Your bedding choice might depend on what is most readily available in your neck of the woods and your farm's capacity for storage. Bedding should be absorbent, soft, and free of dust, mold, or sharp objects.
Sawdust is adequate bedding. It's inexpensive, usually delivered by the truckload. It requires a dry space and must be double handled, as opposed to bagged shavings that can usually be dropped into the stall from the loft. Sawdust is very absorbent, which prevents urine from seeping into an organic stall floor. However, its high absorbency might mean that by morning the horse is standing in a sopping wet mix of manure, urine, and sawdust. Also, the wheelbarrow load that you remove while mucking will be very heavy. Sawdust can be just that, dust, which should be measured against the cost savings.
Ammonia, a by-product of urine, is a noxious gas that can be harmful to a horse's eyes and respiratory system. Hydrated lime can be sprinkled over wet spots of an organic stall surface. The lime will absorb excess moisture and alleviate acidity and the smell of ammonia.
You can obtain other sawmill waste products by the truckload, but they can be rough textured and you must make sure that the chips or shavings are from softwoods. Avoid hardwoods because they are not very absorbent, and some, particularly black walnut, can cause founder when in contact with a horse's feet, and death if ingested.
Straw is a very clean, non-dusty bedding option. It is ideal for a horse with a wound that must be kept clean or for use on a breeding farm. Shavings and most other bedding will adhere to a newborn, possibly interfering with his mucus membranes and respiratory system. Horses might tend to eat oat straw, so wheat straw is a better choice. However, some horses will eat either, and they should not have their stalls bedded with straw.
Straw comes in bales, like hay, and tends to be about the same price. Like hay, it must be properly stored and can be heavy and cumbersome to handle.
Pine Shavings, Kiln Dried and Bagged
Depending on what area of the country you live in, this material might be the most expensive type of bedding. It tends to be convenient, requiring the least amount of handling and is easily transportable. It is generally considered to be the most aesthetic, and if kept replenished, the most pleasantly smelling. It is easy to muck and can aid in the breakdown of a manure compost pile. It is soft, absorbent, and comfortable, which makes it ideal bedding for most horses. Pine shavings shouldn't be used for horses with dry foot problems or for a foaling stall.
How to Muck a Stall
A stall must be cleaned of manure and urine for sanitary purposes. Mucking the stall is basically like cleaning out a giant cat litter box. First, remove visible manure piles and urine wet spots. The tines of a mucking fork are spaced so that manure balls of a full-grown horse will remain on the fork while most bedding material will fall through. Turn over the middle of the stall, picking out the rest of the manure and wet bedding. The perimeter of a stall should be banked. Bedding mixed with manure can be tossed against the wall. The manure should roll down the banked shavings against the wall, making it easier to separate and remove. The hay corner and under the feed tub should be swept clean so hay chaff and spilled grain won't be ingested with bedding.