Barn cats can be a treasured benefit to help control rodents, which keeps your family and farm animals healthy. Rodents have been around since farming began and cats are the first line of defense. Rodent droppings can contain salmonella which can infect the farm animals, then cause illnesses in people when the meat or eggs are consumed. People can become infected when they breathe air that has been contaminated with the Hantavirus virus from rat urine. Rodents that have fleas can carry Lyme disease. Therefore you need to keep barn cats healthy which includes; fresh water, safe shelter and have them spayed or neutered. Vaccinating your barn cats protects them from illnesses: cats that eat rodents are susceptible to intestinal parasites; feline leukemia virus and feline immunodeficiency virus are among the most lethal feline diseases. Infected cats don’t always show symptoms yet can easily spread the diseases. Feral and stray cats that are not suited for indoor life as pets make excellent barn cats.
https://www.linkedin.com/pulse/long-live-barn-cat-randy-bilesky?published=t
http://www.delta-optimist.com/opinion/blogs/blog-long-live-the-barn-cat-1.2184477