How a Horse Stays Warm in Winter – Thermoregulation and Hypothermia in Horses

Settle down for a good read, folks!  We are digging into how a horse regulates his body temperature in winter to stay warm, and how you can spot hypothermia – a falling body temperature.  

Go straight to the good stuff:

What is thermoregulation?

Types of heat movement in horses. And people, too!

How does a horse regulate his body temperature?

When your horse’s temperature goes haywire in winter.

What happens to your horse as his temperature drops?

How do we measure this in horses?

What to do if your horse’s body temperature is falling below normal

Risk factors for hypothermia in horses.

How can we help our horses in cold weather with this process?

Things to consider helping your horse stay warm in the winter.

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What is thermoregulation? 

  • When your horse needs to change something about his body to return it to a normal temperature, this is thermoregulation.  It’s balance!  You know, similar to that elusive work-life thing.  
  • There are numerous forces at work within your horse, and all move towards bringing him back to homeostasis.  What’s homeostasis?  It’s the ability to remain normal on the inside, despite everything in the outside world going on.  Quite literally, it’s another balance, and thermoregulation helps to keep your horse there by moving heat around. 
horse in blanket standing in snow by the fence

Types of heat movement in horses.  And people, too!

  • Convection is when heat moves from your horse’s body by way of the air or water.  Think of it as heat loss as water or air move across your horse’s body. 
  • If your horse was to actually touch something, he would lose heat by conduction.  Tack, blankets, and your hands actively conduct heat from your horse’s body and they themselves become warmer.  
  • There are also infrared rays that are emitted by a horse, in a process called direct radiation.  This is heat transfer, without touching.  It’s dependent on the air temperature and usually happens when the air is below about 70°.
  • Evaporative cooling via sweat can account for 85% of a horse’s heat loss during intense exercise and sweat.  As the moisture in sweat evaporates into the air, heat goes with it. 
  • There’s one last way for horses to thermoregulate, and that’s with their breath. The proportion of heat loss can be quite low compared to other methods, but it’s there. 

How does a horse regulate his body temperature? 

  • Heat moves from warm things towards cold things.  True for horses, people, trains, trees, ovens, and just about everything.  This happens in summer and in winter.  Warmer temperatures in summer can hamper a horse recovering from exercise, and in winter, horses can lose too much heat to the environment.  
  • The environmental temperature, such as the air temp or wind chill, and your horse’s own body heat work together.  Your horse has to actively work to conserve heat in the winter as his body heat moves to warm up his surroundings.  
  • Horses and humans alike work to remain in a state of homeostasis.  When thinking about thermoregulation, this means a horse’s body temperature remains in a safe zone, usually between 99° and 101°.
  • If your horse starts to have a drop in temperature, his body naturally speeds up some internal chemical reactions to create more body heat.  This costs calories!  
  • Your horse might also increase his body heat by moving around.  If possible, your horse will move.  Horses also shiver to create the same effect, just as people shiver.  Exercise and movement and shivering create heat, and also requires calories.  
  • Horses are also experts at directing where their blood flow happens to keep their internal organs warm.  Legs, faces, and ears will have less blood flow to keep things running smoothly inside.  
  • When it comes to their coats, horses have a mechanism there, too.  Each hair follicle has a tiny muscle that can make the hair stand up.  This is called piloerection and is basically “goosebumps”.  Over large areas, this creates a fluffy coat that insulates your horse.  
  • As with many things horses and humans, older citizens have more trouble with thermoregulation.  Take this into account as you are designing your horse’s winter lifestyle.  
bay horse with a winter coat and lots of dried sweat marks

This guy sweat his butt off and may do better with a clip and blankets. 

When your horse’s temperature goes haywire in winter. 

  • The main concern is that your horse doesn’t develop hypothermia in winter.  This is when your horse’s internal body temperature drops below normal.  Luckily, this is rare!  
  • But it’s important to keep your eyes peeled.  And have a thermometer handy.  Just like hyperthermia (overheating), a drop in body temperature can be dangerous. 
  • Mild hypothermia occurs when a horse’s body temperature is between about 89° and 99°F.  
  • Moderate hypothermia is a body temperature of about 82° to 89°F.
  • Severe hypothermia happens when a horse’s temperature is below 82°F.
  • The lower a horse’s temperature becomes, the more danger he is in.  

