Anhidrosis in Horses (Non-Sweating or Dry Coat)
- What Causes Anhidrosis in Horses?
- Signs and Symptoms of Anhidrosis in Horses
- Diagnosing Anhidrosis
- Management and Treatment of Anhidrosis in Horses
- Tips to Help Keep Anhidrotic Horses Cool
- Key Takeaways
Reviewed By: Joan Maree Hinken DVM, CVA, CVSMT | Updated June 2, 2025
Anhidrosis is the decreased ability or complete loss of ability to sweat. Horses suffering from anhidrosis are often called “non-sweaters” or referred to as having “dry coat.”
Horses rely on sweating to thermoregulate and maintain a consistent internal temperature. They lose about 65 to 70% of their body heat through sweating and the evaporation of sweat. Not being able to produce an adequate amount of sweat can put your horse at risk of overheating (hyperthermia) or heat stroke.
What Causes Anhidrosis in Horses?
The underlying cause of anhidrosis remains unclear. Experts believe either something is wrong on the stimulation end (such as with the neurotransmitter adrenaline) or something is wrong on the receptor end (such as decreased numbers of receptors or decreased sensitivity of these receptors).
Some theories suggest that anhidrosis could be caused by an overstimulation of the sweat glands, which can be put into overdrive during the hottest times of the year and may essentially start to shut down.
Any horse can develop anhidrosis, no matter their age, gender, color, or breed. However, horses that live in hot, humid environments are more likely to be affected. Being born or raised in a warm climate does not give a horse any advantage over not developing the condition than one brought up in a colder climate.
Areas with high humidity can further reduce the amount of sweat that will evaporate, hence creating a more serious challenge for cooling your horse down. Oftentimes, a big change in environment (like horses traveling to Florida for the winter) can suddenly trigger non-sweating. Anhidrosis can also develop gradually over time and in varying degrees of severity.
Video on Equine Anhidrosis
Watch this Ask the Vet video on equine anhidrosis to learn how one horse owner tried to promote healthy sweating by giving their horse a certain drink.
SARAH: "I have a horse that was diagnosed with anhidrosis. Aside from medication, is there anything I can do to help him? I once saw a horse like that at a barn I was at before, and since medication wouldn't help him much, the owner decided to start giving him half a beer every morning to help him sweat. Apparently it worked, but is that a good idea?"
What do you think?
DR LYDIA GRAY: Um. Can I answer the first part...
SARAH: Yeah.
DR LYDIA GRAY: ...the last part first?
SARAH: Yeah, let's do it.
DR LYDIA GRAY: A lot of people give their horse beer, and specifically Guinness beer...a dark beer.
SARAH: It's a popular choice.
DR LYDIA GRAY: for this condition. And we should say, anhidrosis is the complete or partial loss of the ability to sweat in response to stimulation. So, when it gets hot and you think, "this horse should be sweating, because I've been working him" or it's just 100 in the shade and he's not sweating - that's anhidrosis.
SARAH: Now, some people would think, "Oh you don't sweat. That means you don't stink. That means you don't need deodorant," and they think it's a good thing. For horses it's not a good thing.
DR LYDIA GRAY: No.
SARAH: Can you tell us why?
DR LYDIA GRAY: When I look these up - cause this one got to the top of the list very quickly.
SARAH: Very quickly. Like 3,000 votes quick. This was a popular one.
DR LYDIA GRAY: So I knew right away I was going to have to answer this one. I looked up the species that sweat, because not every species sweats, right? Elephants, bats, sloths, lemurs, beavers, and primates. I can find no relationship between those animals.
SARAH: This is surprising.
DR LYDIA GRAY: But the point is sweat, like you were saying.
SARAH: Oh, could you imagine a sweaty bat? That's worse than just a bat is a sweaty bat.
DR LYDIA GRAY: A sweaty bat?
SARAH: Yeah, that's not good! That's not good at all.
DR LYDIA GRAY: These are funny. It's a funny list. But it's to cool you off. Your core body temperature gets warm, and then there are signals in your brain and throughout the body that release sweat from glands, and then the evaporation of that sweat, that liquid, is what cools your body off and maintains your temperature. The species that don't do that have to pant, like a dog, or wallow in mud, like a pig. They have other ways to cool their core body temperature off.
SARAH: Deodorant is looking pretty good right about now.
DR LYDIA GRAY: Yeah.
SARAH: You don't want to go around panting.
DR LYDIA GRAY: Or wallowing in the mud.
SARAH: Some of us do anyway.
DR LYDIA GRAY: The medication - there's not a medication for this, because we don't know why horses lose their ability to sweat. And it could happen at any age, breed, gender - there doesn't seem to be any sort of predilecetion or predisposition.
It does happen when a horse comes from a northern climate - say Massachusetts where we are - to Florida where it's hot and humid, and they suddenly lose their ability to sweat. Some of the advice is to allow your horse to acclimate to a new environment gradually. Make sure they're conditioned before you get there. If you're going to provide a supplement, not a medication, for this condition, then you want to have it on board before they start getting those signals to sweat. I don't normally mention a supplement, but there is one - it's called One AC - that has some really good research on it. It was done in Florida. It contains things like tyrosine, which is an amino acid, some B-vitamins, cobalt, niacin, and other things, and it has been shown to help horses sweat.
