Here’s the thing about summer training: it’s not just about “it’s hot, ride less.” There’s actual science to this, and knowing the numbers means you can make better decisions for your horse - not just guess.
The 150 Rule (This Is the One to Remember)
Add the air temperature (in Fahrenheit) to the relative humidity percentage. That’s your heat index for horses.
- Under 130: Your horse can cool itself effectively
- 130-150: Cooling efficiency is decreased - work lighter, take more breaks
- Over 150: Your horse’s ability to cool itself is greatly reduced - keep work minimal
- Over 180: Dangerous territory - skip the ride entirely
Why does this matter? Because 85°F with 30% humidity (total: 115) feels very different to your horse than 85°F with 70% humidity (total: 155). The second scenario? That’s when horses start getting into trouble.
Why Humidity Is the Real Problem
Your horse cools itself primarily through sweat evaporation. When the air is humid, that sweat doesn’t evaporate - it just sits on the skin doing nothing useful. Your horse can sweat 2-4 gallons per hour during hard work, but if none of that is evaporating, body temperature keeps climbing.
This is why a horse in Arizona at 100°F with 10% humidity might handle it better than a horse in Florida at 90°F with 80% humidity.
Signs Your Horse Is Overheating
1. Elevated body temperature - Normal is 99-101°F. Over 103°F means trouble. Above 106°F = heat stroke.
2. Profuse sweating OR no sweating - If your horse suddenly stops sweating, that’s worse - the cooling system has shut down.
3. Elevated heart rate - Normal resting is 32-44 bpm. If it stays elevated after stopping, your horse is struggling.
4. Labored breathing - Normal is 8-16 breaths/min. Heavy, rapid, or shallow = trouble.
5. Lethargy or coordination issues - If your horse seems weak, wobbly, or “off,” stop immediately.
6. Dark urine - Sign of dehydration. Body is conserving water.
How to Train Smart in Summer
Adjust Your Schedule: Ride early morning or late evening. Yes, this might mean 6 AM alarms.
Keep Work Appropriate: Don’t ask for the same intensity. More walk breaks. Shorter sessions.
Water: Myth busted - you don’t need to withhold water from a hot horse. Let them drink.
Electrolytes: A sweating horse loses sodium, potassium, and chloride. If you add electrolytes to water, also offer plain water separately.
Airflow: Fans in the barn. Misting fans even better. Work in shade when possible.
How to Cool an Overheated Horse
If rectal temp is above 103°F, start cooling immediately:
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Cold water, continuously. Spray head, neck, back, rump, legs. Don’t stop.
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Scrape and repeat - or continuous hosing works too.
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Ice water is safe. Research shows it’s effective for very hot horses (above 105°F) - reduces core temp faster without causing muscle cramping.
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Call your vet if temp doesn’t come down or horse shows distress.
Who’s Most at Risk?
- Older horses - thermoregulation becomes less efficient with age
- Obese or out-of-shape horses - extra insulation, less fitness
- Horses with long coats (Cushing’s especially) - consider a body clip
- Young foals - more prone to dehydration
- Horses with anhidrosis - if your horse doesn’t sweat, summer is danger season
The Bottom Line
Summer training isn’t about pushing through the heat - it’s about being strategic. Know your numbers (temperature + humidity), watch your horse, and adjust accordingly.
The goal isn’t to stop training entirely. It’s to train smart, so you’re both still healthy come fall.
Want more practical training guidance? Check out my free lesson or explore the From Stiff to Supple course.
