Fever in Horses: Temperature Chart, Red Flags, and What To Do
- Horse Education Online
- Oct 24
- 11 min read
Updated: Oct 30
A raised temperature is one of the earliest and most useful clues that a horse is getting sick. The challenge for owners is knowing what number truly counts as a fever, how to take an accurate reading, and when that reading means “monitor” versus “call the vet.” This guide walks you through a clear first hour plan, red flags that change the timeline, and the most likely causes by season so you can act with confidence rather than guess.
We’ll start by defining normal versus fever in adults and foals, then show you a simple way to take and trend a rectal temperature you can trust. Along the way, you’ll pair that number with heart rate, breathing, and gum checks so the whole picture makes sense. If you need a refresher on technique and normal ranges, keep these handy: The Horse’s Vital Signs and Average Heart Rate for a Horse. By the end, you’ll know exactly when to keep logging, when to isolate, and when to pick up the phone.
Answer Box
A normal adult horse’s rectal temperature is 99–101 °F (37.2–38.3 °C). Fever is >101.5 °F (38.6 °C); any fever in foals warrants urgent veterinary advice. In the first hour:
Confirm temperature with a lubricated digital rectal thermometer and recheck in 15–30 minutes.
Log heart rate, respiratory rate, gum color/capillary refill, attitude, appetite, manure, and note the time.
Call your veterinarian if temp is >102.5 °F (39.2 °C) or your horse is depressed, off feed, has diarrhea, a persistent cough/nasal discharge, colic-type pain, or neurologic signs.
Offer clean water; don’t give medication unless your vet directs you. Isolate if you suspect a contagious cause. See normal ranges and technique in The Horse’s Vital Signs.
What counts as a fever (and how to take it correctly)
Before we worry about causes, we need a number we can trust. Here’s how to define fever in adults vs. foals and take a clean, accurate rectal temperature that you can confidently track over the next hour.
Normal vs. fever thresholds (adults vs. foals)
In adult horses, a normal rectal temperature is 99–101 °F (37.2–38.3 °C). We consider it a fever once the temperature is >101.5 °F (≥38.6 °C). A reading of ≥102.5 °F (≥39.2 °C) or a value that keeps climbing on repeat checks is a red flag that warrants same-day veterinary advice.Foals run slightly warmer at baseline, but treat ≥102.0 °F (≥38.9 °C) as urgent, especially if behavior changes (quieter, not nursing, breathing faster).
Tip: Trend beats a single snapshot. Two readings, 15–30 minutes apart, tell you more than one.
Taking a rectal temperature you can trust
Use a digital rectal thermometer with a fresh battery and a small dab of water-based lubricant. Stand beside the hip, facing backward (not directly behind). Lift the tail gently and insert the lubricated tip about an inch (2–3 cm). Hold the device in place until it beeps—usually 60–90 seconds. Note the number and the time, wipe the probe, then disinfect (an alcohol wipe works well). If the result seems off or borderline, repeat in 15–30 minutes in the same calm setting.
Small technique tweaks that improve accuracy
A calm horse and consistent location lower stress-related spikes.
Lubrication ensures good probe contact (dry insertion can read falsely low).
Keep a tail-tie clip or loop on the thermometer if you have one so it can’t be “lost.”
Pair the temperature with quick vital checks
While the thermometer is working, scan the whole horse: attitude, appetite, breathing pattern, nasal discharge, cough, and manure output. Once you have the temperature, add heart rate, respiratory rate, and capillary refill time (CRT) so your data tell a coherent story. If you need a refresher on normal ranges and how to count beats and breaths, see The Horse’s Vital Signs and Average Heart Rate for a Horse.
Why this matters
A mildly elevated temperature in a bright, eating horse with normal HR/RR is very different from the same temperature paired with tachycardia, labored breathing, or muddy gums. The combination guides triage.
Reading the situation — clear, real-world examples
Adult at 101.8 °F (38.8 °C), bright, eating, normal HR/RR.Likely a low-grade fever. Recheck in 30 minutes and start a simple log (time, temp, HR, RR, gum color, behavior).
