Fever in horses: values and what to do

Normal values: what is normal?

The rectal temperature of a healthy adult horse is between 37.5 and 38.5 °C. Foals may run slightly higher, up to around 38.9 °C. Temperature can also rise slightly due to exercise, heat, or stress — so always measure at rest, preferably early in the morning as a reference value. Fever officially starts at 38.6 °C, but many vets use 38.9 °C as a practical lower threshold for concern. Record measurements in your horse's EquiSight profile so you can spot trends over time and don't have to rely on memory.

How to measure temperature correctly

Use a digital rectal thermometer with a cord or clip so it cannot be lost. Lubricate the tip with petroleum jelly or gel, stand to the side of the horse, and hold the tail gently to one side. After about 60 seconds the thermometer will beep. Clean and disinfect after each use.

• Always use a digital thermometer — analogue ones are too slow and too inaccurate
• Measure rectally, not under the armpit: that gives a reading that is too low
• Wait at least 30 minutes after exercise before measuring
• Record the date, time, and value — even when it is normal
• Keep a spare thermometer in your first-aid kit at the stable

Fever levels and corresponding action

Not every elevated reading calls for the same response. The classification below helps you decide quickly what to do.

• 37.5 – 38.5 °C: normal — no action needed
• 38.6 – 38.9 °C: slight elevation — monitor twice daily, record in EquiSight
• 39.0 – 39.5 °C: moderate fever — call your vet for advice, rest the horse from training
• 39.6 – 40.5 °C: high fever — vet same day, ensure shade and water
• Above 40.5 °C: emergency — call immediately, cool carefully with lukewarm water

Common causes of fever

Fever is always a symptom, never a diagnosis in itself. The most common causes in horses are viral respiratory infections such as rhinopneumonitis or influenza, bacterial infections, abscesses (including in the hoof), colic with an inflammatory component, and heat stress in summer. Young horses and older horses are more susceptible. Has your horse recently had contact with new stablemates or undergone transport? That considerably increases the risk of a viral infection. Always record contacts and travel in the EquiSight horse profile so your vet has a complete picture.

What you can do before the vet arrives

• Stable the horse or move it to shade, away from stable activity
• Ensure access to plenty of fresh drinking water — fever significantly increases fluid requirements
• Keep movement to a minimum: no training, no transport
• Measure every 4 hours and record the values, also for the vet
• Do not give fever-reducing medication without consulting your vet — it can mask the course of illness
• Use EquiCoach for a quick checklist when fever is suspected

Monitoring recovery and preventing relapse

Once the temperature has been normal for 48 hours, you can cautiously start bringing the horse back into work — but do not rush it. A common mistake is returning to full work too soon, causing a second fever spike. Schedule recovery weeks in the EquiSight calendar and use the notes section in the horse profile for vet notes and medication schedules. This keeps you organised and allows you to immediately share a complete medical history if another episode occurs.