Equine Factors in Plant Poisoning
There are physiological and behavioral factors which are very specific to
equines that may instigate, or even mitigate, toxic events.
The tolerance for toxins may vary between horses, depending upon factors
such as size or weight, age, nutritional condition, and pre-existing health
issues or disorders.
Poor physical condition is one element that can have a direct
effect on an animal’s response to toxins and recovery from poisoning. It is
perhaps the single attribute of a horse over which its owner has control, and
also the factor that is easiest to modify. An animal’s weight is significant
because it affects the amount of toxin the animal can ingest before it becomes a
critical amount, since lethal dose is related to percentage of body weight.
Improving an animal’s condition through diet and nutrition often leads
to more rapid detoxification, lessening of toxic effects, and damage from toxic
compounds.
Individual animals vary in their ability to handle inadequate or
excessive minerals and vitamins. However, it is accepted that either excessive
or deficient levels of these can impact livestock health and production, which
could subsequently affect susceptibility to toxic plants. Vitamins are often catalysts for metabolism, which means that
proper amounts are beneficial for the animal’s entire system.
Deficiencies may result in severe illness, while an excess may lead to
serious side effects. Selenium is one mineral that can have deleterious effects if
present in disproportionate amounts in equine diets; this will be covered later
in the section on toxins. Logic and
common sense dictate that any equine’s health and ability to cope with illness
depends on proper diet and nutrition.
Other factors that may affect a horse’s individual ability to
handle toxins are age and existing or prior health issues.
Age may be an issue with certain toxins. Ingestion of sensitive fern may be lethal if the animal is
quite old, while young animals are far more susceptible to the toxins in
locoweeds. Existing health issues
may make the horse more susceptible to toxins and may alter the course of
treatment. The owner and consulting
veterinarian must consider these on an individual basis.
The breed of horse has been named as a risk factor in some
studies for colic, which may mean that it also affects other gastric problems
including plant poisonings, though this has not yet been thoroughly
demonstrated.
The color of a horse has a recognized correlation to
susceptibility to some toxins. In
particular, toxin-induced photosensitization is far more likely in animals with
light-colored skin or skin patches.
The individual horse’s tolerance of or susceptibility to
poisons found in plants may be due in part to its grazing efficiency, which
varies between animals. This factor
includes the amount of unwanted plant matter ingested, and may possibly be used
to predict which horses are likely to be vulnerable to toxins.
There may exist
individual immunities within animals that are a result of long-term exposure to
certain poisonous plants. Horses raised on particular forage will continue to accept
that forage if it is offered. As a
group, equines are less immune and therefore more highly susceptible to some
toxins, including those found in tansy ragwort or stinking willie (Senecio
jacobaea), locoweeds, and the nightshade family (Solanum spp.).
Return to Problem Synopsis
|