Adult at 102.7 °F (39.3 °C), off feed, HR 56 bpm, RR 28/min.This is a call-today scenario. Keep water available, begin isolation if respiratory signs are present, and don’t give medication unless your veterinarian directs you.
Foal at 102.1 °F (38.9 °C), quieter than normal.Treat as urgent. Phone your veterinarian now and keep the foal warm and hydrated while you wait.
First-hour plan: owner-safe steps
The first 60 minutes are about calm, simple actions that protect the horse and give your vet usable data. Set up the space, start a quick log, and make a few smart choices about hydration and isolation while you watch the trend.
Set the scene and start the clock
Move to a quiet stall or open aisle, halter and lead, and remove hay and grain. Leave clean water available. Note the time of the first elevated reading and how your horse looks: bright or dull, eating or off feed, any cough, nasal discharge, diarrhea, or colic-type behaviors (pawing, flank-looking, repeated attempts to roll). If you need a quick refresher on early illness clues, see How to Tell if Your Horse Is Sick.
Measure, then re-measure (trend over snapshots)
Confirm the rectal temperature with a lubricated digital thermometer, then recheck in 15–30 minutes. Capture heart rate, respiratory rate, gum color, and capillary refill alongside each temperature so you can show your vet a clear trend rather than a single number.
A simple first-hour log you can copy
Aim for every 30–60 minutes during the first hour, then hourly if stable.
Hydration and cooling—what’s safe to do now
Offer fresh water and allow normal drinking. If it’s hot or the horse is sweaty from weather or exercise, you can hose or sponge with cool (not icy) water and scrape to remove warmed water; repeat in cycles. Avoid chilling foals or compromised adults—dry them off and stop if shivering begins.
Heat stress or dehydration suspected?
Do not force electrolytes into a horse that won’t drink, but you may offer salt/electrolytes in water or feed to a drinking, otherwise stable horse. To estimate needs and plan a safe mix, use our Salt & Electrolyte Calculator.
Basic isolation if contagious signs are possible
If there’s coughing, nasal discharge, or diarrhea, treat the horse as potentially contagious. House separately if you can, use dedicated buckets and a footbath at the entry, and handle this horse last to reduce barn spread. Keep a short list of any new arrivals or recent travel.
What not to do in hour one
Don’t give NSAIDs (e.g., phenylbutazone, flunixin) unless your veterinarian instructs you—these can mask signs your vet needs to interpret and complicate diagnosis. Don’t blanket a hot or sweaty horse, and don’t withhold water.
Red flags: when to call or trailer now
Some combinations of temperature and whole-horse signs change the plan from “monitor” to “move.” Use these clear triggers to decide when to phone your veterinarian immediately or hitch the trailer.
Temperature and trend triggers
≥102.5 °F (≥39.2 °C) in adults or any foal ≥102.0 °F (≥38.9 °C).
A climbing temperature on the 15–30 minute recheck, even if still near threshold.
Whole-horse signs that escalate urgency
Severe depression or the horse goes off feed.
Colic-type pain, repeated attempts to roll, or no manure for many hours.
Diarrhea, especially watery or foul-smelling, or labored breathing at rest.
Green/yellow nasal discharge, harsh cough, or multiple horses in the barn with similar signs.
Neurologic changes (ataxia, odd stance, drooping lip/ear, abnormal mentation).
Why these matter
High fever increases fluid needs and can tip a marginal horse into dehydration or lameness-like pain from muscle soreness. Neurologic or respiratory compromise changes transport and biosecurity decisions immediately.
Call vs. load—deciding fast
Call your veterinarian now if any red flag above is present or if you’re unsure. If your horse is deteriorating, your vet may advise you to trailer directly to the clinic. While you’re on the phone, keep logging vitals so you can report a trend (e.g., “102.7 → 103.1 °F in 30 minutes; HR 56 → 64 bpm”).
Be trailer-ready (2-minute checklist)
Fuel, hitch, lights, and mats checked; route confirmed.
Minimal bedding, easy-remove halter, and a water source.
