Re: electrolyte supplementation

[Michael I Lindinger <mlinding@uoguelph.ca>]

On Fri, 17 Apr 1998, CMKSAGEHIL wrote:

> In a message dated 98-04-17 09:00:41 EDT, mlinding@uoguelph.ca writes:
> 
> << One needs to differentiate between the concept of 'conservation' versus
>  what what is available to be lost (in either urine or sweat. If the
>  electrolyte is not available, it cannot be lost at adequate rates to
>  produce an optimum sweating rate for effective thermoregulatory cooling of
>  the exercising horse.>>
> 
> With a good roughage fill in the gut, good parameters throughout competition
> regarding gut sounds, hydration, etc., and on the occasions we have done
> bloodwork, not a lot of depletion of electrolytes post-ride, I would have to
> assume that my horses have adequate amounts available to be lost.  The fact
> that I do not force supplement electrolytes would lead me to believe that a)
> they get plenty from feed and free-choice electrolyte, or b) conservation DOES
> work, or most likely c) both of the above.

I will comment on the preceding paragraph. One cannot tell from
measurement of plasma electrolytes alone if the horse is electrolyte
depleted. It is also necessary to measure the change in plasma volume
(using plasma protein concentration for example) which gives one an idea
of the decrease in the extracellular fluid volume - the volume of fluid
outside of the cells. One also need to know the decrease in body weight of
the horse. the difference between the decrease in body weight and decrease
in extracellular fluid volume represents the decrease in water inside the
cells. When one then applies the changes in plasma electrolyte
concentrations to the fluid losses, the electrolyte losses are very
appreciable -- we are talking cup fulls of salt in 50 to 100 mile
endurance rides. I refer you to papers by G. Ecker and M. Lindinger in
Equine Veterinary Journal in 1995 and 1996.

Thus, examination of plasma electrolytes alone CANNOT allow you to
determine electrolyte and dehydration status.

>  
>  <<You noted, correctly (as I pointed out yesterday) that sweat electrolyte
>  concentrations may decrease in horses as they become conditioned. This is
>  primarily ascribed to the production of a MORE DILUTE sweat, i.e. more
>  water with the same amount of electrolytes. Therefore electrolytes still
>  are not conserved.>>
> 
> You are presuming that they are sweating 10 times as much, since the sweat is
> 1/10 the concentration.  I'm not sure I buy that.  Certainly fit horses sweat,
> and need to sweat, but unfit horses also sweat copious amounts--perhaps even
> more, as they are not as good at thermoregulation and often have more
> insulating fat making it more difficult to get rid of body heat.  If the
> VOLUME is the same, then the more dilute sweat most certainly represents a
> lower electrolyte loss!
>  
Your presumption here is incorrect. They are NOT sweating 10 times as
much.
For the same amount of sweat they secrete 10 times more salts than do
humans. This is well documented in the literature - 20 years from a
dozen different investigators.

>  <<When you think about it, it does not make good sense to try to conserve
>  electrolytes at the skin, because this will impair the ability of the
>  horse to sweat and produce related heat stress problems. What may appear
>  as 'conservation' may be an inabilty to provide the sweat because the
>  water and electrolyte reserve is not adequate.>>
> 
> It makes good sense to conserve electrolytes everywhere possible.  As long as
> the sweat VOLUME is adequate, there should be no impairment whatsoever to
> thermoregulation.
>  
It may make good sense to conserve electrolytes from an electrolyte
balance point of view, but NOT from a thermoregulation point of view. It
appears that the need for thermoregulatory cooling is predominant, as it
should be. electrolytes can always be regained from the feed (at the
least).

Mike Lindinger