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  Discussion on Extreme reaction to heat/humidity compared to other horses.
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Posted on Friday, May 5, 2000 - 10:16 pm:

Hi there,

I have a spirited 16 year old, 1/2 QH, 1/2 Arab mare who is as healthy as a fiddle in all respects. She's glossy, wormed regularly, trimmed (hooves of iron), and exercised light-moderately 3X a week, all months of the year except January. I've had her since she was 3 and she's 16 now.

She does not react well to heat. There are 9 horses in the barn, and none of them experience the problems she does in hot, specifically hot and humid weather. When I boarded at other places, the other horses never experienced her sensitivity to heat either.

For example, on a very hot and humid day, even if she is in full fitness level, I'll take her for an easy trail ride with no cantering, or a basic schooling session with walking and trotting, and when I come back (after walking the last 10 minutes), as soon as she comes to a stop (not before) she begins to paw, sometimes violently, and has a glazed look in her eyes right before the onset of the pawing.

I have found that the only solution to stop her from reacting is to immediately hose her down for ten minutes from head to toe with cold water straight from the well. She has a complete look of relief when I do this and stands totally still even under ice cold water. If I don't hose her for long enough, she will get that glazed look in her eye, dopey body language, then start pawing again a few minutes later.

When she is moving she seems ok - it's when she comes to a stop that the heat/humidity seems to become too much for her.

This does not happen on ordinary days, only in the heat of the summer (with humidity). Again, the other horses don't do this and they are also ridden. It is not an evasion - if the next day is not humid, she's totally fine.

Last summer was terribly hot and humid nearly every day, and my final way of coping with this was to completely soak her from head to toe with water (avoiding the saddle) BEFORE I rode her. So I would start my ride on a soaking wet horse. She'd usually be dry or nearly dry by the time I brought her back, and in those cases she did not have any of her upset pawing and strange behaviour. I'd still soak her down again just in case.

Anyone else have a horse that seems supersensitive to very hot and humid days? What is this reaction she is getting - heat prostration? It's definitely not from overwork, I never work her more than to make her at most wet under the saddle and girth, rarely canter - it seems directly related to not being able to cool down. She only acts this way when she comes to a halt. It only happens when it's over 80 degrees farenheit, which happens a lot during our summers up here in Southern Ontario, Canada. I try to ride as early in the morning as possible but the heat's already oppressive by 10am when my ride is over. We go from -40 degrees celsius in the winter, to +40 degrees celsius in the summer.

Any other suggestions other than my full body hosings before and after the ride with cold water?

Other notes:
She always has full access to water in the stall and outside, a salt block in her stall, is fed a very basic ration of 3/4 of a milk bag holder of 12% sweet feed twice a day, Farnam Vita-Plus, basically free-choice hay, and finally, well-soaked beet pulp as a treat 3X per week when I visit.

She also goes into anaphylactic shock when given flu or rhino vaccines, and we were forced to discontinue giving those 2 vaccines years ago. Even the antihistamines eventually had no effect in reducing the reactions. Several minutes after the reaction, it would start with a cough or two. Soon, her gums would turn red-purple, she'd foam at the mouth, and go down. Tetanus shot is still given once a year and causes swollen neck, pain, and stovepipe legs even with antihistamine administration. Rabies vaccine has no apparent effect.

She seems to easily react or overreact to things - heat and vaccines - although she is a very easy keeper in all other respects and is incredibly willing to please. She is also extremely intelligent with tons of personality. Do a figure twice in a row and she starts anticipating immediately and trying to do it again if she thinks you are about to ask her. When I used to show, I had to do dressage tests backwards and all mixed up or else she'd have it memorized immediately. These nerves, I'm sure, add to her tendency to sensitivity. Despite her spiritedness, I still ride her in a soft KK french snaffle. She has excellent care and no vices.

Erin.

Posted on Saturday, May 6, 2000 - 8:12 am:

Hello Erin,
On those hot humid days during the ride does she sweat normally?
DrO

Posted on Wednesday, May 10, 2000 - 9:49 pm:

I already replied to this a couple of days ago, but it doesn't appear to have shown up.

Yes, she does seem to sweat normally on the hot, humid days. I don't think it's enough, though, because it isn't stopping her from overheating.

I notice that when she gets these pawing reactions, her veins in her skin still look distended like right after she comes out of trotting or other more vigorous exercise...even though she's been walking easily for at least ten minutes and often much longer. The next day she could do more work, and yet be totally fine.

Maybe her heat tolerance is just a lot lower than that of other horses. I know there's a formula you can use to calculate if the heat X humidity is too much for you to safely ride the horse, and perhaps for her the bar is lower.

I still wonder *why* her body would be that way, though...what, physiologically, makes her less heat/humidity tolerant. And does her high-blowing, excitable temperment exacerbate the problem.

Erin.

Posted on Thursday, May 11, 2000 - 10:59 am:

Right,
I thoink she is extra sensitive to the heat, I see no reason in your post to suspect anything other than a mild anhyDrOsis. However a good physical exam during one of the episodes including a complete laboratory work up might turn up something.

Is this worsening as she gets older? If it is anhyDrOsis, the stress of the bad episodes may make the condition worse over time so you need to learn to be able to judge safe days and bad days. See, The Horseman's Advisor: Equine Diseases: Lameness: Weakness, Exhaustion, and Overheating for the article on overheating and anhyDrOsis for the particulars.
DrO

Posted on Thursday, May 11, 2000 - 12:46 pm:

Dr O - I know that there are folks who believe that adding electrolytes will prevent anhyDrOsis, or at least minimize this. Does this belief come from studies or just anecdotal experience?

Posted on Friday, May 12, 2000 - 7:19 am:

Just anecdotal experience but not without merit from a logical standpoint. The judicial use of electrolytes might reduce heat stress and slow the onset. See the article on electrolytes and heat for some recommendations.
DrO
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