How to tell if my dog has a fever: complete guide

When your dog is not feeling well, the body tells you before any obvious symptom appears. Fever in dogs is one of those warning signals that you need to know how to identify, because acting in time can be important.

The problem is that, unlike humans, dogs cannot tell you they feel ill, and many of the symptoms of canine fever are easy to confuse with simple tiredness or a quiet day. In this article you will find everything you need to know to detect fever in your dog, understand what causes it and know when it is urgent to go to the vet.

What is fever in dogs?

Fever in dogs is a rise in body temperature above normal values as a response of the immune system to an infection, inflammation or other pathological stimulus. In practical terms, we talk about fever when the rectal temperature exceeds 39.5 ºC, although the normal range in dogs is between 38 ºC and 39 ºC. Contrary to what many believe, fever itself is not the problem: it is a defensive response of the organism, a sign that the body is fighting something. The problem arises when that temperature shoots up or is maintained for too long, because it can then cause damage to vital organs.

When can fever be dangerous?

A moderate fever — between 39.5 ºC and 40.5 ºC — is uncomfortable for the dog but does not represent an immediate danger if detected and treated in time. The critical threshold is 41 ºC: above that temperature, the risk of organ damage becomes real and the situation requires urgent veterinary attention. Very high fevers can cause severe dehydration, cardiac problems, neurological damage and even multiple organ failure if not controlled. Therefore, in the face of any temperature above 40.5 ºC, do not wait to see if it comes down on its own: call your vet or go directly to an emergency clinic.

Difference between fever and hyperthermia

Although both raise body temperature, fever and hyperthermia are not the same thing and require different responses. Fever has an internal origin — the immune system regulates it as part of its response — whereas hyperthermia is a rise in temperature caused by external factors, such as excessive heat, intense exercise or confinement in a closed space. Hyperthermia is not part of the immune response: the body does not ‘want’ the temperature to rise, it simply cannot regulate it. In practice, hyperthermia can be just as dangerous — or more dangerous — than fever, and heatstroke in dogs is a real veterinary emergency that should not be minimised.

What is the normal temperature in a dog?

The normal temperature range in a healthy adult dog is between 38 ºC and 39 ºC measured rectally. In puppies, this range may be slightly higher. It is important to bear in mind that temperature can vary depending on the time of day — it tends to be higher in the afternoon —, the recent level of activity or the emotional state of the animal. A dog that has just played intensely or is very stressed may have a slightly higher temperature without that implying fever. The reference of normal temperature is useful as a starting point, but it should always be assessed in the general context of the animal: a dog at 38.8 ºC but with other symptoms deserves as much attention as one at 39.4 ºC.

Common causes of fever in dogs

Fever is a symptom, not a disease in itself, and its causes can be very varied. The most frequent include bacterial, viral or fungal infections — such as distemper, parvovirus or leptospirosis —, as well as internal inflammatory processes, reactions to recent vaccines, poisoning and autoimmune diseases. In some cases, fever appears after a wound or bite that has led to a local infectious process. It can also be the first visible symptom of more complex systemic diseases that the vet will need to investigate through tests. One of the keys to identifying the cause is to note what other symptoms accompany the fever: vomiting, diarrhoea, coughing, limping or changes in behaviour are valuable clues to communicate to the vet.

• Bacterial, viral or fungal infections (distemper, parvovirus, leptospirosis)
• Internal inflammatory processes of various origins
• Reaction to recent vaccines
• Poisoning by toxic substances or foods
• Autoimmune diseases
• Wounds or bites with localised infection
• Systemic diseases requiring veterinary diagnosis

Symptoms of fever in dogs

The problem with canine fever is that its symptoms are easy to miss, especially in the first hours. The most common signs are apathy and lack of energy: a normally active dog that suddenly does not want to get up may be starting to develop a fever. Loss of appetite, trembling, a dry and warm nose — although this last indicator is much less reliable than popular belief suggests — and red or watery eyes are also frequent. In some dogs, fever also manifests as excessive panting without having exercised, or as seeking out cold surfaces. If your dog shows several of these symptoms at the same time, take its temperature: it is the only way to confirm it.

• Apathy and lack of energy for no apparent reason
• Loss of appetite or refusal to eat
• Trembling without cold or obvious stress
• Red or watery eyes
• Excessive panting without having exercised
• Seeking out cold surfaces to lie on
• Dry and warm nose (unreliable indicator on its own)

How to measure your dog’s temperature: steps

Measuring a dog’s temperature at home is perfectly possible, although it requires a minimum of preparation and patience. The most reliable method is the digital rectal thermometer: ear or forehead thermometers designed for humans are not accurate in dogs. Before starting, have the thermometer, petroleum jelly or lubricant ready, and if possible, a second person to help keep the dog calm.

1. Lubricate the tip of the thermometer with petroleum jelly or lubricating gel
2. Position the dog standing or lying on its side, with the tail raised
3. Gently insert the thermometer into the rectum, about 2-3 cm
4. Hold the position until the thermometer emits the confirmation beep
5. Remove carefully, read the temperature and note it down along with the time
6. Disinfect the thermometer before putting it away

If the temperature exceeds 39.5 ºC, call your vet. If it exceeds 41 ºC, go directly to an emergency clinic without waiting.

Fever in dogs is not always easy to detect, but knowing the symptoms, knowing how to measure the temperature and having a clear idea of when to call the vet makes all the difference. Most cases resolve well when you act in time and with clear-headedness, without panicking but without waiting too long either.

A strong immune system starts with quality nutrition. At OnlyFresh you will find dog food recipes made with fresh meats, natural ingredients and probiotics that take care of your dog’s health from the inside, without flours or dehydrated ingredients, so that it has the resources it needs to stay healthy.