What’s up with anhidrosis?


Well, let’s start with what it is, a failure to sweat.  There is also hypohydrosis, which is the failure to sweat enough.  I have also heard this be called partial anhidrosis.  This is so critical in sport horses, as their TPR (temperature, pulse, and respirations) can go through the roof as they can’t cool off through normal sweating.  Many a horse has collapsed and even died as a result.


We are all stumped as to the cause of it, but we do know what can help it - in some cases.  For the most part, experts, Veterinarians, and researchers can agree on one thing - no one knows the reason for it, or the cure for it.   Generally speaking, it’s agreed that anhidrosis is some defect in the sweat glands.  It’s widely assumed that the sweat gland becomes desensitized to the chemical trigger of epinephrine.  In this case, increased concentrations of epinephrine which normally signal the sweat gland to start working are ignored.

We also know that there is no rhyme or reason for anhidrosis.  Age, gender, color, breed, and location don’t seem to be factors, although it’s reported that horses in hot and humid climates are likely to develop anhidrosis more often than more temperate climates.  


It’s also known that horses can develop this overnight, or over time.  It can also resolve itself, without explanation or logical reason.  (Nice to have such concrete info, right?)  In a nutshell, we can’t yet predict it or cure it. 




But we can manage it!  First we need to discuss how to spot it - or even the beginnings of it.  This is also where knowing your horse’s TPR comes into play - because with diminished sweating, the internal temperature of your horse can reach over 104 degrees and cause heat stress and stroke.  


Obviously, you will notice a horse with different or changing sweat patterns.  For example, the hind legs and neck may sweat, while under the saddle does not.  Or vice versa.  Or, you will notice no sweating at all. You will also notice lethargy, increased TPR values even at rest, dry itchy skin, hair loss (especially on the face) and increased recovery time after exercise.  


The strange thing about anhidrosis is that it can resolve itself, which is just as weird as it popping up out of the blue.  Some horses are fine the next season, or they become adjusted to the climate.  Others are normal for years and years and then develop anhidrosis, even without a climate change.  Some horses start to sweat again after a barn change in the same town.


How can you mange anhidrosis? 

There are a ton of ideas out there for management, and if you do the research, you will find a lot of contradictory information.  Much as anhidrosis has no rhyme or reason, the treatments don’t have any rhyme or reason, either.  What works for one horse doesn’t make a dent in others.  Most importantly, if you suspect anhidrosis, talk to your Veterinarian and start monitoring that TPR right away.  There are a few tests your Veterinarian can perform to confirm anhidrosis, one of them is a simple injection into the skin with epinephrine, which stimulates sweating.  If you horse doesn't sweat as a response to this, you are on the way to a diagnosis.  

Many riders and Grooms have had success with the supplement One A/C.  Others can manage with electrolytes, beer, methyl dopa, thyroid supplements, and even acupuncture.  



Maybe your horse will share with you? 


You will also need to monitor your horse’s environment.  Exercise in cooler parts of the day, which is often the morning.  Early morning.  Avoid turn out without amble shade and fresh water.  Set up a fan if you can, although a misting system is tons better as the gentle mist utilizes evaporative cooling and takes the place of sweat.


You may also have some success with a diet change, reducing the protein and carbs and increasing fat as the energy source.   This (and all management options) should be discussed with your Veterinarian.  


During exercise, be sure to monitor respirations and take lots of walk breaks.  Have a bucket with cold water and a sponge on the rail, or a spray bottle with water and rubbing alcohol close by.  Frequent dousing with the sponge, followed by the sweat scraper will help.  If you use the spray with alcohol, you may not need to scrape as the alcohol evaporates so quickly.  Hit under the neck and the major arteries of inside hind legs.  After the workout, implement major cooling off techniques.  Monitor your horse’s TPR closely, and check on him about 30 minutes later.  By then, his vitals should be back to normal, and if not, call your Veterinarian and do some more cooling off.


You can also consider some summertime clipping!


What has worked for your horse?