We have had a steady run of good mousers and there is this line with cats that we have yet to cross. The unfixed cat. While it would be far easier to allow the cats to breed in order to keep a steady supply, you just can't talk them into birth control.

A good friend of mine has a herd of unfixed cats, and he has no mouse problems, but now has cat problems. Especially if the rodent population is low, the cats, feral, will become quite mean and unapproachable. This is not so bad, and still a problem of its own dimensions.

The other part about the farm cats breeding on their own, they will attract predators and they will be killed off. The male urine is quite stinky and attracts other feral cats. This process is noted by nearby predators and will increase the visitation of certain predators, at which time there comes the need for more dogs and donkeys.

So, while it is a possibility, it is remote for now.