One calm handler, no unnecessary barn traffic around the horse.
What not to do during emergencies
Don’t stack multiple drugs trying to force the fever down; it can obscure diagnosis and carry risks. Don’t delay the call while waiting for a “perfect” set of numbers—report what you have, including behavior and trends. And don’t mix horses or share equipment if a respiratory or diarrheal cause is possible; keep isolation in place until your vet advises otherwise.
Bottom line: A high or rising temperature, foal fever, and any combination of depression, colic pain, diarrhea, breathing difficulty, purulent discharge, neurologic signs, or a barn cluster move you from “monitor” to call or trailer now. Keep water available, keep logging, and follow your veterinarian’s instructions.
Likely causes by season & context (owner overview)
Fever is a sign, not a diagnosis—and the season and setting narrow the list fast. Match what you’re seeing in the barn to common patterns so you can isolate appropriately and brief your vet with the right suspicions.
Respiratory cluster in the barn → Strangles is on the list
If multiple horses are coughing, have swollen glands, or thick nasal discharge, treat it like strangles until proven otherwise. Move the febrile horse to a separate area, switch to dedicated buckets and tools, and handle that horse last. Your vet may swab for PCR and culture, and advise stall-side isolation protocols. Deep dive: Strangles in Horses: Symptoms, Isolation, Biosecurity, Vaccination.
Clues you’ll notice first
Purulent (green/yellow) discharge, persistent cough, firm or painful submandibular area, other horses “coming down with something.”
Fever can precede discharge by 24–48 hours—isolate on fever + cough alone.
Summer near waterways + fever with diarrhea → Think Potomac Horse Fever (PHF)
PHF risk rises mid- to late-summer, especially where aquatic insects are common. Horses often present with fever, depression, and diarrhea; laminitis risk is non-trivial. Call your vet promptly—early fluids and targeted antibiotics matter. Learn patterns and timelines in our case series and symptom guide:
Owner actions while you wait
Keep the horse drinking, continue vitals every 30–60 minutes, and do not give NSAIDs unless your vet directs you (they can mask severity).
Mosquito season + fever with neurologic signs → West Nile Virus is a concern
Ataxia, hind-end weakness, muscle tremors, or abnormal mentation alongside fever in late summer or fall raises concern for West Nile Virus (WNV). This is a call-today situation. More on signs, treatment, and prevention: West Nile Virus in Horses: Symptoms, Treatment, Vaccination, and Prevention.
Transport & handling
Keep the environment quiet and well-bedded. If trailering is advised, pad corners and drive gently; a neurologic horse may lose balance.
Dry, warm months + firm swellings on chest/belly/limb → consider Pigeon Fever
In late summer and fall, firm, painful swellings over the pectoral region, along the ventral midline, or on a limb that later soften and drain point to pigeon fever (Corynebacterium pseudotuberculosis). Flies and contaminated gear spread it.
Owner actions while you wait
Isolate immediately, start a vitals log every 30–60 minutes, and do not lance or squeeze at home. Keep the stall clean and fly-managed. Full guide: Pigeon Fever in Horses: Signs, Abscess Care & Isolation.
Prevention snapshot—keep vaccines current
Outbreak seasons are kinder to barns with up-to-date vaccination. Review what your 5-way covers and how to time boosters relative to local risk: 5-Way Equine Vaccine: What It Covers and Why It Matters.
Quick season-and-context matrix
What to tell your vet (so triage moves fast)
A tight, structured update saves precious time and leads to better advice on the first call. Use this script and checklist to share the trend, key vitals, and recent exposures without hunting for words.
The 20-second script (say it just like this)
“Adult gelding, 12 years. Temperature 102.7 °F 30 minutes ago, now 103.1 °F. Heart rate 56 → 64 bpm. Respiratory rate 20 → 24/min. Gums pink, CRT 2.5 seconds. Off feed, small cough, no diarrhea. New mare arrived 5 days ago from a show, stalled next door. No meds given. Vaccinated in spring.”
That single sentence answers what, how fast it’s changing, how sick he looks, exposures, and what you’ve already done.
