Hypothermia is a term that most of us are familiar with. But fewer people can describe exactly why it happens, or what effects a low body temperature has on the body. We’re going to explore what it means to suffer from hypothermia, but also when your pet is most at risk from suffering it. We also have some practical tips to keep your pet safe this winter, and especially during cold snaps.

Table of contents

What is hypothermia?

Hypothermia is the technical word for when an animal’s core body temperature drops below a normal level. In other words, when their ability to generate heat is less than the speed at which they are losing heat. 

Hypothermia can be primary, occurring due to prolonged exposure to cold environmental conditions, despite the body producing normal heat levels. But it can also be secondary, where the animal’s body is unable to produce its own heat effectively. Examples of this include illness, injury or certain medications.

The body is normally very good at keeping its temperature within a suitable reference range, but sometimes other factors can influence your pet’s thermoregulation.

Thermoregulation

Thermoregulation is how the body maintains a stable temperature despite being exposed to variable environmental conditions. The body must keep itself within a narrow, acceptable temperature range to maintain normal metabolism, enzyme activity and other biological processes. 

Being too hot (hyperthermic), or too cold (hypothermic) can cause serious problems. According to a 2021 research paper, ‘Temperatures above 45 °C can cause fatal brain injuries, while those below 27–29 °C can cause cardiac fibrillation, a progressive decrease in respiratory rate, and even death.’

Animals have two broad ways that they manage their body temperature –

Physiological 

These responses occur automatically without thought. Thermoreceptors in the body detect temperature levels and feed this back to the hypothalamus in the brain. This then causes changes which aim to generate heat through shivering, raising body hairs to trap a layer of warm air and vasoconstriction (narrowing of surface blood vessels), or dissipating heat which means getting rid of it by panting, sweating and vasodilation (widening of surface blood vessels).

Behavioural 

These are voluntary decisions that an animal makes in response to feeling too hot or too cold. These behaviours could include seeking shelter, curling up in a small ball to conserve body heat and huddling up with fellow pets when they are cold, or resting in the shade, bathing in cool water or lying stretched out on a cold tiled floor when too hot.

Through both physiological and behavioural responses, animals can keep their body temperature in the desired temperature range, which can vary slightly between species. 

Normal temperatures:

For most mammals, a temperature of around 37oC is normal, although our pets are a little warmer:

  • Dog – 38.3-39.2oC
  • Cat – 38.2-38.6oC
  • Rabbit – 38.5-40.0oC

How is heat lost from the body?

Excess heat can be lost from the body in the following ways –

  • Convection = heat moves from the body surface to air or water that is moving around the animal
  • Conduction = heat moves from the body to cooler objects or surfaces that are in contact with the animal’s skin
  • Radiation = heat is lost from the body in the form of infrared rays, moving from a region of high temperature to an area of lower temperature.
  • Evaporation = Moisture on the skin or in the respiratory tract evaporates into the air, causing a cooling effect 

Heat loss is important for animals when thermoregulating. Losing heat stops animals from becoming hyperthermic – too hot. However, when heat loss is excessive or occurs during cold temperatures it can cause the opposite problem, resulting in hypothermia.

An animal’s size, weight and body surface area will affect how rapidly it loses heat.  Small pets have higher surface-area-to-body-mass ratios compared to larger ones, which makes them particularly susceptible to heat loss.

Why might hypothermia occur?

There are several different reasons why hypothermia might occur. These include –

Cold environmental temperatures

Exposure to cold temperatures for an extended period could cause hypothermia. Being kept outside or living in an unsuitable outdoor enclosure during cold snaps could be problematic. There is a limit to what thermoregulation can achieve in these circumstances, and if these animals don’t have anywhere to warm up their body temperature will soon drop. Small and thin pets will be most at risk, but also elderly and very young animals. 

Getting wet

Most animals will be fine after a quick towel rub and somewhere warm to sit and dry off. But pets that remain wet, particularly on a cold day, will be at risk of hypothermia through evaporative heat loss. This risk is increased if the water is very cold and if your pet stops moving around and exercising. 

Anaesthesia and surgery

There are many ways in which animals could potentially suffer from hypothermia while anaesthetised and on the operating table. 

  • Breathing in cold, dry air directly into the lungs while intubated can reduce body temperature through evaporative heat loss.
  • Shaving areas of fur for surgery exposes more of the skin’s surface.
  • Cleaning surgical sites with antiseptic solutions and surgical spirit will lead to more evaporative heat loss.
  • Anaesthetic drugs may impact the brain’s thermoregulatory centre, including the ability to constrict blood flow from the body surface (peripheral vasodilation occurs)
  • Under anaesthetic, patients produce less body heat due to decreased muscular activity and metabolic rate.
  • Lying on a cold table surface can cause heat loss by conduction.
  • Having an open body cavity can lead to heat loss by radiation.

