Where I board there is three cats. Two of them Stacy found on the side of the road... looked like they were dumped since there was kittens that had been ran over. So she brought them back and had them fixed. They tend to use the arena for the litter box so that isnt a problem. Also we don't feed them tons of food. Enough to keep them from starving but it gets them to hunt more... and it works. They have good bellies on them so don't think they are starving, also they either lay in the hay or on a blanket we have sitting out. The winter coats on them are really thick and the cold weather doesnt seem to bother them.
I'm not sure how many barn cats I have at the moment, 2 for sure sometimes more. I can't catch any of them, they just come to eat and sleep. I have a small opening in my barn, just big enough for a cat to get through. I've been feeding them for maybe 10 years, out of the 15-20 cats that have been out there, only 2-3 have been friendly enough to pet.
I don't keep a litter box and I never go looking for cats. They get dumped or they just show up feral and I feed them. I have no mice in my feed barn and if they leave my chickens alone they are welcome to stay.
I posted on Craigslist asking for already speutered cats for my BO. The mice were everywhere, and so tame they'd stop to say hi after you shook four of them out of the blankets sitting there for 5 minutes. You wouldn't BELIEVE how many ads I got for "declawed indoor cat who needs to go. He/she's never been outside, but it loves to chase toy mice so it's be a great hunter" I mean really!
In the end we got two great girlies who can go in/out of the heated tack room whenever they want (w/ dry food and a litterbox) They are great hunters and very sweet, but you can NEVER let Boz in to the bathroom, she doesn't understand that potty time is private time
The barn cats we have are the animal shelter rejects. We pick the ones that nobody wanted or were returned because they didn't do well indoors. A couple of them are anti social and hide in the rafters all day but most of them get real friendly after a while. We feed them out of a big tray that they share with the chickens and the dog. The dog is a border collie. He likes to work all the time. He thinks he's rounding up all the horses but they ignore him.