With aerobic work, there really isn't much lactic
acid production to speak of. Lactic acid is a byproduct of anaerobic
metabolism. Horses conditioned to do distance that have an abundance of
slow-twitch muscle fibers just don't get acidotic working at the speeds that our
horses work. So virtually all shifts in the endurance horse are
toward an alkalotic state. So in the healthy endurance horse,
the alkalotic shift isn't as severe as you may be thinking--it is simply
more alkalotic than normal, rather than having to "overcome" any
acidosis.
And yes, horses lose A LOT of chloride in
sweat--but how much of a deficit this causes is also relative to how much
of a forage fill they have in the hindgut, which serves as a reservoir for
electrolytes and fluids to some degree--an adaptation that humans don't
have. (Nor do humans have the VFA production in a hindgut for energy, the
way horses do--horses really are the consumate endurance animals!) But
loss of chloride and other e-lytes is of course why electrolyte supplementation
is such a hot topic for our horses as well.
As to references for reading--I don't know of any
specific texts on the subject, but perhaps Susan G can weigh in here with some
good papers to which to refer you. She's much better at scrounging through
the literature than I am, and much of the stuff I've got in my files is older
work.
Sorry Heidi, my question (previous
reply) wasn't quite thought out enough. Did you mean that a horse
looses sufficient chloride in sweat to override lactic acid
production from muscle exertion & hypovolemia? WOW
> It amazes me that even
among some experienced riders there isn't a clear understanding that
metabolic acidosis and electrolyte imbalance can lead to sudden cardiac
death and that it takes more than IV fluids to get passed that
possibility.
Endurance horses are alkalotic, rather than
acidotic. Metabolic alkalosis is particularly an issue, given the
losses of chlorides, but respiratory alkalosis can be an issue in some as
well. But even so, you are right that simply putting the horses on IV
fluids often isn't the whole story.
