Hyperthermia – overheating

With their dense fur, healthy rabbits in a sheltered environment are tolerant of low temperatures, but cannot tolerate damp or draughty conditions. On the other hand, they cannot pant effectively and don’t sweat, therefore are susceptible to overheating. Unfortunately, even with treatment, the prognosis for rabbits with hyperthermia is guarded to poor.

Rabbits can regulate their body temeprature to a degree using their ears; increasing blood flow (vasodilation) to the ears enables heat to be lost to the environment. However, unlike other animals like dogs, rabbits can’t pant to regulate their body temperature. Therefore they are very susceptible to their body overheating, or hyperthermia. Mouth breathing in the rabbit is extremely serious and a life-threatening sign.

If the rabbit’s body temperature rises over 40°C, they are very likely to suffer from hyperthermia.

Hyperthermia can have effects on many parts of the body, including the nervous and respiratory systems, the heart, digestive tract and kidneys.

There are several risk factors for hyperthermia in rabbits:

  • Excessive heating of the rabbit’s environment, e.g. on a hot sunny day (>28°C ambient temperature) without shade and drinking water. Direct sunlight, poor ventilation, high humidity and dehydration all predispose to hyperthermia.
  • Drugs including some anaesthetics can affect the rabbit’s ability to regulate its body temperature although this normal results in hypothermia.
  • Excessive exercise, particularly if it involves stress, e.g. chasing a rabbit to capture and handle it; exertion creates body heat.
  • Stress and anxiety due to other causes, e.g. confinement in a vehicle or small carrying box or being in the presence of predators.
  • Heavily pregnant does, obesity, elderly rabbits, a thick hair coat, and underlying disease, e.g. heart disease or infection, are also all predisposing factors.

Several of these factors may combine in one instance.

Clinical signs may include:

  • Extremities, e.g. ears and feet, are warm to the touch.
  • Anorexia.
  • Increase in breathing rate, with open-mouth breathing.
  • In some cases, blood-tinged fluid from the nose and mouth.
  • Dullness.
  • Restlessness.
  • Inco-ordination.
  • If the rabbit isn’t circulating enough oxygen then their mouth and nose with by cyanotic, i.e. blue-tinged.
  • If allowed to progress, the rabbit may collapse, have seizures, and die.

Hyperthermia is an emergency and treatment must be given rapidly. Call your vet and take your rabbit to your local veterinary clinic straight away for emergency treatment.

In the meantime, these simple steps can help reduce your rabbit’s body temperature:

  • Take your rabbit out of the warm environment and place it in a cooler, well-ventilated area.
  • Reduce body temperature slowly; if this is done too quickly it can cause stress sending your rabbit into shock which can be fatal.
  • Wet the ears and blow them with a hair drier or convection fan on a cold setting.
  • Spray the body with cool water, in particular the belly area and between the back legs.

If the rabbit becomes more distressed, stop active cooling.

Check the temperature of your rabbit’s environment, it should be between 16-21°C.

Ensure your rabbit has accommodation which shelter it from excess temperatures, either heat or cold, and that it can move freely from a warmer area to a cooler area (and vice versa). In hot weather, fans or water sprays can help cool the environment. Bear in mind that the sun moves around during the course of the day, so ensure that if left alone, the rabbit will have shade throughout the day.

Obese or heavy-coated rabbits can have their hair clipped to reduce the risk of hyperthermia. Avoid stressing your rabbit by chasing it, especially in warm weather.