active components such as sucrose and
oligosaccharides. Inactivation is critically
dependent upon alcohol concentrations
and temperature. Maximum efficiency is
achieved with proportions of 0.65–0.70
ethanol at 78°C. Ethanol extraction of soy-
bean removes antigenicity and prevents gut
inflammatory reactions in the calf, but
other procedures, such as alkali treatment,
are necessary for enhancing the nutritive
value of soybean protein for early weaning
of piglets. At least two soybean products
are now available for commercial use in
calf and piglet diets. The products are
guaranteed free of antigens, but the nature
of the processing techniques used remains
undisclosed.
In the case of CTs, limited evidence
suggests that dietary supplements such as
polyethylene glycol 4000 (PEG-4000) or
urea may be effective for ruminants fed on
high-tannin browse legumes. CTs bind to
PEG-4000 in preference to protein. Dietary
protein thus becomes available for digestion
and, in addition, activities of endogenous
proteins and enzymes remain unaffected
(Kumar and D’Mello, 1995). However,
indiscriminate use of PEG-4000 may well
compromise the bloat-retarding properties
of CTs. An alternative approach based on
urea supplementation has been found to be
useful in farm conditions. Urea not only
provides additional nitrogen, but it may
also inactivate CTs.
Considerable amelioration, or even
avoidance, of adverse effects in ruminants
may be achieved by employing suitable
grazing strategies. Current recommenda-
tions for the prevention of SMCO toxicity
in sheep involve some control of Brassica
intake, particularly in late winter when
SMCO concentrations in the forage are
maximal. In addition, further control of
SMCO intake may be accomplished by
feeding Brassica forage grown on low-
sulphur soils which reduces SMCO levels
in the crop. Mimosine toxicity in
Leucaena-fed sheep may be averted by
gradually increasing dietary concentrations
of the legume over a 3-week period.
Management strategies are also
advocated for reducing the adverse effects
of endophyte-infected grasses, since the
introduction of endophyte-free cultivars is
accompanied by agronomic disadvantages.
Thus, managing grazing to maintain the
grass in a vegetative state reduces toxicity
by preventing consumption of seedheads
which contain higher levels of the
endophyte mycotoxins. Rotational grazing
involving pastures free of endophyte-
infected grasses, particularly in hot weather
to offset heat stress, has been advanced as
an additional measure.
With other mycotoxins, preventive
rather than curative or management
measures are necessary to ensure that
performance and animal product safety are
not compromised. When fungicides are
used effectively to control fungal diseases
of crop plants, then the risk of mycotoxin
contamination of primary feeds may be
minimized. However, in the case of certain
Fusarium diseases of cereals, it is generally
accepted that fungicide control is only
partially effective and the potential exists
for mycotoxin contamination of grain. One
possible strategy, with environmental
dividends, centres on plant selection and
breeding. Experimental studies show that,
for example, breeding maize plants that are
resistant to colonization and ear rot caused
by A. flavus generally results in lower
contamination of grain with AFB 1.
Similarly, exploitation of genetic resistance
to Fusarium head blight in wheat can be
used successfully to reduce DON levels in
the grain. A similar approach is being
advocated in the control of lupinosis, with
the development of Phomopsis-resistant
cultivars of lupin. It is salutary to note that
plant selection and breeding have already
proved to be commercially successful in
reducing glucosinolate levels in rapeseed.
When mycotoxin contamination of
primary feed ingredients has occurred, a
number of damage-limitation and remedial
options are available. Thus, removal of
heavily contaminated outer layers of cereal
kernels has been attempted in order to
reduce DON. Dilution with feeds free of
contamination may also be advocated
within specified regulatory guidelines. In
the case of aflatoxin-contaminated oilseedsAnti-nutritional Factors and Mycotoxins 399