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Maart 2016
FOCUS
Animal health
Special
Mycotoxins:
A menace to animal health
M
ycotoxins are small molecules produced as second-
ary metabolites by certain fungi. Currently up to 300
mycotoxins are known, but we will discuss those that
have been proven to be carcinogenic or toxigenic.
Three mycotoxins of economic importance includes aflatoxins,
fumonisins and zearalenone. These mycotoxins account for great
annual financial losses due to human and animal health and con-
demned or downgraded agricultural products.
Acute or chronic mycotoxicosis (disease caused by mycotoxins) can
result from exposure to feed or bedding contaminated with myco-
toxins (cereal, hay, straw, pastures, or any other fodder). Chronic
and acute effects of mycotoxins on animals (especially monogas-
trics) will depend on species and susceptibility of an animal within
a species.
The mycotoxin involved, amount and duration of the exposure, age,
health, and sex of the exposed animal and dietary status will also
play a role in chronic and acute effects.
Ruminants are generally more resistant to the adverse effects of
mycotoxins because microbiota in the rumen is capable of degrad-
ing mycotoxins. Sporadic outbreaks of mycotoxicosis in pets have
also been reported. In 2012, contaminated dog food resulted in the
death of 220 dogs in Gauteng, due to aflatoxicosis.
The cause of mycotoxicosis may not be immediately identified and
they are not transmissible from one animal to another. Treatment
with antibiotics will have little effect on the course of the disease.
Outbreaks are often seasonal, because particular climatic sequences
may favour fungal growth and mycotoxin production.
When inspecting the cause, a specific feed may be identified. Even
though fungi are present in feed, it is not an indication of the pres-
ence of mycotoxins. Although some fungi have the ability to produce
mycotoxins, they do not always produce mycotoxins.
It is therefore important to quantify these mycotoxins in feeds us-
ing various methods ranging from quick screening tests to more ad-
vanced methods used in laboratories.
Aflatoxins
The term mycotoxin was coined in 1962 when more than 100 000
turkey poults died in London, England. Turkey X disease was traced
to the consumption of
Aspergillus
spp. (
Photo 1
) contaminated
peanut meal.
The major aflatoxins are B
1
, B
2
, G
1
, and G
2
of which Aflatoxin B
1
is the
most potent natural carcinogen known. Aflatoxin M
1
and M
2
can be
produced in milk and dairy products. Aflatoxin contamination has
been linked to increased mortality in farm animals and thus signifi-
cantly lowers the value of grains as an animal feed and export com-
modity.
Aflatoxin is linked to toxicity and carcinogenicity in animals and is
termed aflatoxicosis. Chronic aflatoxicosis can result in cancer and
immune suppression and acute aflatoxicosis can result in death. The
liver is the primary target organ, with liver damage occurring when
poultry, fish, rodents and nonhuman primates are fed Aflatoxin B
1
.
Fumonisins
The fungi
Fusarium verticillioides
(
Photo 2
) and
F. proliferatum
have
the ability to produce Fumonisin B
1
, B
2
and B
3
of which Fumonisin B
1
is the most toxic. Fumonisin B
1
can promote liver tumours in rats
(
Photo 3
), pulmonary oedema in pigs and create lesions and holes
in the brains (leukoencephalomalacia) of equids (
Photo 4
). Affected
equids will start to stagger (
Photo 5
) and eventually collapse.
Zearalenone
Zearalenone is mainly produced by
F. graminearum
(
Photo 6
) as well
as other
Fusarium
spp. in maize, wheat, barley, oats and sorghum
substrates.
It exhibits oestrogen-like activity in certain farm animals such as cat-
tle, sheep and pigs. At low doses it increases the size of mammary
glands and reproductive organs. At higher doses zearalenone inter-
feres with conception, ovulation, implantation, foetal development
and the viability of newborn animals.
Good agricultural practices as weapon
against mycotoxins
Early/timeous harvesting reduces fungal infection of crops in the
field. It has been reported that early harvesting and threshing of
peanuts can lower aflatoxin levels and increase gross returns com-
pared to delayed harvesting.
Drying of agricultural products to low moisture levels is critical to
create less favourable conditions for fungal growth and subsequent
mycotoxin synthesis. Insects can distribute fungal spores from con-
taminated to uncontaminated products and therefore lower mois-
ture levels is also crucial to manage insects and fungal distribution.
During storage, transportation and marketing, maintenance of low
moisture levels should be maintained. Sorting of visually damaged
grains and separation from the bulk can remove a portion of my-
cotoxins. The removal and destruction of debris from previous har-
vests can minimise infection and infestation of produce in the field.
Chemical control could be applied during the production process to
minimise fungal infection due to insect infestations.
BELINDA JANSE VAN RENSBURG,
ARC-Grain Crops Institute, Potchefstroom