of Mycotoxins In Pigs
Mycotoxins are secondary metabolites
produced by moulds (microscopic fungi) growing in feedstuffs. Moulds
such as Fusarium spp. can grow on grain and produce mycotoxins before
harvest. Other moulds infect grain before harvest but produce most
mycotoxins during storage. The moulds that produce mycotoxins are
not always visible, but feed stuffs that become visibly mouldy during
storage are very likely to reduce productivity.
There are several key questions that should be considered when faced
with options on either the purchase of fungus-infected (often weather-damaged)
grain or the use of feed that has become mouldy in storage. Some
- whether fungal toxins (mycotoxins) are present in concentrations
sufficient to affect pig health and performance;
- whether the palatability and nutrient content has been altered
for better or worse, and the most important question of all;
- whether the lower price of the grain or other feed component,
compensates for these effects and the risks involved.
Many moulds cause only a slightly reduced growth
rate or poor feed conversion, but some mycotoxins with more drastic
effects are aflatoxins, ochratoxins, zearalenone, trichothecenes
(deoxynivalenol, nivalenol), fumonisins . These mycotoxins do occur
in particular regions and in particular situations, so that prior
knowledge of these circumstances will greatly reduce the risk of
The fungi that produce aflatoxins (Aspergillus flavus and A parasiticus)
most commonly grow during storage of summer crops (Corn, Soya and
sorghum) but wheat and barley can also be affected.
Typically, aflatoxin occurs on farms that mix their feeds from home-grown
grain. Failure to dry grain, or moisture condensation and accumulation
favour the growth of moulds, which is accompanied by heating - these
moulds grow best at 30-40 degrees. Aflatoxins can be produced within
2-6 weeks and signs of mycotoxicosis of pigs may be noticed within
a week of it being introduced to the diet.
The clinical signs of aflatoxin poisoning are not characteristic.
Pigs go off their feed and some may die, some are anaemic (pale)
and jaundiced (yellowish in colour). Characteristic damage is caused
to the liver, that can be detected when it is examined post mortem,
and a diagnosis of aflatoxiicosis is confirmed when the feed and
tissues from dead animals are analysed at a laboratory.
There is no specific treatment for affected pigs. Replace or dilute
the mouldy feed with clean feed containing adequate protein, as
the effects of aflatoxin poisoning are made worse by low dietary
protein. Pigs may take several weeks to recover and never reach
their normal growth potential.
Overall, the main risks are grain that has been stored moist and
heated in the silo. Although less frequent, mouldy corn, barley
and wheat can on occasion contain enough aflatoxins to seriously
Ochratoxin A is produced by a number of Aspergillus and Penicilllum
fungi. Ochratoxin A may occur in combination with citrinin, and
both of these mycotoxins cause kidney damage. Depressed appetite
and reduced growth rate may result. Ochratoxin A is a common contaminant
of barley grown in cool to wet conditions in northern Europe and
Canada. . However, ochratoxicosis of pigs is not common in Latin
Zearalenone is the most detrimental mycotoxin in Pigs with some
properties of the female sex hormone oestrogen. Several Fusarium
moulds produce it in grains, particularly corn, grown in cool, wetter
regions. The fungus actually grows on the grain before harvest when
rainfall is high and insect damage prevalent, but damp, cool storage
after harvest increases the hazard. When fed to female grower pigs,
zearalenone causes swelling and reddening of the vulva similar to
that seen at natural heat. This can progress to straining and prolapse
of the rectum and vagina. Zearalenone also causes slight development
of the teats of gilts and occasionally swelling of the prepuce of
boars. A dark purple discolouration of maize or pink tips on bleached
wheat may be an indication of infection with zearalenone-producing
mould, but it can also be present in weather-damaged sorghum. Diagnosis
is confirmed by analysis of the feed. Zearalenone toxicosis is increasing
in North and South America.
This group of mycotoxins includes deoxynivalenol, which is occasionally
detected in Corn, Wheat . If the pigs are hungry when the feed is
first offered, they may eat and then vomit, which is why deoxynivalenol
is also called vomitoxin. . A purple-red mould (Fusarium graminearum)
infecting wheat, corn and Soybeans before harvest produces these
mycotoxins, often in conjunction with zearalenone. There are a few
other trichothecenes, including T2-toxin, HT-2,which could potentially
Fumonisins are common in maize infected with Fusarium moniliforme
in most temperate regions of the world.. Fumonisins can be produced
before harvest. They have been associated with pulmonary oedema
(fluid in the lungs) of pigs in the USA.
Effects of moulds on palatability and nutrients
The only mycotoxins that have so far been shown to affect pigs are
aflatoxins, zearalenone, deoxynivalenol . As described above, these
occur in particular circumstances, and knowledge of those circumstances
will help to reduce risk of Mycotoxicosis.
Mould growth before harvest
In general, changes in palatability and nutrient content of grain
infected with mould before harvest (weather-damage) is slight, and
there may even be some improvement in nutritive value as a result
of starch hydrolysis similar to that seen in early germination.
Deteriorated grain will be lighter in weight, be discoloured and
darkened if mould invasion is extensive and the endosperm is likely
to have a chalky appearance due to the partial hydrolysis of the
nutrient stores. Gross energy on a weight basis may be unaffected,
but fiber and non-protein nitrogen may be increased. The minor nutritional
deficiencies of weather-damaged grains can generally be ignored
in dietary formulation, but if desired, increasing the digestible
energy with fat can easily compensate .
Mould growth in storage
Many moulds can grow in stored feed when hygiene is poor. Mould
spores are always present in feed and the main factor stopping mould
growth is lack of moisture. Condensation, leaks, rodent and insect
damage all lead to mould growth. When this has occurred, the main
affects are reduced palatability and worsening of feed conversion.
These effects should not be ignored, as the effects on profits can
be severe. Mould infection of grain decreases its feed value for
pigs through the removal of storage starch and the hydrolysis of
protein and losses in fat content also occur. Consequently, in material
with extensive mould invasion during storage, the relative amount
of fibre in the grain will increase in proportion to the decline
in starch, protein components and fats, leading to reductions in
digestible energy content. Vitamins and other essential nutrients
can also be affected. The result of these changes is poor conversion
of feed . Regular cleaning of silos and feed handling equipment,
and rapid feed turn over are very important to maintain feed quality.
Sometimes in times of high humidity, feed may become slightly mouldy
despite good hygiene and there is a need to use this material. Damaged
feed that has undergone fungal growth during storage may exhibit
'off' aromas and flavours and be unpalatable when first offered
to pigs. Usually, this poor palatability lasts only a few days before
pigs become accustomed to the taste and smell. If it persists longer
than this, it might indicate infectious disease or dietary imbalance,
although mycotoxins are a possibility.
The decision whether or not to feed weather-damaged grain or mouldy
feed is a matter of balancing the risk of reduced growth with lower
feed costs Avoid feeding any unpalatable feed to young pigs, as
reduced intakes when young will compromise later performance. .
Finishers are a better proposition for unpalatable feed as slightly
reduced intakes may be desirable to reduce fat deposition, and actually
improve feed conversion slightly. Should feed conversion be adversely
affected, as will happen if nutrients are unbalanced or if there
are toxins in the feed, profits will reduce substantially. Risks
can also be minimised by checking for zearealenone contaminated
feed for sows in the gestation/lactation phase where possible.
Ing: José E. Ferrer
AGRANCO CORP. (USA)