Endurance.Net Ridecamp Archives

The instructor
> is supposedly an expert in the field of parasites, and yet when I asked
the
> direct question of long term damage, he said that other than colic that
can
> occur when a badly infested horse is first wormed, that there was no
> permanent damage to horses.
That's what we were taught in vet school as well (plus I checked again with
CSU's parasitologist as well), and there is research data to back it up.  By
far, most of the risk occurs actually during a current infestation, but the
damage does heal.  The parasite most likely to cause damage needing some
re-grouping on the part of the horse is Strongylus vulgaris, which migrates
through the blood vessels in the mesentery (which holds the small intestine
in place).  If enough worms clog up the blood vessels, parts of the
intestine are deprived of blood circulation and can cause colic to one
extent or another.  If the blockage is severe enough, the blood vessels
thrombose and are permanently blocked.  The good news is that horses are
very good at developing collateral circulation, that is, creating new
vessels to get around the roadblock (otherwise that portion of the gut would
die and cause massive peritonitis).  A very neat evolutionary trick.
Anyway, until those collateral vessels restore blood flow, the horse is at
risk for developing colic, but once everything is patent again, then there's
no long term effect to worry about.

Susan G



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