Providing a horse with shelter is covering just one of this animal's basic needs. You might think that because horses spend most of their time outside, they do not need shelter. After all, wild mustangs run free on the prairie and do not seem to mind, right?
Sadly, that is an assumption, and not a very good one. Even wild horses will look for shelter from storms because they know that storms can be dangerous. Many times, wild horses will look for trees under which to graze when the weather is too hot, or cave openings when the storms are bad.
In the freezing cold, you will find wild horses forming a large, tight circle. Their back-ends face outward to the cold and the predators and their faces, necks, and front legs face inwards. With that many horses grouped this way together, their combined body heat helps them stay warm, while their hind legs are ready to kick predators away. That said, here are several reasons why your domestic horse needs shelter.
Sleep
Horses sleep standing up. They sleep for less than three hours a day. Horses do sometimes lay down when sleeping. This is the time that horses reach REM sleep, the deepest level of sleep, and the most restorative. Domestic horses may lay down in the field, but they are much more comfortable laying down in a lean-to or a basic horse shelter where they feel safest to fall into REM sleep.
Foaling
Mares will separate themselves from the herd to give birth to their foals. In the wild, they will find a large patch of scrub brush to hide themselves in while in labor. This is not all that different with domestic mares, who will look for a quiet, comfortable place to foal. Shelters provide your mare(s) with what they need to foal (if applicable).
Sunburn
Horses get sunburn! As a general rule, there is not much you can do about this besides providing your horse with a shelter where it can retreat during the hottest hours of each summer day. It also helps if you can provide them with lots of cool water to drink, and/or an occasional cool bath to soothe their hot skin. Some horse owners pamper their four-legged riding buddies by providing a continuous sprinkler of cool water under which to walk, along with a generous shelter through which their animals can walk or enter when they want to get out of the heat.
Frostbite
Just as horses can get sunburn, they can also get frostbite. Most horses are just fine when the temperature outside is between twenty and forty degrees Fahrenheit. However, if your horse experiences below-zero temps for several hours, his/her ears, tail, nose, and a few other parts could be affected by frostbite. If your horse has shelter, he/she can huddle together with other horses in the shelter to prevent frostbite. If the winters where you live are especially and dangerously cold, then you should consider constructing a heated barn and adding trough heaters for the water to prevent freezing.
Predators
There are still areas where cougars/mountain lions, bears, wolves, and other large predators live and roam. These predators are not intimidated at all by the proximity of your home to your horses. If these predators are hungry, they will jump into the field with your horses and chase after them. Most horses will just run away, but sometimes they head for shelter in order to protect themselves. They will either face inward and kick outward at predators (like wild horses), or they will face outward, ready to rear up and kick predators who try to leap toward them.
To learn more about horse shelters, contact a company like Rarin' To Go Corrals.