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Friday, May 17, 2013

Sweat patterns in horses

In the various discussions on hydration on this blog, I've mentioned a couple of "rules of thumb" that can be used when estimating dehydration in a horse. 

Here's some points that I posted here from a seminar at the 2012 AERC convention (and yes, I realize that I've harped and harped and harped on this subject for the last couple of weeks....)
  • Dehydration under 5% can't be accurately identified without blood analysis. 
  •  6-7% usually has some other associated problems
  • A 12% dehydrated horse is about to die. 
  • In school we were taught to determine dehydration by deciding whether the horse was mildly dehydrated (5%), moderately dehydrated (9%), or severely dehydrated (12%).  By taking the horse's weight in kilograms (~2.2 pounds per kilogram, I tend to use 400kg for the average arab that is 800-1000 pounds), and applying the % estimated dehydration, you can calculate the approximate amount of liters that the horse is deficient.  For example, a 5% dehydrated 400kg horse = 5%*400 = ~20 liters.  (3.8 liters per gallon, so 20L = 5 1/4 gallons of water) Thus, this horse needs to consume 5+ gallons over and above it's maintenance fluid requirement in order to rehydrate (FYI - average maintenance fluid requirement for adult mammals in in the neighborhood of 2-4ml/kg/hour, depending on size etc).
  • Average endurance horse is 5% dehydrated - regardless of whether its a 50 mile or a 100 mile. (Some interesting theories such as after 50 miles the thirst mechanisms finally catch up, or the coolness of the night/slowing down helps etc.)
  • Difference between tolerable dehydration and treatment is 2-3 gallons of water.  (it's really really easy to stuff 2-3 gallons of water into a mash with only a couple pounds of pellets!!!!)
  • The difference between tolerable dehydration and “about to die” is 8 gallons of water.
  • If you are a numbers person, using the math already discussed's how it works out: The moderately dehydrated horse (assume 9% and 400kg body weight) is missing 36 liters, or about 9 1/2 gallons of water.  The 12% (about to die) severely dehydrated horse is missing 48 liters or about 12 1/2 gallons of water.  
  • Trailering loss is 0.8 gal per hour, 1% dehydrated per 90 min travel. Thus, 8 hour trip produces a horse that is 5% dedicated upon arrival (6.25 gallons low). --> these numbers were given in Dr. Susan Garlinghouse's seminar. 

A very important point to notice above is that everything addressed above about a horse that is 5% dehydrated or more.
--> clinically dehydration isn't seen until a horse is approximately 5% dehydrated.  At this point they are considered "mildly" dehydrated. recently published an article on some recent research that looks at estimating fluid losses in horses BELOW that 5%!!!!  I think this is very exciting - because although I think all of us as horse people can make a good guess on whether our mounts are dehydrated or not, these types of tools and parameters provide us with even more information that we can use to evaluate our horses BEFORE they end up 5 gallons deficient. Because once they show clinical dehydration, you are only gallons of unconsumed water away to the level of dehdyration needing treatment. 

There is a reason that we hammer hydration hydration hydration in this sport.  The better we can educate ourselves, the better decisions we can make on the rides when it comes to our mounts. 

This research is very preliminary (hasn't even been printed yet - just epublished, but is going to come out as a future article in the Journal of Animal Physiology and Nutrition) and it's unclear how results may differ from the study population and conditions, but it's interesting to evaluate. 

Here is the link to the abstract in Pubmed

Here is a link to the article

Here is a link to the full article from the Journal

It has been added to the Mendeley Journal club (see sidebar of the blog). 

Additionally, here are some other articles that might interest you!  These are older papers (late '90s) but still good information if you want to learn more about the subject.

Comparison of three methods for estimation of exercise-related ion losses in the sweat of horses
- Pubmed

Sweating. Fluid and ion losses and replacement

Sweat fluid and ion losses in horses during training and competition in cool vs. hot ambient conditions: implications for ion supplementation.
- Pubmed 
- Article
- Added to journal club

PS. This was NOT my electrolyte post :)  Just a random article that I saw that I wanted to share with you.  


  1. I distinctly remember something you said in an older post about hydration -- that horses drink only if their mouths feel dry. And your suggestion (if I can call it that) was that in an endurance race that you NOT let your horse graze if you are close to a vet check or camp so that their mouth won't be wet. I've discussed with a few of my competitive friends. I had a habit of letting my horse graze often during a CTR/LD, sometimes making it a point of watching my GPS and letting him graze a bit every mile. My thought was that it would make sure he got some fiber/water in his system, but never thought it was actually preventing him from drinking. Do you still feel this way?

  2. so I believe the grazing thing was a side comment made about grass that is really wet or had a really high water content in it. The take home message is that you do not want to pre wet your horses mouth before they have a chance at a trough to drink their fill. if the horses thirst mechanism is telling them to drink it tends to get shut off early in the drinking process even before they have drank enough to meet there need. the main examples given for this scenario were people using water bottles to try and get there horses to drink or giving electrolytes and then rinsing. and yes I still feel this way :-) the grass in this area is never wet enough for me to feel like it poses a concern. just remember that first and then drinking has everything to do with what's going on in their brain and how their brain is interpreting there physiological conditions. yes this is a voice to text comment so feel free to laugh at my dumb spelling errors :-)


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