Equine Thermoregulation and Hypothermia in Horses

What is Thermoregulation?

• When your horse needs to adjust their body 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, all of which help restore homeostasis. What’s homeostasis? It’s the ability to remain normal on the inside, despite everything going on in the outside world. It’s another balance, and thermoregulation helps to keep your horse there by moving heat around and preventing further heat loss in the cold, and additional heat gain in the heat.

• Hypothermia in horses happens when their body temperature cools below normal. This is an emergency.

Heat Loss Mechanisms in Horses

• As a horse works towards homeostasis, five major heat-loss mechanisms are at work.

• 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 moves across your horse’s body.

• If your horse were actually to touch something, they would lose heat by conduction. Tack, blankets, and your hands actively conduct heat from your horse’s body, and they, in turn, 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 depends on air temperature and usually occurs when the air is below about 70°F.

• Evaporative cooling via sweating can account for 85% of a horse’s heat loss during intense exercise. As moisture in sweat evaporates into the air, heat is carried along with it.

• There’s one last way for horses to thermoregulate, and that’s with their breath. The heat loss can be quite low compared to other methods, but it’s still there.

Read more about loss of heat in the warm weather in this riveting article about heatstroke and thermoregulation in the summer!

How do Horses Regulate Their Body Temperature?

• Heat moves from warm things towards cold things. This movement is 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 months, horses can lose too much heat to the environment.

• The environmental temperature, such as the air temperature or wind chill, and your horse’s own body heat work together. Your horse has to actively work to conserve heat in winter, as their body heat is directed toward warming the surroundings.

• Equines and humans alike work to maintain homeostasis. When thinking about thermoregulation, this means a horse’s body temperature remains in a safe zone, usually between 99°F and 101°F.

• If your horse experiences a dangerous drop in temperature, their body naturally speeds up certain internal chemical reactions to generate more heat. This costs calories!

• Your horse might also increase their body heat by moving around. Equines also shiver to create the same effect, just as people shiver. Exercise, movement, and shivering generate heat and also require calories.

• Horses are also experts at directing blood flow to keep their internal organs warm. Legs, faces, and ears will have less blood flow to keep things running smoothly inside. You may feel cold extremities, but your horse’s core temperature may still be within a safe range. This measurement is subjective and unreliable.

• When it comes to their coats, they have a warming 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. Wet fur hinders this ability, and in muddy conditions, mud can as well.

• As with many things equine and human, older citizens and those with poor body condition have more trouble with heat production and thermoregulation. Take this into account as you are designing your horse’s winter lifestyle.

Hypothermia Ranges

• The primary 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 essential to keep your eyes peeled. And have a thermometer handy. Just as hyperthermia (overheating) can be dangerous, a drop in body temperature can be hazardous.

• Mild hypothermia occurs when a horse’s body temperature is between about 89°F and 99°F.

• Moderate hypothermia is a body temperature between 82°F and 89°F.

• Severe hypothermia happens when a horse’s temperature is below 82°F.

• The lower a horse’s temperature becomes, the more danger they are in.

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

Symptoms of Hypothermia in Horses

• Any new, abnormal, or weird behaviors always warrant attention. Some common signs indicating the onset of hypothermia include:

• Shivering. This is an involuntary reaction to cold, wet conditions that gradually lowers the average body temperature.

• Lethargy and depression. You may notice lower energy and less movement.

• Not eating or drinking. This is quite the red flag, and should be thoroughly investigated.

• Cold extremities and chilly skin. You may feel like the legs and skin are cold. This feeling is a subjective measurement, and you can’t rely on this alone. If you have just exited your warm car with the heat at “surface of the sun” and you touch your horse, they will seem cold. If your hands are turning blue and you can’t feel anything below your elbows, your equine buddy may feel warm. In either situation, you can be wrong.

• Unusual posture. Perhaps your horse’s shape is hunched, and they have their tail tucked tightly in an effort to conserve heat.

• Clumsy movement. Ataxia is the technical term for uncoordinated movement and indicates neurological problems. It is a dangerous development in horses and can lead to hypothermia.

Severe signs

• If you notice any of these things, your horse has serious health concerns with potentially devastating consequences. Their heart and respiratory system will start to malfunction as hypothermia progresses. They might also experience some neurological issues. The liver and kidneys can shut down, and the gut will stop moving. Equines may also develop blood-clotting problems, leading to excessive bleeding.

• • Low rectal temperature. This is the easiest way to track your horse’s thermoregulation. Temps below 99°F (37.2°C) need to be monitored every few minutes to see if they’re rising or falling. Also, call your veterinarian pronto.
  • Slower heart rate. Irregular beats or a slower-than-regular pulse indicate danger.
  • White or blue gums. Any color besides pale pink indicated a circulatory problem, but especially blue or white gums.
  • Enlarged pupils. The eyes may appear to be larger.
  • Being “down” or collapsing. Hypothermia in horses may create the inability to stand.
  • Miscellaneous neurological signs. You may notice confusion, muscle weakness, stumbling, or falling.

Frostbite

• Horses can develop frostbite, and it’s usually noticed after the tips of the ears fall off. Being covered with hair hinders your ability to see the skin and any damage.

