The Rural Voice, 1990-08, Page 16NEW & USED r
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12 THE RURAL VOICE
DIAGNOSTIC
TESTING LIVESTOCK FOR TOXINS
by Dr. G.K.A. Josephson — VETERINARY LABORATORY SERVICES
All of our drugs, pesticides, herb-
icides, parasiticides, and other sub-
stances that control, regulate, or de-
stroy organs, organisms, or undesir-
able cell populations can be classified
as poisons. When used as directed
against a specific pest, be it an insect
or plant, they are beneficial. How-
ever, when used in excess, when they
accumulate in the environment, or
when they enter or are consumed by
others than their targeted group, they
can cause serious problems.
A good example of the latter is
DDT, the first chlorinated hydro-
carbon insecticide to be used exten-
sively in agriculture. It tends to be
stored in body tissues, and accum-
ulates in higher concentrations as
you move up the food chain. Levels
in fish eating birds can become
excessive. This is also a good
example of a chronic toxicity, where
the harmful side effects may take
months or even years to develop.
In veterinary toxicology, numer-
ous factors influence the action of
poisonous substances. They include
(1) the dose, (2) the physical and
chemical nature of the poison, (3) the
source of the poison, (4) whether
exposure is single or repeated, (5) the
species of the animal, (6) the size,
age, and sex of the animal, (7) the
general state of health of the animal,
and (8) the route of absorption or
administration.
The usual route of exposure is
oral, with inhalation and absorption
through the skin only occasionally
seen. When poisons are taken orally,
much of the absorption takes place in
the intestine. Causing the animal to
vomit immediately after ingesting,
the product will therefore reduce
absorption. Similarly, diarrhea tends
to retard absorption of most products.
Cases of sickness or death result-
ing from products applied to the skin
are usually limited to overdosing with
insecticides used against internal or
external parasites.
The inhalation route is seen in
cases of carbon monoxide or carbon
dioxide exposure. Many herbicides
and insecticides can be absorbed
through the lungs, but these animals
must be housed in a confined area,
where air levels of the pesticide are
quite high.
With the exception of some caustic
compounds, most poisons are
absorbed and carried in the blood
stream to other parts of the body,
where they have their effect. Blood
can therefore be analyzed for the
presence of the toxic agent.
Toxic agents can be excreted
directly from the body, in the feces or
urine, but in most cases the animal
tries to change the chemical structure
of the product in an attempt to reduce
its toxic effect and to increase the rate
of excretion. This reaction, called
biotransformation, usually occurs in
the liver. Again, many factors affect
the animal's ability to detoxify a
particular agent. Newborn and very
old animals may lack specific
enzymes, and will be unable to
neutralize toxic products. Many
drugs are stored in body fat for
extremely long periods of time and
their detoxification is delayed.
OMAF's new Agriculture & Food
Laboratory Services Centre in Guelph,
on completion, will play an important
role in detecting low levels of toxic
agents (in parts per million and parts
per billion) in human food. This will
put even greater pressure on the pro-
ducer to ensure that his livestock are
not exposed unnecessarily to pest-
icides or other toxic agents, or if they
are exposed, to ensure that detectable
levels are not present in the meat.0