Until I read all the posts about chickens devouring mice and lizards I had no idea they did so. Of course, I'm well aware they provide wonderful insect control. For those of you who have mouse eating chickens, keep in mind that mice and rats frequently carry Salmonella. Rats frequently carry the organism that causes fowl cholera, Pasteurella multocida. So if you eat the eggs from the carnivourus chickens, cook the eggs thoroughly. For those of you participating in the NPIP, the birds that consume Salmonella contaminated rodents may test positive to Salmonella
If you use the chicken manure to fertilize your garden, realize you are probably spreading the Salmonella organism around. Wear gloves and wash your hands immediately after working with the Salmonella contaminated manure. When you harvest the garden's products, wash them thoroughly.
Water running across your chicken yard is probably picking up the organism and possibly contaminating a stream or pond.
So, chickens may provide good rodent control, but there are certainly ramifications to consider.