Over-electrolyting

[Sarah Ralston <ralston@AESOP.RUTGERS.EDU>]

Susan always makes my input so easy-she gives a full and detailed account
and then I can jump in with just a few corrections or "IMHO" additions!
Thanks again Susan!!

Susan wrote:
>  I happen to agree about not forcing
>electrolytes on a horse, in MOST cases, and certainly never on a dehydrated
>horse.  Electrolytes given to a horse that is NOT dehydrated are well
>absorbed, but sometimes it's hard to recognize the fine line between a horse
>that's dehydrated and one that isn't.  You can look at skin tenting,
>capillary refill, mucous membranes, etc and while this will certainly help
>identify the horse that is badly dehydrated, it's not an exact measure by
>any means.

Sarah Ralston replies:

AMEN! Skin pinch tests can either under or over estimate a horse's
hydration-get to know your horse's "normal" skin turgor on various spots on
his/her neck and shoulder-horses differ in skin elasticity, just like
people do

>The reason why you have to be careful about 'lyting a dehydrated horse is
>because electrolytes require water from/in the GI tract to be absorbed.  If
>the animal is dehydrated, and insufficient water available in the gut, then
>the electrolytes will essentially just sit there until sufficient water
>becomes available for absorption (and it's not an all-or-nothing thing, so
>degree of dehydration is a big factor).

Yes, and unfortunately while they are "sitting there" as a concentrated
salt solution, based on research I for my PhD (Too many years ago to
admit), they are causing abdominal pain-not necessarily colic per se but
just "I don't feel good". This is why, I am convinced, that so many horses
really fight being given their oral electrolyte doses-they associate the
dose syringe and force fed E-lytes with abdominal pain. If the "lytes made
them feel good-they'd beg for that dose!

> The body tries to compensate and
>deal with the problem as best it can, so it will scrounge up the necessary
>water by moving it from plasma volume (in other words, the blood) and into
>the gut so that electrolytes can then be absorbed back into the blood.  Sort
>of a robbing-peter-to-pay-paul thing.  If you have a horse that is already
>dehydrated, and perhaps on the edge of a metabolic crash, then it is very
>possible that by removing yet more plasma volume (even temporarily) from
>circulation, you can push the horse over the edge---which is totally
>opposite from what you were trying to do by 'lyting him in the first place!

Amen.

>Your friend is correct that electrolytes will create a thirst response, but
>it can sometimes be a day-late-and-a-dollar short.  The thirst response is
>not actually caused by the 'lytes themselves

Actually it is-there are two powerful stimuli for thirst-one is the plasma
volume reduction discussed below but the other is solute concentration or
osmotic pressure in the blood which is due in large part to it's
electrolyte concentrations-increase the sodium in the blood, you get a
drinking response even if plasma volume is unchanged. They are much more
sensitive to increased solutes than to decreased blood volume, which is why
most horses have to "learn" to drink at rides. Horse sweat is
hypertonic-which means it's electrolyte concetration is more concentrated
than the electrolytes in the blood. When horses sweat they lose
proportionately more electrolytes than water (people sweat is isotonic so
we don't have the same problems-another reason it's shaky to extrapolate
from human exercise physiology studies to equine athletes). This causes the
electrolytes in the blood to stay relatively the same or even decrease
during exercise, removing the most sensitive stimulus for thirst-its not
until a significant decrease in blood volume occurs later on that the
animal's volume receptors say "oops-there's a problem here-need to
replenish fluids". The salt appetite mentioned below kicks in even more
slowly. 

>it's caused by a loss in
>plasma volume (and thus blood pressure) which was essentially created or
>exacerbated by the electrolytes as described above.  When plasma volume
>drops, the kidneys release a particular cascade of hormones that do various
>things to restore blood pressure and increase plasma volume and one of these
>responses is the thirst response.  

The problem is that, based on work done recently by Laurie Lawrence at
Kentucky, it takes about 3-4 hours for the electrolyte thirst cue to really
do its job in stimulating increased water intake in a non-working horse
(ie: preloading before a ride). If you dose them the night before they
might drink more water over night (which is good if they are poor drinkers
to begin with) but most of it will end up on the stall floor if there were
no actual deficits being corrected and all those wonderful hormonal systems
regulating plasma volume and fluid volume will be geared toward excretion,
not conservation. So you give a second dose just before you start,
anticipating the first vet check to be 2 hours away-depending on
temperature, sweating etc, they might kick in just before the first check
if you are lucky, with your horse drinking like a fish just before you get
in (assuming there is a water source before the check). Unlucky? no water
until the check or they decide to kick in the thirst response just as you
are waiting in line for the P&R!

>Anyway, by the time the kidneys and hormones get around to triggering a
>thirst response, the horse drinks in reponse to that thirst, and water is
>absorbed back into plasma volume...well, you will eventually restore the
>lost plasma volume, but again, it may take awhile and if you have a horse on
>the edge of being in trouble, it may not be quick enough.  So forcing
>electrolytes to restore hydration is not a good strategy.