What happens to your horse as his temperature drops?  

  • You might notice that your horse starts to be lethargic and sluggish.  He may not want to move, and he seems depressed.  
  • His heart and respiratory system will start to malfunction as hypothermia progresses.  He might experience some neurological issues, as well.  His liver and kidneys can shut down, and his gut will stop moving.  Horses may also develop problems clotting blood, which can cause excessive bleeding. 
     
Digitial thermometer

This is the best thing to have at the barn, all year long. A simple thermometer. 

How do we measure this in horses?

  • This is subject to a few concrete and measurable things, and a bit of guessing.  
  • The most reliable method is to take your horse’s temperature!  There’s no guessing here.  If you have that weird feeling in your gut warning you to be alert, continue to take his temperature over a few hours to track its progression.   
  • There are a few other ways to check if your horse is cold, but honestly, these are so subjective that they can’t be relied upon.  Feeling your horse’s ears and shoulder are relative to your own body heat.  Did you just get out of a car with the heat on full blast?  Your horse will feel cold!  If you have spent the past hour outside without gloves on, of course, your horse will feel warm. 
  • If you notice your horse shivering – his body is doing some work to get warm. BUT – how comfortable is he?  And is the shivering enough to increase his body temperature?  What time of day is it?  If he’s shivering in the afternoon, he will only continue to struggle overnight. Time to intervene. 

What to do if your horse’s body temperature is falling below normal: 

  • Start to track his vital signs and call your vet pronto!  Knowing his heart rate and respiratory rates and gum color are key pieces of information to log.  
  • Veterinary care is critical here, all hands on deck for this.  Don’t do any of these things without first talking to your vet. 
  • For mild cases, your horse will need to be passively warmed.  Move him into a shelter and out of any wind.  Use blankets to help him warm up.  He may need to be fully tarped to help contain warmth from head to hoof.  This will cover the area that blankets don’t reach.  
  • For moderate cases, it’s time to break out more tools.  Using heat lamps, warm water, heating pads and the like can bring up your horse’s temperature.  This, however, carries the risk of bringing blood into the extremities, away from the internal organs.  Burns are also possible if not done correctly. You will also have to manage a wet horse in cold weather.  Your vet should absolutely be involved by this point.
  • For more severe cases, your horse will need to be managed from the inside and outside.  Intravenous (IV) fluids are given, and there’s even a way to wash his internal cavity with warm fluids to help bring him into safety.  
  • For any of these situations, just returning to a normal temperature isn’t enough.  There needs to be continuous monitoring of organ function.  Heart problems, whole-body infections, and pneumonia are all possible.  

Risk factors for hypothermia in horses. 

  • Age is a big factor here!  Young horses and old horses are most at risk.  Add in some metabolic issues like PPID or thyroid problems and the risk is greater.  Any time there’s an underweight or malnourished horse, the risk is greater.  Injuries and infections can also complicate things.  

How can we help our horses in cold weather with this process?

  • Looking at some science about weather temperatures, this can give us guidelines for our own individual horses. 
  • The University of Main Cooperative Extension has found that there is a lower critical temperature (LCT) for horses.  It’s between 30° and 50°F.  
  • The LCT is just a number at which we need to start helping our horses maintain their body temps.  And by helping, I mean stuff we already do, just maybe modifying it a bit – shelter, food, blankets, clipping, etc.  
  • The LCT will vary from horse to horse and a horse’s hair coat.  For clipped hair or wet horses, this is usually around 60°F.  On the other end of the spectrum, a full winter coat may need help at 30°F.  Every horse will be different.  
gray horse with dinosaur mane and full body clip with saddle patch

This old man needs a clip to stay not sweating in the winter.  Go figure. 

  • But every horse has his own comfort levels! My horse, bred to live inside the Arctic Circle, can be fully clipped and sweating while standing around at 40°F.  Another favorite horse of mine needs a heavy blanket with his own fur coat at about 55°F.  
  • Factor in the wind chill, too.  Thank goodness for modern technology, weather apps have temps and wind chill temps listed.  Follow the wind chill temps!
  • Don’t think of the LCT as a die-hard number, just know that at some point, you need to alter your horse’s management to help him.  Take into account lots of things for your individual horse. 

