Last winter I bedded the run-in for my boy's paddock. It had a railroad tie across the front, which held the shavings in. I used pine shavings. I noticed that they definitely lay down in there more when there was a bed of shavings. When we'd have periodic melt-offs, and I would replace the wet shavings with dry, they'd actually stand around and wait for me to be done so they could get in there and roll in the shavings. I felt it raised their comfort level to a significant degree.
This winter they're in a pasture with about 5 other horses, and they all share a run-in that is not bedded...it's larger than the old one, and I can't take it on to bed that thing for all of them - plus, my boys are not at the top of the pecking order, so if I did, it's likely they wouldn't get too much good out of it.
The three resident equines here share a partitioned 10'x24' runin as their only shelter, tho there is another identical shelter at the bottom of their paddock which they never use.
Both sheds have rubber mats and Boreal pellets (Agway). The used shelter is closed off to them in daytime provided the weather is ok, and left accessible to them at night.
We have 2 geldings, both 28, and a mare, 12. All three use one of the stalls as their bathroom almost exclusively at night, so a fair amount of bedding is used in it.
I love the pellets because they are super absorbent, last a long time and compost much more easily than shavings. While I have always loved the fluffy quality of the shavings, the pellets have proven to be much easier to deal with and much more economical for our situation.
Form follows function, or does function follow form?
I have my horses out on large fields with run-ins. The floor is just dirt; I pick up any poop inside each day, if there is any (there only is if the weather is bad -- otherwise they don't use the run-ins). I suppose it depends on whether you think your horse is going to use the run in to lie down and how big an area you are talking about. In my opinion the horses do just fine lying down out in the field; however if you find your horse really likes to lie down in a bedded run-in and you want to spoil him, go ahead and bed!
Mine have one end of the steel hoop barn (hay and tractor storage) for their run in. The only use it for shade, near as I can tell. Its been there for a bit over a year and they have never peed or shat in it. Now that we've moved the water trough under the shelter and subdivided the field into several paddocks that may change. I never thought I could have horses without shoveling s*%t but so far, so good. No bedding since they only ever lie down in there for a roll after a ride. The soil here is very very light and sandy so no mud, thank the good Lord.
Mine was dirt floor, but I threw down PDZ (especially in summer) and pelleted shavings. I only really cleaned it out every few days...but the shavings absorbed urine and such as it seemed like they spent a lot of time in there.
A good horseman doesn't have to tell anyone...the horse already knows.
I have three horses. In my back pasture I have a two stall 10x24 run-in. In my front pasture I have an undivided 10x24 run-in. When they are in the back, the two big guys each take a stall and the little guy floats - he divides his time sharing with one or the other. Both run-ins have a gravel base with stone dust on top and then mats. Before the mats I would end up digging to China and having to replace the stone dust on a regular basis because they would always come in to pee. Now that they are matted, in the summer I put a very thin layer of shavings in there to capture the rare urine event - they don't like to pee on the mats because it splashes on them. In the summer they prefer to lay down outside. In the winter they spend more time in the run-in so I put down 5 bags of woody pet or pelletized bedding in each stall (10 in the undivided run-in). I then put three to four bags of shavings in each (8 in the undivided). When they urinate it goes straight down to the woody pet and is absorbed in one spot. Once the pellets have reached the saturation point they will form clumps and thats when you remove the urine.
This not only cuts my shavings use in 1/2, it also saves in labor. I can go much longer before I have to strip the stalls and they are very easy to clean.
When I had my run-in, I matted it first, then put down pelleted bedding. It dries out quickly should it get wet. And although I'm not a fan of pelleted bedding in barns, (Find it smells) the pelleted bedding receives enough ventilation in a run-in to keep it smelling fresh.
My two are on a combination of fine and coarse shavings, in a deep-litter system. They run into a 30 x 40 shed which is actually half of the barn. The deep-litter system is working out fabulously. In the past, I have also done this using a combination of peatmoss and topsoil, also very nice.
My run-in is actually an extended roof attached to the barn, and the horses hang out there A LOT. It's a 36 x 10 foot area, and this last spring I finally enclosed it along the ground with old RR ties, which helps keep it neater and drier. The footing is a mixture of sand and soil, and every couple of months I add about six bags of pelleted bedding, which fluffs things up really nicely and keeps the dust down. I pick out the poop almost every day in the winter, every day in good weather, and that keeps it from getting too messy. In the winter it's much wetter, so in addition to the major pellet additions I usually add 1/3 bag per week on the wetter spots. I don't soak the pellets--they just break down on their own.
Our four geldings are out 24/7 in the spring, summer and fall and use our 40" X 12" run-in for shelter. We just use bagged shavings on the floor, and pick it out daily. We also have our 5 stall barn for severe weather and winter.