.
Horses are particularly sensitive to feed-borne fumonisin, which can cause deaths due to equine leukoencephalomalacia. This brain disease is also more commonly known as “moldy corn poisoning”.
“The most significant current controversy regarding feed-borne mycotoxins is the concept of conjugated or ‘masked’ mycotoxins,” Smith said.
“These are mycotoxins that are produced by molds on feedstuffs preharvest and then chemically modified by the plants invaded by the molds.
“These modified mycotoxins are thought to be toxic, but non-detectable by analytical techniques currently used by most commercial laboratories.”
Scientists were actively studying these compounds in order to understand their importance, he said.
“It appears that the frequency of mycotoxin contamination of feedstuffs is increasing.
“This may be due, in part, to unfavorable growing conditions caused by extreme weather,” he said, noting that 2012 was a year of significant drought in the corn-growing regions of North America.
“The levels of fumonisin contamination were unusually high and fumonisin was detected in significant quantities in corn grown in regions where fumonisin contamination has been rare in the past.”
Improved analytical techniques for mycotoxin detection were needed to minimize exposure of horses to contaminated feeds and forages in the future, Smith said.
Equine Disease Quarterly is funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents.