Your horse seems lethargic, isn't eating properly, and is sweating—could it have a fever? Elevated body temperature is not a disease in itself, but rather a symptom and an important warning sign from the body. The challenge is to find the underlying cause. This is not always easy, as many different illnesses can cause fever. Horses with fever may have contracted an infectious disease. It is therefore particularly important to find the cause and isolate the horse as much as possible until then in order to reduce the risk of infection for other horses. 

In this guide, you will learn how to take your pet's temperature correctly, what temperature is normal, which accompanying symptoms provide important clues, and how your veterinarian systematically searches for the cause.

What is fever and why does a horse get a fever?

Fever is an increase in body temperature above the normal range. It is a natural defense reaction of the body against pathogens or other disorders. The elevated temperature supports the immune system in fighting infections.

Normal body temperature in horses:

• Adult horses: 37.5° to 38.2°Celsius 
• Foals: 37.5° to 38.9° Celsius (slightly higher than in adult horses) 
• Slightly elevated levels may also occur after exertion, during excitement, or on hot days.

When can we say that someone has a fever?

• Slightly elevated temperature: 38.3° to 38.9° Celsius 
• Fever: 39.0° Celsius or higher 
• High fever: above 40.0° Celsius – Immediate veterinary attention is required.

Have you measured your horse's temperature and are unsure of the cause? The specialists at Altano clinics can help you with a quick diagnosis. Find a clinic near you now. 

Taking a horse's temperature: How to do it correctly

The only reliable way to determine whether your horse has a fever is to take its temperature with a thermometer inserted into the rectum.

Step-by-step instructions for taking a temperature:

1. Use a digital thermometer—they are fast, accurate, and easy to read.
2. Disinfect the tip of the thermometer and apply some lubricant or petroleum jelly.
3. Stand to the side of the horse, not directly behind it. Safety first!
4. Carefully lift the tail and insert the thermometer about 5 to 8 cm deep into the anus.
5. Hold the thermometer at an angle against the intestinal wall, not in the middle of the intestine—this will give you the most accurate measurement.
6. Wait until the thermometer beeps (usually after 30 to 60 seconds).
7. Carefully remove the thermometer, read the value, and note it down along with the date and time.
8. Clean and disinfect the thermometer after each use.
9. Repeat the measurement if the value seems unrealistically high or low. Make sure that the horse is not defecating or that the thermometer is not stuck in a horse apple instead of touching the intestinal wall—this will result in falsely low temperature readings. 

Tip: It is best to always take your temperature at the same time of day, as body temperature can fluctuate slightly throughout the day. It is usually slightly lower in the morning than in the evening.

The most common causes of fever in horses

• Respiratory tract infections
  • Viral infections (e.g., equine influenza, equine herpes virus)
  • Bacterial respiratory tract infections
  • Bronchopneumonia (pneumonia)
• gastrointestinal disorders
  • Salmonellosis (very common cause of diarrhea and fever)
  • Inflammation of the intestinal wall (colitis)
  • Peritonitis (inflammation of the peritoneum – very rare, serious condition)
• parasites
  • Severe infestation with strongyles (e.g., larval cyathostomiasis)
• Skin infections or wounds
  • Abscesses or infected wounds
  • Phlegmon (abscess)
• Infectious joint inflammation
• Dental problems with abscess formation (root abscess, maxillary sinusitis)
• Reactions to medications
  • Vaccination reaction (slight increase in temperature often normal)
  • Drug intolerances (less common)

The specialists at Altano clinics will help you get a quick diagnosis. Find a clinic near you now.

Interpreting accompanying symptoms correctly: What else is noticeable?

Fever rarely occurs in isolation. The accompanying symptoms provide important clues about the underlying disease:

General condition: fatigue, apathy, head bowed, abdominal wall tense – symptoms indicating the severity of the illness

Respiratory symptoms: cough, nasal discharge (clear, purulent, or bloody), difficulty breathing, or increased respiratory rate 

Digestive symptoms: loss of appetite, colic symptoms, diarrhea, or changes in stool consistency 

Musculoskeletal system: Lameness, swelling of the legs, stiff gait

Mucous membranes: Discoloration of the oral mucosa (reddened, pale, yellowish) indicates circulatory or organ problems.

When is fever in horses an emergency?

Immediate action required in the event of:

• Fever above 104.4°F
• Fever combined with severe colic symptoms 
• Very poor general condition, the horse is apathetic or lying down and does not want to get up. 
• Shortness of breath or very rapid, labored breathing 
• Blue or severely reddened mucous membranes 
• Severely swollen limbs with warmth and pain, severe lameness (visible when walking)
• Foals with fever: Foals have an immature immune system and can quickly become critically ill, so any fever in foals should be taken seriously. Quick action is particularly important in the first few weeks of life.
• Pregnant mares: Fever during pregnancy can lead to miscarriage, especially in cases of herpes infection. Pregnant mares with fever should be examined immediately.
• Older horses: In older horses, fever can indicate more serious underlying diseases. The immune system often no longer works optimally, so special attention is required.