• You may also find frostbite on the penis, sheath, or legs. The tissue dies and needs veterinary care, such as antibiotics and pain medications. Low temperatures and wet conditions can cause frostbite, though it’s rare.

• For foals, seniors, and hard keepers, they have a higher risk of frostbite compared to a healthy adult horse. However, rain, mud, and sudden weather changes can pose a danger to even the healthiest herd members.

Read more about frostbite here.

Measuring Hypothermia in Horses

• If you even remotely suspect your horse is “off,” take their vital signs. This includes pulse, respiratory rate, temperature, gum color, and digital pulses. When you know your horse’s normal range, you are alerted to abnormal conditions before they ever show you a sign of trouble.

• Check in with your vet and continue monitoring their vitals, noting any trends. Obviously, if they stray outside of the usual, talk to your vet again.

• There are a few other ways to check whether your horse is cold, but honestly, they are so subjective that you can’t rely on them. Feeling your horse’s ears and shoulder is relative to your own body heat. Did you 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, your horse will, of course, feel warm.

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

What to Do if You Suspect Hypothermia

• If you notice your horse shivering, their body is working to stay warm. This shaking is a normal reaction to cold environmental conditions, but it’s not comfortable, and it’s the first sign of trouble. Also, ask yourself if shivering is enough and how long your horse can sustain it? It’s better to intervene before shivering turns into permanent tissue damage.

• Start to track their vital signs and call your vet pronto!

• 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 passive warming. Move them into a dry shelter out of the wind. Use blankets to help them warm up. Your vet may want you to cover them with a tarp from ear to tail, top to bottom.

• For moderate cases, it’s time to break out more tools with your vet. Using heat lamps, warm water, heating pads, and similar devices can raise 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.

• For more severe cases, your horse needs management from the inside and outside. Warm Intravenous (IV) fluids are usually given, and there’s even a way to lavage (wash) the internal cavity with warm fluids to help bring their temps up safely.

• For any of these situations, just returning to a normal temperature isn’t enough. Continuous monitoring of organ function is required. Heart problems, whole-body infections, and pneumonia are all possible.

Risk factors for hypothermia in horses

• Age is a significant factor here! Young 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.

Your Horse’s Lower Critical Temperature (LCT)

• Looking at scientific research on weather and temperature, we can develop guidelines for our individual horses.

• The University of Maine Cooperative Extension has identified a lower critical temperature (LCT). It’s between 30° and 40°F, or roughly 0°C to 5°C.

• The LCT is just a number at which we need to start helping them maintain their body temperatures. And by helping, I mean stuff we already do, just maybe modifying it a bit – shelter, food, blankets, clipping, etc.

• The LCT will vary. 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.

• But every horse has their 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, such as weather apps that list temperatures and wind chill. Follow the wind chill temps!

• Don’t think of the LCT as a hard-and-fast number. At some point, you’ll need to adjust your horse’s management to help them.

• Read more about LCT here.

This older man needs a clip to prevent wild sweating in the winter.  Go figure. 

How to Prevent Hypothermia in Horses

There are many things you can do! It’s not about adding one thing into the equation, it’s more about adjusting all manner of care to prevent problems.

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

Feeding and nutrition

• 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 and calories to your horse’s life.

• As the pasture dries up, you may find that supplementing your horse’s diet with omega fatty acids is necessary. Corn oil is not the best option for horses, but flaxseed and fish oils are.

• 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 first choice, you can estimate how much to add.

• Most horses need about 2-3% more calories for every Celsius degree below their LCT, which is roughly 2-3% more calories per 2°F.

• You don’t need to calculate all of this every night, especially if you blanket and have shelters that your horse uses. You can bank on an additional 30% more forage for most horses in the winter. Keep tabs on your horse’s weight to ensure they are getting enough without overeating.

Slow feeding

• 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. These feeds may add unnecessary sugars and starches, pass through your horse quickly, and increase the risk of laminitis in some horses.

• 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 they’re already eating and acclimated to.

• The absolute best thing you can do for your horse is talking to an Equine Nutritionist about your horse’s particular dietary needs.

Blankets

• Blankets indeed squash down a horse’s coat, with heavier blankets creating more squash. This squishing can prevent their hair from standing on end and making those warm air pockets. But they provide waterproofing and windproofing, and the fill makes up for the squished hair.

• Some horses need blankets anyway. Any squish is remedied with a heavier fill or by layering thinner sheets under a waterproof outer shell.

• For young, old, underweight, or health-compromised horses, adding blankets is one way to help them conserve calories and stay comfortable. Blankets are also a good way to keep a horse dry in 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 when a horse is outside in horrible weather, even though their shelter is right there! But they know what’s up, usually.

• Ensure your horse feels safe enough to use a shelter in a herd setting. They may need it, but won’t use it because they will be forced out or cornered, in which case it’s time to make some herd adjustments.

• 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 a softer cushion than frozen winter ground. You can also easily hang hay nets inside to slow feed and tempt them to stay out of the wind.

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.

• 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 them. The long hairs create a barrier, keeping warmth in and his skin dry. Oils repel that water!

• There are, however, plenty of circumstances in which 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 equine partner 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.

As with all things equine, 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 them regulate their own temperature to help prevent issues down the line.