Hypothermia can delay anaesthetic recovery and lead to other complications such as heart arrhythmia (irregular heartbeat), low blood pressure, breathing issues and reduced blood clotting. As a result, vets and nurses take extra precautions to maintain their patients’ core temperature.

Blood loss

Blood is crucial to keeping your pet warm. Thermoregulation relies on good blood flow, which is how vasoconstriction and vasodilation work. If your pet has lost a significant quantity of blood they will go into shock and their body temperature will fall.

Illness

Many health conditions can affect an animal’s ability to regulate their body temperature. These include sepsis (blood infection), endocrine disorders such as severe hypothyroidism, an extreme allergic reaction, poisoning and end-stage heart failure. 

A note on the hypothermic spiral

When core body temperature falls below 34.4oC, that animal’s ability to thermoregulate becomes negatively affected. These animals may actually stop shivering and seeking heat at this point. Surface blood vessel dilation may occur, rather than vasoconstriction, leading to further heat loss. When core body temperature drops below 31.1oC any attempts to thermoregulate stop altogether. Once the temperature falls below 15oC, nerves and muscles are unable to function at all.

What are the symptoms of hypothermia?

Symptoms of hypothermia include –

  • Shivering – the body is attempting to raise its temperature through muscle movement. But remember the hypothermic spiral – if an animal becomes too cold it may stop shivering altogether.
  • Pale gums – a sign of vasoconstriction, blood being diverted back to major organs to help maintain core temperature 
  • Lethargy or confusion – the brain may start to become affected when an animal becomes too cold
  • Irregular heartbeat – in severely affected animals cardiac abnormalities may occur
  • Decreased breathing rate 
  • Collapse or loss of consciousness
  • Death

How can I protect my pet against hypothermia?

There are some simple steps you can take to protect your pets against hypothermia at home. These include – 

  • Taking extra care with very young, small, elderly or unwell animals. These pets should not be allowed outside for prolonged periods during cold weather spells. 
  • Ensure their sleeping area is somewhere warm and draught-free. Pets that normally sleep outside or in an outbuilding should have extra bedding and ideally a heat lamp. Preferably, they should be brought indoors during the winter months.
  • Invest in a good, waterproof coat for your dog, if they are in an at-risk category, or if they are very thin or hairless. You may want to skip a walk or two altogether during extremely cold snaps.
  • Avoid your dog taking prolonged swimming sessions during cold weather. While we recognise it is impossible to keep some breeds out of the water, you should limit their access during the winter months. Wet dogs will be more at risk from hypothermia, so keep sessions short, towel dry them immediately afterwards and let them dry off somewhere warm. If there is ice on the surface of the water, then it would be safest to save that swim for another day. 
  • Take extra care with small furries that live outside. You must check your rabbit or guinea pig’s enclosure is watertight and well-insulated. Provide them with extra bedding material and consider pet-safe heat pads. These animals will do much better in colder weather when they live with a companion or two, as they will be able to snuggle together for body warmth. If the weather is particularly cold, then you should consider moving their enclosure into a garage or shed. 
  • Seek veterinary help if you suspect your pet is suffering from hypothermia. There are some steps you should take at home or en route to the veterinary practice to improve the situation. This includes towel drying them if they are wet, covering them up with blankets and making sure they are in a warm house or car with the heating on. You must take care not to warm them up too quickly or burn them with anything like a hot water bottle.

A note on anaesthesia and surgery 

Vets and nurses take many steps to stop your pet’s body temperature from falling under anaesthetic. A warm room temperature, use of pet-safe heat pads, thick bedding and insulation (such as bubble wrapping or putting socks on extremities like paws) all help your pet to maintain their body temperature. Prolonged anaesthetic times are avoided where possible and there is constant monitoring of your pet’s body temperature, both during surgery and afterwards. This should give you some reassurance that your veterinary professionals are always taking sensible measures to ensure your pet’ safety. If you have any concerns, then speak to your practice for advice. 

Summary

Hypothermia can happen to any animal but some are at more risk than others, including small, elderly, young or sick pets. A drop in core body temperature can be caused in a variety of ways and leads to some serious health issues, so you must take steps during cold weather to protect your pets. 

If you have any concerns about your pet’s health or have any questions about how to manage your animal’s care in the winter months, then please contact your veterinary practice for advice. 

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