We used to have quite a number of feral cats on our farm. We were able to trap and spay/neuter all of them eventually by feeding them in the traps for weeks before we actually sprung them. One of the ferals is our barn cat; I don't know what happened to the others; we continued to feed them, and they looked to be in good health, but they gradually vanished over time - coyotes, owls, other predators?