Fever in dogs

Your dog is lying flat, not eating, and his ears feel hot? Normal temperature in a healthy dog is between 38.0 and 39.0°C. Above 39.5°C is fever, above 40.5°C it is high fever, above 41.0°C a genuine emergency. Here you will learn how to measure fever reliably, what causes it, and when you must go to the vet straight away.

Temperature chart: what do the values mean?

Not every elevated temperature is equally dangerous. The table below shows what each reading means:

Small breeds tend to have slightly higher resting values than large breeds. After intense exercise, temperature can temporarily rise to 39.5°C without indicating illness. Always measure after 30 minutes of rest.

How does fever develop?

Fever is a protective reaction of the immune system. Specific chemical messengers called pyrogens signal the brain to raise the body's set temperature. At higher temperatures, bacteria and viruses replicate less effectively while immune cells work more efficiently.

When temperature exceeds 40°C, the body's own proteins are denatured and organs are put under stress. Prolonged fever can lead to organ failure or circulatory collapse. Fever above 41°C is life-threatening.

Recognizing accompanying symptoms

The most reliable symptom is the measured temperature. Without a thermometer, you can spot fever by these signs:

Other typical accompanying symptoms:

• Apathy and listlessness, dog lies flat and barely moves
• Loss of appetite and refusal to eat
• Drinking more than usual or refusing water entirely
• Fast, shallow breathing without exertion
• Glassy or dull eyes
• Shivering despite normal room temperature
• Fever stool: very dry, hard stools due to reduced intestinal activity

Severe fever can cause seizures. That is an immediate emergency.

Step by step: measuring fever correctly

Only rectal measurement with a digital thermometer is reliable in dogs. Ear thermometers are too inaccurate due to hair in the ear canal.

What you need: digital thermometer, Vaseline or lubricant gel, quiet space.

1. Lay the dog on its side or have a second person hold it
2. Apply a small amount of Vaseline to the thermometer
3. Lift the tail gently
4. Insert thermometer about 2 cm into the rectum
5. Hold steady until the beep sounds (usually 30–60 seconds)
6. Remove carefully, read and note the value
7. Clean the thermometer and label it (use a separate thermometer for your dog)

Dogs unfamiliar with this process need some getting used to it. Start practising in puppyhood so it causes no problems in an emergency.

What you can do at home

For mild fever (below 40°C) with an otherwise stable dog, you can initially wait and take these steps:

Cool environment: Move the dog to a cool, shaded room. No direct sunlight, no heating nearby.

Cool paws and belly: Apply damp, cool (not ice-cold) cloths to paw pads, belly and inner thighs. This reduces temperature from the outside. Important: do not pour cold water directly over the body as this constricts blood vessels and prevents heat release.

Offer water: Place fresh water within reach. If the dog does not drink, you can carefully offer a little water with a spoon. Never force it.

Rest: Reduce walks to a minimum. No sport, no playing.

No human fever medication: Ibuprofen, paracetamol and aspirin are toxic to dogs. Even small amounts can be fatal.

Causes: why does my dog have a fever?

Fever is almost always a symptom of another underlying condition:

Infections from bacteria, viruses or fungi:

• Lyme disease, anaplasmosis, babesiosis (tick-borne)
• Distemper, leptospirosis, parvovirus
• Bronchitis, pneumonia, gastrointestinal infection
• Mediterranean diseases (leishmaniasis, ehrlichiosis)

Inflammation of internal organs:

• Intestinal, pancreatic or liver inflammation
• Joint infections, middle ear infections, anal gland infections

Other causes:

• Poisoning, bite wounds, penetrated foreign bodies
• Vaccine reactions (mild fever 24–48 hours after vaccination is normal)
• Tumours and cancer
• Heatstroke (see section below)

Heatstroke vs. fever: knowing the difference

Heatstroke and fever have very similar symptoms but are different emergencies with different causes.

Fever comes from within through illness. The immune system actively raises body temperature.

Heatstroke comes from outside: the body can no longer release the heat it has absorbed. Typical triggers are prolonged sun exposure, a hot car or intense exercise on a hot day.

First aid for heatstroke: move the dog to shade or a cool room immediately, cool paws and belly gently with lukewarm water, call the vet straight away. Heatstroke is a life-threatening emergency.

Fever in puppies and seniors

Puppies under 8 weeks have an incompletely developed immune system. Fever can develop very fast and unpredictably in them. Even at 39.5°C you should inform the vet if you have a young puppy.

Newborn puppies (under 4 weeks) have a normal temperature of only 35.5 to 37.0°C. Falling below that is also serious.

Seniors from about 8 years often have pre-existing organ damage and a lower tolerance for high fever. Do not wait with older dogs: go to the vet already at 39.5°C.

What the vet can do

The vet lowers fever with injections, suppositories or medication such as carprofen. The cause is then investigated. Because fever can have many causes, diagnosis is not always straightforward. Tell the vet about everything unusual in the last few days: behaviour, food, tick contact, outings.

For bacterial infections antibiotics are used. Body temperature returns fully to normal once the underlying disease has been treated.

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