Many horses have to spend at least a part of their time indoors in a stall. There are several possible reasons for this. If your horse has an injury, 'stall rest' may be required. Some horses may need protection from cold or wet weather. Show horses are often kept indoors so their coats don't fade and to avoid injury—such as bites and kicks from pasture mates. It may be appropriate to bring some horses in order to feed them, so you can see how much they've eaten and ensure pasture bullies don't steal their meal.
If pasture is sparse, keeping a horse stalled ensures they don't graze the grass down until it's damaged. During the winter months, ice can turn pastures and paddocks into dangerous skating rinks. Alternatively, sometimes, it's simply a matter of 'that's how we do things'.
But there are many disadvantages to keeping your horse in a stall, especially over long periods of time. Horses need a lot of exercise, and a stall restricts this natural outlet for energy. While some might keep their horses stalled to prevent injury, stall accidents like getting cast (caught upside down on its back), becoming entangled in buckets, door latches and feeders or getting loose and gorging on stolen feed, do happen. Stabled horses may be more prone to impaction colic as inactivity leads to lessened digestive motility. Poor air quality in stables can lead to respiratory problems like COPD, and damp stalls can cause hoof problems like thrush.
But the physical disadvantages are not the only ones. Horses are very social animals, and keeping them separated may be very stressful. Boredom can lead to bad habits such as stall walking, cribbing, weaving, wood chewing and bad behavior while being handled. It's not unusual for horses who spend a lot of times indoors to kick and strike walls, or lash out at passers-by with flattened ears and bared teeth.
A horse that is kept stabled might be more difficult to train as the first portion of the lesson may be spent blowing off steam, rather than learning anything. Stress can also lead to EGUS and spasmodic colic.
Overall, it's better for horses to spend some time—or all the time, outdoors. So it's wise to take a good look at why you are keeping your horse indoors and find ways to minimize the stall-time. If you bring your horse indoors simply out of habit—and many people do, take a look at the condition of your fences and pastures and see if your horse wouldn't be safer and happier outdoors. Some horses are stressed by an any amount of stall time. Others may beat on the barn door to come in anytime a few drops of rain fall, or a cold wind whips up. Every horse is different, and some will have definite ideas about where they want to spend their time. Sometimes it may be best to keep horses in overnight or for part of the day. Some stables that have night turn-out during the summer so the show horse's coats aren't sun bleached, but reverse the turn-out times during the cold winter months.
If you must keep your horse indoors be sure that its stall is mucked out frequently. Wet bedding can damage hooves and the ammonia fumes from urine can affect the horse's lungs.
Add the dust of hay, and the dusts and molds that tend to float around in stables and you many have a recipe for COPD. A radio playing, goats, barn cats, frequent human visitors, or another horse stalled next-door can provide companionship for a stalled horse. Of course, your hay needs to be dust free and excellent quality if your horse isn't getting pasture grass. Hay fed in frequent, small amounts is better than having your horse fill up on one or two big meals and then stand bored for the rest of the day. Of course there should be fresh water available at all times. Check automatic waters and bucket for cleanliness often.
Ideally, your horse can live outdoors 24x7, but it's not always possible. Balance turn-out time with stall-time and keep your horse's indoor environment healthy. A healthy environment means a happy, healthy horse.