I used to occasionally host tours of my farm as a Chore Efficient model for other local farm owners to come out and take some of my best practice to consider taking away and doing themselves. About a year ago I was explaining my flooring in the stall and that only used one or two scoops a day and that a bag of pellets usually lasts me about a week.
One woman looking in my stall asked me what kind of pellets I used her wood pellets were WOOD PELLETS and mine look different than hers. I showed her my bag of Eagle Valley pellets and she asked why they looked to different in the bag than on the floor. Finally I asked her if she was soaked and dried them before she laid spread them in the stalls.
Not only her but almost half of the people on the tour didn't know that you are supposed to wet pellets, let them fluff up before putting in the stall. I am dead serious. I was completely flummoxed!
Now it makes me giggle thinking that some people out there are dumping hard wood pellets as "bedding". It's like the world’s worst bean bag!
But seriously though, if you have rubber mats you don't need a whole lot of bedding. In fact deep bedding actually encourages horses to urinate in their stalls. Horses don't like to pee where it will splash, the urea burns their legs so they prefer to pee where it doesn't splash, such as say, a deeply bedded stall.
If you have rubber mats, bedding should really only be used as a sweeping compound. You should only put enough down to allow for manure to easily be picked up and absorbed without leaving a damp spot on the mat.
When my mare foal in March I hated it but I did use straw, but my vet and farrier both recommended that once the foal was dry to go back to fluffed pellets and just make one corner deeply bedded for the foal to sleep in, which I still do as he’s almost 2 1/2 months old.
I don't think I have ever used 10 bags of bedding or pellets in a stall. Even after I cleaned the straw out (it made lovely mulch in my garden in March, and kept my veggies warm against the frost), I still only used two bags of fluffed up pellets, and even then the baby was madly cuddled up in fluff.
Unless you have a SEVERALLY arthritic senior horse, rubber mats are more than comfortable for horses, and anything more than bedding as a sweeping compound on top of mats or even better dirt, is an absolute waste of money. Horses don't perceive comfort as we do, and by trying to anthropomorphize them to our standard of comfort is naive and in the end a huge financial waste, your horses is literally crapping on wasted money, and in the end even worse for the environment. Overuse of bedding takes forever to decompose. Horse manure is actually nearly the PERFECT ratio of green and brown materials (carbon and nitrogen) for composting. Adding bedding makes the composting take significantly longer for everything to break down. Pellets are vastly superior to shavings because the amount of product required is exponentially smaller than traditional shavings, but even shavings are better than straw which, takes FOREVER to decompose.
That being said if you have concrete floor and no mats, then YES by all means, deep bed to your heart’s content because, yes the concrete by its self is horrible and you do need to provide a cushion for a sheet of rock.
As far as costs, I buy a 1 ton of wood stove pellets from a guy off Craigslist for about $160 and he delivers and stacks them for me and 1 tone lasts me a little over a year for one moderately messy, but giant horse.
Yes I use stove pellet; stove pellets are TYPICALLY the exact same product as horse pellet bedding, but without the "horsie" markup. Just make sure that the label indicates that they are additive and resin free.
Hope this helps!