Beer has not been shown through research to help horses sweat, but anecdotally you hear about it. So I felt like I had to bring some today.
SARAH: Ok. Can you explain the difference - cause I think this is something, it's a subtlety that if you don't work at SmartPak, I think a lot of people just don't think about - the difference between a medication and a supplement.
DR LYDIA GRAY: Sure, so when we talk about a medication that's an FDA-approved prescription medication that is approved for use in the species. Here it's the horse. So there's been extensive research proving safety and efficacy. Millions of dollars, 7-10 years. It's a big deal. So when you see a Prascend, a GastroGard, something like that, that's got years and years and lots of dollars behind it. That's why we call them big pharma.
Signs and Symptoms of Anhidrosis in Horses
- A lack of sweat during or after exercise, or in warm weather. Some horses may sweat very lightly or just in patches. For example, at times when your horse should be lathered, such as during a summer afternoon ride when all other horses are sweating, they may only be a little damp under their tack.
- Labored breathing with shallow, rapid breaths and flaring nostrils. The horse will be trying as hard as he can to cool himself down by releasing heat. They will have an elevated respiratory rate for an extended period after exercise, usually for longer than 30 minutes. Their internal body temperature could reach as high as 104° Fahrenheit (the normal range is 99.5 to 100.5° F).
- A poor-quality coat with dry or flaky patches of skin and loose or thinning hair (especially on the forehead).
- Poor performance or a decline in their performance. They may be lethargic and become quickly and easily exhausted during training, which could limit their potential career.
- Not drinking as much water as usual and/or a loss of appetite.
Diagnosing Anhidrosis
If you suspect your horse isn’t sweating properly, call your veterinarian so they can examine your horse and rule out any other conditions with similar signs. Your vet will perform a physical exam and run diagnostic tests through injections that stimulate the sweat glands (with epinephrine or terbutaline). They will then measure the amount of sweat produced. Blood may also be taken so your veterinarian can measure your horse’s electrolyte levels.
Management and Treatment of Anhidrosis in Horses
While it may never completely resolve, there are options that may help manage the symptoms of anhidrosis. A few options that veterinarians, horse owners, and barn managers have seen success with include:
- vitamin, electrolyte, and salt supplements to support healthy sweating
- herbal remedies
- acupuncture treatment programs
- thyroid hormones
- giving your horse a dark beer
There is no one-and-done treatment for all affected horses - some options may be successful for one horse but ineffective on his barn mate. Some horses with anhidrosis regain the ability to sweat when moved from the hot, humid climate to a cooler, drier one, yet others don't.
Supplements That May Support Healthy Sweating
- Electrolytes such as chloride, sodium, potassium, calcium, magnesium, and other minerals are components of normal sweat and play an important role in nerve and muscle function. Even though an anhidrotic horse may not be losing minerals through sweat, they may still have abnormalities in their electrolyte levels (found through blood tests).
- Salt found in electrolytes will also encourage your horse to drink and help to maintain proper hydration levels. Adding an electrolyte supplement to your horse’s daily diet may help support their ability to sweat normally and promote overall well-being.
- Many sweat-promoting supplements are formulated to include l-tyrosine, an amino acid that is a building block of brain chemicals (neurotransmitters) and supports the proper function of the thyroid, adrenal, and pituitary glands.
- Vitamins E and C (known as tocopherol and ascorbic acid respectively) are antioxidants that support and protect the body from the oxidative stress of exercise, travel, and illness.
- Vitamin B3 (niacin) is also a key component in many formulas for its cell-protecting effects and role in energy production.
- Feeding a horse with anhidrosis a low sugar diet may be a good option if a veterinarian determines the root of the issue to be stress-related.
Each supplement has its own recommendations for how and when to start your horse on the product. This may involve giving the supplement before the hot season begins and reducing their workload for a few weeks when getting started. Remember to consult with your veterinarian before starting a product to ensure it’s the right one for your unique horse and the specific issue being addressed.
Tips to Help Keep Anhidrotic Horses Cool
- When bringing your horse to a hot, humid climate, allow him to acclimate with 10-14 days of turnout and light work before returning to regular training and showing.
- Get your horse "legged up" or conditioned with interval work or distance riding before the hot months so you don't have to work on basic fitness then.
- Work your horse during the cooler parts of the day, usually in the morning or evening.
- Avoid turning your horse out during the hotter parts of the day when the sun is strong, and make sure they always have a shaded area and plenty of water. If night turnout is available to your horse, it may be a good option to consider.
- Observe your horse closely during exercise for signs of overheating, such as rapid breathing or heart rate, and fatigue.
- Cool your horse off with water as cold as he will tolerate and quickly scrape it off. Keep reapplying and scraping until his temperature has returned to normal.
- Provide cool air with good barn ventilation and fans or misters.
Key Takeaways
Anhidrosis is a serious condition that requires changes in your horse’s daily management. Your veterinarian is your best resource for diagnosing anhidrosis and should be consulted before beginning any treatment plan. You may need to adjust your expectations of your horse’s ability to perform and their potential career. With early attention to the signs of non-sweating and careful management, you can keep your horse comfortable and prevent overheating.