Things to consider helping your horse stay warm in the winter. 

Blankets

  • It is true that blankets squash down a horse’s coat, with heavier blankets creating more squash.  This can prevent his hair from standing on end and making those warm air pockets.
  • Some horses need blankets anyway.  Any squish that is caused can be made up with a heavier fill or layering thinner sheets under a waterproof outer shell.
  • For young, old, underweight, or health-compromised horses, adding blankets is one part of helping him conserve calories and stay comfortable.  This is also a nice way to keep a horse dry during wet weather.

Shelter

  • The good thing about horses is that most understand if they are getting too cold, moving into a shelter that breaks the wind can help immensely.  We often gasp that a horse is outside in horrible weather when his shelter is right there!  But they know what’s up, usually.  
  • Sheds are also a nice place to have a water source, which may help your horse’s water stay cleaner than out in the elements.  Sheds can also have mats and bedding for some softer cushion than frozen winter ground.  You can also easily hang hay nets inside for slow feeding. 
red horse wearing a ski hat on his ears

It’s questionable if a beanie will keep your horse warm.  I say no, but it’s good for a photo op. 

Proper grooming for your horse’s natural oils. 

  • By now you know that my favorite soapbox is about a horse’s natural oils, AKA sebum. I usually harp about this as it relates to stains, using detergents on your horse (bad), and other grooming stuff.
  • BUT – those natural oils also help your horse stay relatively waterproof in bad weather.  A horse’s natural winter coat will shed most rain that lands on him.  The long hairs create a barrier, keeping warmth in and his skin dry.  Oils repel that water! 
  • There are, however, plenty of circumstances that a horse will get wet to the skin.  Sweat does this, as can a shorter winter coat, as can a horse without a lot of sebum.  Torrential downpours and non-stop weather are also capable of soaking a horse to the skin.  
  • Only you can decide what level of clipping and blanketing your horse needs, but all horses need those precious oils.  Avoiding detergents, dish soap, laundry products, and harsh shampoos is a good first step.  Also, spend extra time grooming.  Even more time than you think is necessary! Your curry comb routine is key.  

Is your horse’s diet adequate for helping him stay warm this winter?

  • For most horses, there are two things to think about – forage and omega fatty acids. 
  • Forage keeps your horse warm, and omega fatty acids help provide that shine-boosting fat to your horse’s life. 
  • As far as thermoregulation goes, adding forage is much better than adding a bagged feed.  Plain ol’ grass hay is best.  
  • Getting back to a bit of science here, let’s say you have guesstimated that your horse’s LCT is 40°F.  Below that temp, you need to do some extra stuff for him.  If forage is your choice, you can use the following formula to figure out the increase in hay to feed. 
very green timothy hay stacked in a barn

You can’t go wrong with hay to help your horse heat up.  Use slow feeders! 

  • For every 5°F drop below your horse’s LCT, feed one more pound of grass hay.  
  • The best way to do this is with slow feeding!  Hay nets or ground feeders are best.
  • Forage takes a long time to travel through your horse, and in the hindgut, those microbes living insider your horse ferment the snot out of it.  Heat is produced from this process!  
  • Increasing your horse’s bagged feed isn’t the best idea.  This puts a lot of concentrated and higher sugar value feeds into your horse at once.  These are also passed through quicker than hay.  Colic and laminitis are definite risks of changing a horse’s diet that quickly. 
  • Additionally, those bagged feeds don’t ferment and produce heat for hours!  Only hay does that, and adding a few pounds of hay via a slow feeder is much safer.  Make sure it’s the same type of hay he’s already eating.  
  • The absolute best thing you can do for your horse is talking to an Equine Nutritionist about your horse’s particular dietary needs.  

Checking your horse’s body weight on a regular basis. 

 

  • Our eyeballs are deceiving!  Using a weight tape is wildly easy and inexpensive, not to mention more reliable.  This allows you to track your horse’s condition over the winter.  

As with all things horses, they tend to do what they need to do.  And while the risk of hypothermia is low, winter is the time to pay extra attention.  You can help him regulate his own temperature to help prevent issues down the line.  

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