Actually, commercial chicken keepers make tremendous efforts to keep their birds healthy and adopt very stringent biosecurity protocols -- to the point that if you work on a commercial chicken farm you are not permitted to own poultry at home.
There are a lot of people who are either emotionally or financially invested in spreading horror stories about commercial poultry, but the idea that birds are being abused is SILLY.
Only a complete idiot would mistreat the animals upon which his life and livelihood depend -- even if only for financial reasons because a mistreated animal is an unproductive and unprofitable animal.