Hot and humid summers can be tough on humans and even tougher on horses, horses rely on us to choose how they deal with the heat.
Horses can live outside 24/7 if provided with 2 very important things: Fresh water at all times, and shade, somewhere they can go to get out of the direct sunlight and heat. As for water it must be clean and drinkable, all horses in the paddock must have access to it, no matter the height of the horse or pony. If horses are stalled at night, it is advised that they have 2 water buckets as they will drink more in the heat. Buckets get slimy after a day or 2 so also dumping buckets out and scrubbing them is a must. Slim build up will result in bacteria ingested by the horse. Provide free choice mineral/salt licks in pastures unless they are in the horses stalls.
Shade can be in the form of large trees, and or run in shelters big enough for all horses in get out of the heat together, as they normally travel in packs. Providing UV ray scrim sheets/ light summer fly sheets will also protect horses from the bug bites and the elements, Fly masks are also a good idea so horses don't get bug bites around their faces and then their faces swell up most times.
Horses that have light faces and or light pink noses may need sunscreen as well applied everyday they are outside and or exposed to the sun. Chesnut horses with pink noses are very susceptible to burns on their noses. In the hot and humid summer months horses maybe be left inside during the day to avoid the UV rays and turned out at night to be more comfortable while being outside.
If possible and the weather is decent open all barn doors and windows to allow airflow through the barn to cut down on the heat being trapped inside. Installing fans on each horses stall front is advisable if possible to give each horse its own cooling system when stalled to avoid over heating. While being stalled horses need access to hay and fresh clean water at all times and electrolytes would be advisable too to encourage the horse to drink in the humid weather.
Be fair to your horse and avoid working him/her during the high temperatures, ride very early morning or later at night to avoid the humidity. If you must work your horse only ride for about 20-25 minutes at a time with more walk times in between other excersises. Effective warming up and cooling down are crucial in the summer times, hosing horses off after a workout will help bring down their body temperature and reduce heavy breathing. Don't let your horse stand still to cool down, keep him walking until his breathing returns to normal.
During the summer keep an eye on your horses drinking habits and make sure he is taking in lots of water to stay hydrated to avoid vet bills.