We have all our stable cats from the Cats Protection League in the UK. They are without exception feral cats which have turned up at the charity for some reason or another. They are kept confined in one of the stables, in a large (great dane size) dog cage with lots of places to hide and the cage half covered so they have a dark place. This apparently makes them feel secure. We feed and water them twice a day in the cage (there's a litter tray in there too which is kept clean). The stable door is left open so that they can hear and see whats going on around them. After two weeks, in the evening when everyone has gone we open the door of the cage and leave their food just outside. Usually the next day they will still be around hiding and keeping an eye on everything. They are then fed in the same place at the same time every day. We've had cats for years and years on the yard and this system has always worked. They do a great job with rats mice and rabbits. But we still feed them then they know this is their base. When they come the older ones are already spayed, and the CPL will always come back to catch the kittens when they are old enough to be spayed. They never become friendly but are sort of tolerant of our presence around the stables, but i suppose that's cats!