Fill-in template you can copy
Signalment: Age, sex, use (e.g., 10-yo mare, trail).
Temperature (trend): “102.0 → 102.6 °F in 30 min.”
Heart/respiratory rates: “HR 44 → 52 bpm, RR 16 → 22/min.”
Gums/CRT: Color and refill time.
Behavior/appetite/manure: Bright vs dull, eating or not, last normal manure.
Key signs: Cough, nasal discharge, diarrhea, colic pain, neuro changes.
Exposure history: Recent travel, shows, new arrivals, barnmates sick.
Recent treatments: Vaccines, dewormer, antibiotics, NSAIDs (or none).
Context: Season, heat/humidity, heavy insects, proximity to waterways.
Ask: “Do you want NSAIDs, fluids, or isolation steps before you arrive?”
Keep your first-hour log handy so you can read numbers directly. If you need ranges or technique refreshers while you measure, see The Horse’s Vital Signs.
Examples that change the plan (so you know what matters)
Rising temp + tachycardia, off feed: likely same-day exam, no meds until vet advises.
Fever + diarrhea in August near a creek: flag PHF risk; mention laminitis history if any.
Fever + cough with two barnmates sick: treat as a respiratory outbreak; confirm you’ve isolated and have separate buckets.
Foal ≥102.0 °F, quieter than normal: urgent—say the word “foal” first in your call.
After the call—what to keep recording
Continue temperature, HR, RR, CRT, and behavior every 30–60 minutes until your vet says otherwise. Note any new signs (first watery diarrhea, new cough, nasal color change), intake (water drunk, feed refused), and output (manure/urine). This timeline is often what leads to a faster, more accurate diagnosis.
FAQ
What thermometer should I use and how often should I recheck?
A digital rectal thermometer is fastest and safest. Keep a spare battery and a dab of water-based lube with it. Insert about an inch, wait for the beep (usually 60–90 seconds), and record the time with the number. If the reading is borderline or unexpected, repeat in 15–30 minutes in the same calm setting—trend beats a single snapshot. Pair each reading with heart rate, respiratory rate, and gum color/CRT so you and your vet see the full picture. Need a refresher on technique and normal ranges? See The Horse’s Vital Signs and Average Heart Rate for a Horse.
Is a temperature of 102 °F an emergency?
Context matters.
Adult at 102.0 °F (38.9 °C), bright and eating: recheck in 15–30 minutes and start a vitals log. Call if the number climbs or other signs appear.
Adult ≥102.5 °F (≥39.2 °C) or a rising trend: call your veterinarian today.
Any foal ≥102.0 °F (≥38.9 °C) or a foal that’s dull or nursing poorly: urgent veterinary advice now.
Can I hose or cool a febrile horse?
Yes—if heat stress or hot weather might be contributing, you can hose or sponge with cool (not icy) water, then scrape to remove warmed water; repeat in cycles. Keep the horse out of drafts and stop if shivering starts. With foals or compromised adults, be gentler: focus on shade, airflow, and hydration, and follow your vet’s guidance. Remember, cooling doesn’t treat the cause; it buys comfort while you monitor the trend.
When should I isolate a horse with fever?
Err on the safe side if you see coughing, nasal discharge, or diarrhea, or if several barnmates are coughing. House separately, use dedicated buckets/tools, handle the febrile horse last, and start a simple stall-side log of temps and signs. Your vet may recommend testing (e.g., PCR for strangles) and specific biosecurity steps. For an overview of respiratory outbreaks and isolation basics, review our Strangles guide.
What if the fever resolves after an hour—are we done?
Not quite. A “down then up again” pattern can hide under NSAIDs or natural fluctuation. Keep logging temperature, HR, RR, CRT, appetite, manure, and behavior for at least 24 hours after the last elevated reading. Call your vet if the fever returns, other red flags appear (off feed, diarrhea, labored breathing, neurologic signs), or if you’re in mosquito season or mid-summer near waterways where West Nile Virus or Potomac Horse Fever risks are higher. For prevention context and vaccine timing, see the 5-Way vaccine explainer.
Comments