Wow thanks for the fast and helpful responses!
So I expected that horses wouldn't lie down as much as cows, but I must say one hour a day is a bit of a surprise.
I deal primarily with EVA mats, which are a little more expensive than rubber mats but come with their own advantages. I imagine the rubber probably gets pretty hard and spread out over time, though I'm not sure that's even much of an issue considering the small time that horses spend lying down.
Reno Bay- don't the barn owners bolt the rubber mats down to the concrete to prevent bedding from getting under the mats? That's what we do in cow stalls and it's never been a problem. But again, obviously, I don't know if that is even an option in a horse stall.
Nice to know the information about washing, too. I must admit, though my embarrassment begs me not to, I didn't realize that horses sweated! Is it as much as us? How high is their tolerance to hot weather?
Rubber mats should also be used with bedding.