Veterinary check within the next 1-2 days for:

• Elevated temperature or fever below 104.0°F (40.0°C) that lasts longer than 24 hours 
• Fever with cough and nasal discharge or significant loss of appetite
• Recurrent fever without apparent cause

Is your horse or foal showing signs of fever? Altano clinics have experience with all age groups. Find a clinic near you now. 

The veterinary examination: detective work

 1. General clinical examination

A general clinical examination always begins with an assessment of the horse's general behavior: posture, facial expressions, breathing, feed intake, and responsiveness provide initial indications of the horse's state of health. This is followed by a systematic inspection and palpation of the entire body – starting with the head, neck, chest, back, abdomen, and limbs. The mucous membranes are assessed, the lymph nodes are palpated, and the skin is checked for swelling or injuries. This is followed by the vital signs, in particular temperature, pulse, and respiration. Measuring rectal body temperature is a key component, as is listening to the heart, lungs, and bowel sounds. Finally, circulatory status is assessed based on capillary refill time, skin turgor, and hydration.

This examination is the most important first step when treating a horse with fever. Only a complete general examination can reveal which organ system may be affected and whether there are signs of infection, colic, respiratory problems, or local inflammation. It is also essential for assessing the severity of the condition, identifying complications at an early stage, and deciding which further diagnostic measures—such as blood tests, ultrasound, or endoscopy—are appropriate and safe. A thorough general examination therefore forms the basis for any targeted diagnosis and treatment. 

 2. Laboratory diagnostics

• Hematology: shows signs of inflammation (elevated white blood cell count) 
• Blood chemistry: Checking liver, kidney, and muscle values
• Swab samples: For nasal discharge or wounds to determine the pathogen

 3. Imaging techniques and specific examinations

Imaging techniques such as X-rays, ultrasound, or endoscopy may be used depending on the symptoms to confirm or rule out suspected diagnoses. Depending on the symptoms, other diagnostic options may be used, including specific tests for individual infectious diseases or blood parasites.

Does your horse require comprehensive diagnostics? Altano clinics have state-of-the-art examination facilities and laboratories. Contact us now.

Treatment: What to do in case of fever?

Treatment always depends on the underlying cause. However, there are some general measures that can be taken:

Symptomatic treatment:

Fever-reducing medication—but only as directed by a veterinarian! Caution: Fever should not be suppressed before the cause has been determined, as it is an important warning sign.

Supporting measures:

• Isolate the affected horse to minimize the risk of infecting other horses. Closely monitor neighboring horses and also take their temperature.
• Rest and care – the horse should not be put under strain 
• Fresh water always within reach – fever leads to increased fluid requirements 
• Offer tasty feed – if your horse has no appetite, soak hay cobs or mash; as a general rule, offer sufficient roughage and reduce the amount of concentrated feed. 
• Temperature control – measure the temperature 2 to 3 times a day and document the progression.

Causal treatment depending on the cause:

Once you and your veterinarian have found the cause of the fever, your veterinarian will begin the necessary treatment. This can range from general support of the immune system to the administration of certain medications and should only be done in consultation with your veterinarian. In some cases, the fever subsides before the cause can be determined. In such cases, symptomatic treatment is usually given and the cause often remains unknown.

When can the horse be put under strain again?

• During the fever phase: Complete rest in the stall – no exertion! Even light exercise can worsen the condition. Only short walks for grazing may be possible if the veterinarian agrees.
• After the fever has subsided: Complete rest for at least 3 to 5 days after the last fever spike, then slowly build up training over several weeks.
• Important: Discuss the training plan with your veterinarian! Some illnesses require a longer recovery period than others.

Prevention: How to strengthen your immune system

Even though not every infection can be prevented, you can support your horse's immune system:

Keep vaccinations up to date: All horses in the herd should be vaccinated. The StiKo Vet (Standing Vaccination Commission for Veterinary Medicine) recommends vaccination against tetanus, influenza, equine herpes virus, and, in large parts of Germany, vaccination against West Nile virus.

Optimal housing conditions: Good barn hygiene reduces the risk of infection. Sufficient fresh air is important, and drafts should be avoided. Stress weakens the immune system.

Feeding according to needs: Sufficient roughage is essential for healthy intestinal flora. If necessary, vitamins and minerals should be supplemented. Vitamin D and zinc can support the immune system, especially in winter.

Regular exercise: Moderate training strengthens the immune system. Avoid both overexertion and under-exertion.

Would you like a personalized vaccination and prevention plan for your horse? The veterinarians at the Altano Group will be happy to advise you. Make an appointment.

Conclusion: Fever is an important warning sign.

Fever in horses is not a disease in itself, but rather an important symptom that can indicate various illnesses. Here is a summary of the most important points:

Measure your horse's temperature with a clinical thermometer – this is the only way to obtain reliable readings. Pay attention to accompanying symptoms – they provide important clues as to the cause. Take immediate action in the event of a high fever, poor general health, or critical accompanying symptoms. Have the cause clarified by a veterinarian – this is the only way to ensure targeted treatment. Allow your horse sufficient rest to recover.

With proper observation and quick action when needed, you can help your horse recover quickly.

For better readability, we predominantly use the generic masculine in our texts. It goes without saying that all personal designations refer equally to all genders. The abbreviated form of language is used solely to improve comprehensibility and is to be understood in an unbiased manner.