Fusarium Head Blight has become the most important cereal disease in Manitoba.
FHB was first reported in Manitoba in 1923. It then either disappeared or existed
at negligible levels until 1984 when the first outbreak hit Manitoba. The Canadian
Grain Commission began their annual surveying for the disease in 1985. At that
time, FHB was limited to the Red River Valley. Since the major outbreak in 1993,
FHB has spread north and west out of the Red River Valley , following the black
soil zone, into Saskatchewan and Alberta. Manitoba remains the hardest hit with
40% of wheat samples and 12% of barley samples infected with FHB in 1999. Sampling
in Saskatchewan and Alberta in 1999 showed infection in 2.6% and 0.5% of wheat
samples, respectively.



The high incidence of FHB has significance for livestock producers as FHB kernels
often contain a mycotoxin called deoxynivalenol (DON), also known as vomitoxin.
DON is a very mild mycotoxin. When present at high enough levels in the diet (>2ppm),
DON causes a reduced feed intake in swine. DON is of limited concern to cattle
producers because it is metabolized extensively in the rumen. Since the 1993 outbreak,
there has been considerable research into the effects of DON on beef, sheep and
dairy production.



Various research trials at the University of Minnesota and North Dakota State
University have shown that growing cattle and sheep can be fed 12-18 ppm DON in
the total diet dry matter with no effect on feed intake, average daily gain or
feed efficiency. Rations with 10-12 ppm DON during mid and late gestation have
been shown to have no effect on reproduction in cattle or sheep.



Dairy cows also appear to tolerate relatively high levels of DON in their diets.
In an Agriculture Canada trial, heifers were fed rations containing 6.4 ppm DON
for 10 weeks during mid lactation with no effect on production. Research at the
University of Manitoba showed that heavily contaminated barley (with 24 ppm DON),
could be fed to provide up to 8.4 ppm DON in total ration dry matter. This had
no effect on dry matter intake, milk yield or milk components of cows producing
over 33 kg milk/day.



DON belongs to a family of mycotoxins called tricothecenes. Tricothecenes are
protein inhibitors and it has been speculated that animals fed high levels of
tricothecenes may have a weakened immune system. However, DON is a very mild toxin
compared to other tricothecenes. It is also extensively metabolized, poorly absorbed
and rapidly cleared from tissues and fluids in ruminants. There is no evidence
to support depressed immune function, even in pigs, which are much more sensitive
to DON.



For many years, DON was believed to be a marker for other toxins i.e. the presence
of DON would indicate the presence of other toxins that were more difficult and
costly to analyze. A recent report from North Dakota State University called this
belief into question. The toxicology lab summarized the results of 8,000 feed
samples that were each tested for 17 mycotoxins between 1990 and 1999. Thirty
nine percent of samples contained DON but only 8% of samples contained other mycotoxins.
Based on this information, DON does not appear to be a significant marker for
other mycotoxins.



DON is rapidly excreted and does not accumulate in milk or animal tissues. Residues,
in animal products destined for human consumption, are not a concern when feeding
grain with DON.



When feeding any moldy feedstuff, producers need to take into account the other
quality issues associated with moldy feed(eg. palatability, energy loss).