animal feed means that it is not always
possible to attribute adverse effects to a
particular compound. It will be clear from
the foregoing account that both lectins and
proteinase inhibitors are not only ubiquitous
but may also occur together in the seed of
the same leguminous plant. Studies with
the winged bean illustrate the circuitous
protocol employed in the identification of
the primary ANFs in leguminous seeds
(D’Mello, 1995). Thus, initial investigations
focused on the activity of the trypsin
inhibitors in the winged bean, but the
weight loss and high mortality of experi-
mental animals fed raw winged beans was
indicative of some other factor. Further
studies revealed the dominant role of
lectins in the aetiology of winged bean
toxicity. The soybean has long been recog-
nized for its content of proteinase
inhibitors, but recent studies indicate a
significant role for lectins and antigenic
globulins in the aetiology of post-weaning
hypersensitivity in calves and piglets. In
addition, the practical significance of the
phyto-oestrogens in soybean have yet to be
addressed with respect to farm animal
productivity.
Another issue requiring elucidation
centres on the protective role of CTs in the
microbial fermentation of protein in the
rumen. It is presumed that the CTs released
post-ruminally do not exert any deleterious
effects in the intestinal tract since pH
conditions do not allow further reactions
with dietary or endogenous proteins.
However, it has been observed that the CTs
of P. cineraria retain their capacity to
precipitate pepsin at pH 2.0 and, conse-
quently, an important digestive enzyme of
gastric secretion may be inhibited (see
Kumar and D’Mello, 1995). Furthermore,
Waghorn et al. (1994) maintain that the
benefits of protein protection may be offset,
in part, by a reduction in the fractional
absorption of essential as well as non-
essential amino acids from the small
intestine. A further question centres on the
dissociation of the protein–CT complex at
pH values below 4 and above 7. Since
these pH criteria also occur in non-
ruminants, the issue arises as to why such
a dissociation of the complex does not occur
in these animals or, if it does, why adverse
effects are observed in non-ruminants but
not in ruminants (D’Mello, 1992).
There is now unequivocal evidence of
co-contamination of animal feed with
mycotoxins of diverse origins. Thus, it is
conceivable that feeds based on groundnut
cake and maize consistently may be
contaminated with the aflatoxins and
fumonisins. The additive or synergistic
effects of these and other combinations
only recently have become the focus of
attention, providing improved understand-
ing of well-established cases of myco-
toxicoses. Thus, it is now recognized that
the ‘turkey X disease’ incident of 1960,
originally attributed to the aflatoxins, was
compounded by the co-occurrence of
cyclopiazonic acid, also produced by A.
flavus. Fusaric acid is a common
metabolite of several Fusarium species, co-
occurring with ZEN, DON and the
fumonisins. Although of minor intrinsic
toxicity at levels found in feeds, fusaric
acid can enhance the activity of other
Fusarium mycotoxins. Fusaric acid can
increase brain levels of serotonin in pigs,
and a potential synergistic interaction with
DON has been proposed in feed refusal and
emesis in these animals.Preventive and Remedial Measures
A selection of practical methods is
presented here to illustrate the diversity of
preventive and remedial measures avail-
able to the feed manufacturer and livestock
producer. With the thermolabile ANFs
such as lectins and proteinase inhibitors,
heat processing has long been the method
of choice for leguminous seeds containing
these substances. The efficacy of moist-
heating procedures as opposed to dry-
heating methods has been established.
Inactivation of soybean antigens, however,
requires more rigorous processing involv-
ing hot aqueous ethanol extraction. It is
suggested that detoxification is achieved by
altering the protein structure of the antigens
rather than by removal of osmotically398 J.P.F. D’Mello