destined for animal feed, however, specific
detoxification procedures are commercially
available in a number of countries.
Ammoniation of contaminated oilseed
meals appears to be the method of choice,
involving treatment with either ammonium
hydroxide or gaseous ammonia at high
temperatures and pressure, as in commer-
cial feed mills, or at ambient temperature
and low pressure for small-scale opera-
tions. If the ammoniation reactions are
allowed to proceed to completion, the
detoxification process is irreversible and
aflatoxin contamination is virtually
eliminated. Providing that any residual
ammonia is dissipated, diets containing de-
contaminated meals are readily consumed
by farm animals without adverse effects.
Depending upon the efficacy of decon-
tamination, residues of AFM 1 in the milk
of dairy cows are substantially reduced or
eliminated altogether. The use of phyllo-
silicate clays (hydrated sodium calcium
aluminosilicate) to complex with aflatoxins
has also been attempted, resulting in
reduced gut uptake and deposition of the
mycotoxins in tissues and milk.
Future developments in preventive
and remedial measures are likely to emerge
from biotechnology. There is already
practical evidence of the effectiveness of
such strategies. Thus, Leucaena toxicity in
cattle, arising from the two DHP products
of mimosine metabolism, has been over-
come in Australia by inoculating animals
with bacteria capable of completely
degrading these metabolites to non-toxic
compounds (see D’Mello, 1992). Dosed
animals feeding on Leucaena show
markedly higher liveweight gains than
untreated controls on the same legume.
Excretion of DHP in urine of dosed steers
declines rapidly to zero, whereas untreated
steers on Leucaena continue to excrete
DHP. The dispersal of bacteria to untreated
animals occurs rapidly, and the isolation of
active DHP-degrading bacteria from faeces
of treated cattle indicates that inoculation
of just a few animals in a herd may be all
that is required to overcome Leucaena
toxicity. This type of bioremediation may
be applied to other ANFs and, indeed, to
mycotoxins. There is evidence of bacterial
degradation of tannins, DON and ZEN.Regulatory and Advisory Directives
The acute toxicity of certain secondary
compounds, and in particular the carcino-
genicity of mycotoxins, has led to the
establishment of regulatory and advisory
directives for primary feed ingredients and
complete rations. Table 18.7 is designed to
illustrate the type of directives in place in
the UK, the European Union (EU) and in
North America. Two plant secondary
compounds, gossypol and HCN, are subject
to statutory control. In addition, EU quality
criteria have been published for gluco-
sinolates in rapeseed. For CTs in lotus,
Barry et al. (1986) recommended appro-
priate concentrations in the forage dry
matter, to represent a balance between the
beneficial effects for protein protection in
the rumen and bloat suppression, and their
negative effects in depressing microbial
fermentation of structural carbohydrates.
Extensive regulations also exist for the
aflatoxins, but for OA and DON only
advisory directives have been proposed,
unsupported by legislative measures. Of
particular concern is the absence of
statutory regulations for the carcinogenic
fumonisins.Conclusions
Plants and fungi synthesize a wide range of
substances with anti-nutritional and toxic
effects in farm animals. Extensive rumen
and tissue metabolism may occur in farm
animals to initiate or enhance the potency
of some of these compounds. Plant com-
ponents with significant anti-nutritional
activity include lectins, proteinase
inhibitors, antigenic proteins, CTs, quino-
lizidine alkaloids, glucosinolates, non-
protein amino acids and phyto-oestrogens.
A number of these and other compounds
such as saponins, vasoactive lipids,
gossypol and HCN are associated with
toxic and anti-physiological effects. These400 J.P.F. D’Mello