We once had so many mice in our barn that as soon as I fed the horses their grain, a little parade of young mice would form and run along the stall wall, ready to jump in the grain buckets as soon as the horses' noses were out of them. (It was really cute! - but...) I once caught six in one night in a Tin Cat (live trap, which work great by the way!) We had to kick our inside cats out of the house - long story involving urine - but they aren't suffering, have heated beds, heated water, and a little elevated entry to the tack room that only they can fit through. I haven't seen a mouse or any sign of a mouse in the barn for over a year. These were house cats, mind you. Cats are amazing, and even feral cats that are re-homed as kittens can be friendly and wonderful barn companions as well as major mice killers. There are issues regarding songbirds etc, but if you have lots of mice, I think that keeps the cats pretty busy. Our cats even keep the rabbit population down some, surprisingly.