I bought both mares as young horses ( 2 and 3yrs old) from their breeders. Both grew up out 24X7 and were in a stall for vet visits but mostly outside living as far as I know. One is very neat and the other is a pig. I do not know the particulars but I gather they lived the same.
The neat mare is neat even in her pasture - she does not just poop everywhere, she poops on the outer edges of the pasture. Messy one goes where ever she feels like going. Messy one is more claustrophobic than the neat one. Messy one LOVES her stall in the summer. As soon as the sun comes up she is in the stall standing under the fan and she doesn’t leave until it gets dark and the bugs are not out. Her door is open 24/7 so this is her choice. Neat one is out at night in the summer and gets really pissy if I don’t bring her in when the bugs are out. In the winter the flies die down so the horses go out in the AM and again messy horse has her door open 24/7 unless it drops down into the 20’s. Messy one has a large pasture and will walk all the way across the pasture to poop in her stall. I give up on her!
I am in Alabama and we don’t get really cold weather here. I still have a few flies here during warmer days. I was still running the fly system in November. NOBODY likes to be out when the flies are out so I do turnout accordingly and I have to change things up when we have rain. I am working from home so I can accommodate the horse’s preferences.
I only have 3 horses and 3 stalls. The mares ( BFF’s) are next to each other, the pony across the aisle. Both mares are grown-ups now so no young horses. Messy one works a few hours a week or less, the rest of the time she is grazing or eating hay, in or out, as she prefers. Not much stress there! I only shut her stall door and lock her in on really cold nights which only occurs a few nights a year and when that happens the other horses are in with her and she can see her BFF over the wall.