I've been catching lots of mice lately. Rather than throw them in the trash or otherwise try to get rid of them I've started giving them to my chickens. They seem to love them. As soon as the mouse hits the ground a chicken grabs it and runs off with it, with other chickens chasing along trying to steal it. Eventually the mouse gets pecked to pieces and eaten. It seems like an inexhaustible source of protein for the chickens, but there's got to be some down side of it, right? Like maybe parasites or diseases or something passing from the mice to the chickens?
As long as your coop is clean, and they aren't eating the droopings, I think they are fine. My birds will eat naything that doesn't eat them first! This year a little finch dropped down in the yard to eat and didn't see the big hen behind it! It was not a pretty sight! I would treat for parasites as usual. Worming twice a year is a good idea, and dusting with Sevin on first sign of mites. I really don't think there is a problem with them eating mice as often as they catch them!