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Common Misconceptions
Many people tend to believe that, because of the
size and physical abilities of horses, they are tough, hardy and
invincible. This isn't the case, at least as far as plant toxins
go. They are no more immune to toxins than a dog, cat, or even a
human. Due to sheer weight and size, equines may be able to
ingest more of a toxic material before becoming ill, but not more
per pound of body weight than other animals, at least not for the vast
majority of poisons.
There is a common belief that if cattle can graze an area
without ill effects, then horses can too. This is true, up to a point. However,
horses may select for (choose) different forages than other livestock, which can result
in a diet with a significantly different composition from those of cattle,
goats, or sheep, which in turn may result in problems for the horse. It may not
be the best thing for your horse, nutritionally speaking, to graze along with
cattle without being monitored periodically.
"My horse has
been eating that for years, and there's nothing wrong with him!"
Maybe, maybe not. Some toxins don't have immediate effects or symptoms, but
years of ingestion could cause a buildup that eventually is toxic. In
addition, toxins that work on the liver may present no symptoms until the liver
is damaged beyond repair, at which time symptoms will appear.
"One
horse requires one acre of pasture." In some cases, true. However,
that old rule of thumb doesn't apply to all horses in all pastures in all areas.
Forage type, quality, density, and growth all vary, within areas and from year to year.
The same grass that was prevalent last year in your pasture may not be dominant
this year, due to temperature differences, last year's grazing, or precipitation amounts. There are
areas of the West that require a dozen acres to sustain one horse, and there are
also areas in which half of an acre would be sufficient. Horse condition and
pasture condition are the clues to whether or not your pasture supports your
animals.
"Horses can't graze tall fescue: it's
toxic." Some plants have little toxic effect on most horses, but can
cause problems in pregnancy or deformed foals if ingested by broodmares. Most of
these are tolerated well by the majority of horses, and can safely be used in
most pastures. "The rest of my horses are fine, so ol' Molly
can't be sick from plant poisons." Not all horses react to all toxins
uniformly. In other words: age, condition, and prior or underlying health
problems all have an effect on the animal's metabolization of toxins. 'Ol
Molly's system may just be aged and depleted enough that it can't handle the
same toxins the other horses are ingesting without ill effects.
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