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Re: Re: The Edge



> I have a question (surprised?) or five, six, etc. :+)  Can a horse become
> dehydrated without losing any/much weight?

Not really---a gallon of water is roughly eight pounds, and for a horse to
become clinically dehydrated to a significant extent, he'd have to lose
about 5% of his body weight, or about 45 pounds (5.6 gallons) of strictly
water to get there.  Technically, I suppose you could have a horse that has
been losing alot of water, and hasn't lost alot of weight because for some
reason he was eating enough food to make up the difference, but that would
be *really* unlikely, especially without showing colic signs big time.


 Assuming most horses lose water
> weight (when they are weighing on the scales).....so reassure me again
that
> if my horse loses 6 pounds after going 50 miles, that it's safe to assume
> that he's not very dehydrated?

Rocky is fine, blondie. <g>


But if he loses say 40+ pounds, I otta be
> concerned?

Probably not, as a portion of that weight loss is also just "gut fill"---in
other words, he's just pooped out more than he's taken back in.  Especially
since you know your horses eat well during a ride.  If, on the other hand, I
saw 40+ pounds of weight loss in a horse that hadn't been eating or drinking
all day, and has obviously had a hard, hot day, yeah, I'd be concerned.  If
it were my horse, I'd stop/pull until the horse was eating and drinking
really well again and figure out what I needed to change to get the horse to
eat/drink at future rides.


 Have you found any correlation yet between weight loss and
> dehydration levels and/or enzyme levels?

We're looking, but still don't have absolute answers.  We need more data
points, which is why we need horses for the project at Tevis this summer.
You can get changes in all three of those parameters and they *might* be
directly related to each other, but they might not be as well.


 Tell me again how much water a
> 1,000 pound horse can lose before reaching a seriously dangerous stage?
Is > 4 to 6% still in an acceptable range?

The rule of thumb is that cellular function begins to be adversely affected
at around 3-4%, though you couldn't detect the changes without labwork.  You
won't see anything with the naked eye, no matter how good you are.  At 5%, a
good vet can see changes in CRT, skin tenting (maybe), though they won't be
severe, just some downward changes pretty typical for most horses after a
normal 50+ mile ride finished in decent condition.  At 8% dehydration,
they'll generally have a CRT of 2-3 seconds, poor skin tenting, dry tacky
gums, dryish poop (and so at greater risk of colic because everything's
getting jammed up in there) and usually hanging heart rate. A horse at 10%
dehydration is in serious, serious trouble, absolutely requiring immediate
veterinary intervention, and at 12%, the horse is close to imminent death.

 So far, the weight tapes I've used
> have been very accurate on the horses compared to the scales -- so you
> think it'd be worth trying to measure them before we leave for a ride, to
> see what they start out at before leaving home?

It would be interesting just to keep track, but since weight loss may
indicate just gut fill losses, rather than strictly fluid losses, I wouldn't
get too hung up in it.  You have to really look at the whole package---how
tucked up he's looking, mucous membranes, gut motility, heart rate, CRT,
attitude, way of going, etc.


 If my horses continue urinating
> like fire hoses, is that also a clue that I don't need to worry?  I have
> had people tell me that my horse pees so much he's going to dehydrate
> himself.  (stop laughing)  :+P

The *only* way you can get a healthy horse to pee himself dehydrated is if
you use diuretic drugs like furosemide (Lasix) to override the normal
adrenal-renal-baroreceptor systems that regulate that sort of thing.  There
are some diseases that can screw up fluid balance mechanisms, but you won't
be seeing those in a horse that's otherwise happily going on down the road.



> Another question.  Have any horses had higher cortisol levels than Rocky
> did after his near brush with death at Swanton? (when he fell off the
> mountain)

Yes, several.

Can cortisol levels rise from something like an injury or fall
> during a ride and then contribute to further metabolic problems later
> on? So that just because the horse may be sound and pass all veterinary
> parameters it's still a wise decision to pull the horse that day?


No, I really don't think so as long as you weren't stupid about it.
Cortisol levels rise in response to stress and they do things that help the
horse better handle that stress---increase blood glucose, lyse more body
fat, things like that.  Technically, however, cortisol also has the effect
of restricting the movement of glucose from the bloodstream into peripheral
tissue (like exercising muscles), and that might affect a horse that was
being pushed hard into glycogen depletion.  Cortisol also does slightly
override the above fluid retention mechanisms, so a horse is going to pee
more than he would strictly in response to renal function.  Enough to "pee
himself dehydrated", no.

So if something happened like a fall, and the horse was moving out sound but
you *know* he's got screaming cortisol levels, I wouldn't pull him just
based on that.  But I would ride more conservatively the rest of the day and
pay more attention to how the horse was doing, and pull at the first sign of
trouble.  And if the horse was one that already had a tying-up problem, or
was already dehydrated or peaky, or otherwise compromised, then yeah, I'd
pull.  Better safe than sorry and there will always be another ride, but
kidneys are forever.

Susan G



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