AGREED 100%-use them to replace electrolyte losses and to perhaps stimulate
intake BEFORE the horse becomes dehydrated!

>if you wait until a horse has has a good drink, and
>then electrolyte him, that's alot better---because the gut already contains
>sufficient water for the 'lytes to be absorbed, so water does not have to be
>moved from plasma volume into the gut.  But in *most* cases, 'lyting usually
>isn't necessary except under extreme circumstances. 

I don't entirely agree here. Judicious use, based on degree of sweating
(and beware dry climates!-Joe, remember how many east Coast horses got into
electrolyte trouble at the first ROC because you guys didn't see the sweat
rolling off them 'cause it evaporated so fast?) I feel is appropriate for
most 50 to 100 mile rides, especially in hot weather on the east coast. No,
electrolytes shouldn't be a major factor in a 25 mile competitive but rest
assured Fling, the sweat queen with a furry coat (Another long story why
I'm not going to clip her) will get her 2 ounces 4 hours before and another
dose during or after (depending on her sweat losses, water on trail,
attitude, etc) the easy Bunny Hop 25 next weekend, just because I know how
much she sweats and how sensitive she is to electrolyte losses. 

>Sodium is one mineral that animals will develop a near-immediate craving
for when they need it,
>unlike most other minerals.  So if a horse needs some electrolyte
>replacement, then just offering them to him in 'lyted water or whatever will
>usually be sufficient.

Yes, under normal training conditions this is absolutely true, but I don't
tend to trust my horse's nutritional wisdom in the heat of competition and
the sodium appetite can be over ridden by thirst-if you are really thirsty
after a hard workout do you reach for the pretzels or the beer first?

>In some cases, horses will do better if they're syringed with a bit during
>extreme heat, humidity and /or intensity of exercise, in addition to
>offering 'lytes in their water, mash, etc.  This can really vary widely and
>rather than rely on rules of thumb, it's best to experiment around a little
>with your horse to see what works.

This is essential-and also for regional differences-electrolytes are much
more important in hot, humid areas than in cool and/or dry region like the
Mountain and West regions

  In all circumstances, wait until the
>horse has had a drink and then syringe electrolytes in small, more frequents
>amounts rather than one big bolus.  Underelectrolyting by syringe is better
>during an endurance event than overelectrolyting---only because research by
>Carlson has demonstrated that even the best-drinking horse during hot
>conditions is incapable of totally replacing his fluid output during a
>50-mile endurance ride, 

Incapable or just didn't for that horse on that day? (have to admit I
haven't looked at the Carlson study for awhile)

>and so is experiencing some degree of dehydration.

But they are also experiencing electrolyte deficits-we are really walking a
fine line, because if the electrolyte deficits are severe enough they can
cause more drastic problems than simple dehydration. And actually the
Michigan study on multiple day rides reported that the horses actually
improved their hydration after the second and third days! Lots more work
needed here-it again points to the need to know your horse and the
conditions of the rides.

>Unless you're working closely with a vet, and/or know that your horse has
>just had a big tank of water and is metabolically all "A's", you need to be
>*very* careful and conservative about extra 'lyting.  Syringing is possible,
>and works well for many riders---just do it with awareness of what's going
>on in the horse's body and what the concerns are in what you're doing.

I agree.

>So if you have a horse that you know needs to drink, rather than
>electrolyting him in an effort to make him drink, try a few other tricks
>instead.  Ron Waltenspiel and his patented construction helmet will hold the
>water right up to the horse's mouth and based on Ron's record, I'll bet it
>works.  Try floating some hay or apple slices in his water, or try adding a
>flavoring agent, like a few handfuls of beet pulp to make it more palatable.

How about apple or grape juice? -I am serious-play with it at home to find
a flavor your horse really likes (mine seem partial to apple juice but
others like white grape juice!)-just avoid anything with caffeine or
chocolate in any form or fashion if you don't want to get caught on the
drug test! also rubbing their gums with just a little electrolyte soultion
(not squirting gobs of it down their parched throats) sometimes works too.

>While I don't like letting my horse play in water that he has to share,
>sometimes taking a bucket off to one side and letting him goof around a
>little will get him to finally settle down and slurp it up (I don't do this
>during conditioning rides, but if my horse really needs to drink, I'll do
>whatever it takes).  All these things, in addition to whatever existing
>thirst response he has without electrolytes, will encourage him to drink.
>If he doesn't, you're alot better off slowing down, using other methods of
>cooling (like sponging) to minimize fluid loss, and encouraging eating
>(especially a nice sloppy mash of beet pulp) until he does start to drink,
>rather than using electrolytes to force the thirst response into
overdrive.			

Thanks again, Susan!

Sarah, who is assiduously avoiding grading the stack of midterms on her
desk and dreaming of the trails instead and Fling (we are going to do WHAT?
in ten days? )


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