Re: You can call me a pest now! :)

["Susan Evans Garlinghouse" <suendavid@worldnet.att.net>]

-----Original Message-----
From: Kristi Schaaf <iluvdez@yahoo.com>
To: Susan Evans Garlinghouse <suendavid@worldnet.att.net>
Date: Thursday, March 11, 1999 12:05 PM
Subject: You can call me a pest now! :)


>Susan -
>
>I don't want to take up too much more of your time after your
>wonderful response to my question, but here's another question for you
>to answer if you'd like....why does a seriously dehydrated horse not
>want to drink?

I should have mentioned in the original post that in triggering the thirst
response, an almost-the-same-thing-but-not-quite factor is plasma sodium
levels.  For example, let's say a horse is just standing around his stall,
losing the normal amount of fluids through respiration, urine, manure, etc,
but not alot of electrolytes because he's not sweating (actually, you do
lose electrolytes through manure and urine, etc, but not at the same rate as
you do through sweat).  While the horse is just standing there, and as the
water leaves the plasma, the blood becomes more "concentrated"---in other
words, saltier. Think of a glass of salty water left to evaporate for
while---the amount of water has reduced, but not the amount of salt, so the
remaining liquid is much saltier, right?   At a certain point, this
increased sodium concentration in the blood will also trigger the thirst
response, and the horse will go find his water trough.

Now let's take the horse who is dehydrated due to intense, prolonged
exercise, such as during a distance event.  The horse is losing alot of
fluid through sweat, but he's also losing electrolytes in the sweat.  Even
though the horse is increasingly dehydrated, the sodium response may not be
working well because the sodium concentration in the blood hasn't changed
enough to trigger the thirst response.  Think of that same glass of salty
water---but instead of letting the water evaporate, say you just pour out
half the fluid in the glass.  The total amount of fluid has changed, but the
saltiness of the fluid hasn't.  So even though the horse has lost alot of
fluid through sweating, his kidneys are looking at the sodium concentration
levels and saying nope, you're not thirsty.

You might think, ah hah, but if I force salt on him, then the plasma sodium
level will rise and he'll drink then, right?  But remember, if he's
dehydrated, the electrolytes won't be well absorbed, so that strategy
doesn't work all that well.  Or at least not without possibly having to move
some fluid from the plasma volume into the lumen of the gut---which may or
may not be a critical factor to the horse's well-being, depending on exactly
how dehydrated he is.  (That's why if my horse isn't drinking well yet, I
strongly prefer to slow down, possibly get some more hay into him, until the
system readjusts and tells him to drink already, or else try some other
tricks to encourage him to drink).

Eventually (hopefully not too long), the plasma volume will decrease enough
(usually around 10-12%) so that the kidneys notice the drop in blood
pressure/plasma volume and then will trigger the same cascade of hormones
that will trigger the thirst response.

.....oh, and one more question for you (Sorry!!), do you
>believe in pre-loading? I have used it and it worked (at the next ride
>on above horse; his metabolics were OUTSTANDING at the end - 180
>degree difference)...but maybe that's not the norm?

I don't believe in "pre-loading" exactly---the body doesn't store excess
electrolytes at all, it just pees it right back out.  Replacing a deficit is
fine.  Giving a small amount of electrolytes before the event is also fine,
so there'll be some 'lytes moving through the gut during exercise.  Whether
or not you give it later during the day depends on the particular
conditions, the horse, and how well he's drinking.  The big improvement you
saw in your horse (and congratulations, isn't that a charge to see that?)
may have been because he had a deficit before he started---some horses do
need more electrolytes on board than others.  You might play around with how
you're offering salt before the ride, some horses have preferences of one
type of salt over another.  If the horse has free access to good-quality hay
before the ride, then usually just plain old non-iodized, non-TM, loose salt
is all you need.  Also, if you're providing salt as a block, consider
providing it loose---some horse's tongues will get sore before they can lick
off all the salt they need and when stop, even though they are still
salt-deficient.

What I do believe in is making sure that salt is available free-choice at
all times, especially before a stressful event.  I also believe strongly in
making sure a horse is fully tanked up on hay for days before an event---it
doesn't seem like that would be closely related to hydration status, but it
is.  Very often I see horses tied to a trailer for hours at base camp
without a hay net while the rider is setting up everything else, checking
in, saying hi to friends, etc.  JMO, but there is NO higher priority before
a ride than keeping the horse eating as much hay as possible.  This isn't to
say that the horse will rely ONLY on hay the next day for energy, but hay
eaten the day(s) before a ride will strongly affect hydration and gut
motility over the weekend (another one of those endocrine things).  The more
dry matter eaten, the more water the horse will eat and the larger that
reservoir of fiber, water and other nutrients that'll be available the next
day when it's needed.

Seeya,

Susan Garlinghouse



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