It's actualy not hormones as such, they add antibiotics to many feeds . They do it in the poultry, pork, beef and lamb industry, by maintaining small but constant levels it controls disease and promotes better yields ( larger animals ). The FDA in the US has of this year , banned the use of them , only hope we follow. The antibiotics that we use in sickness are becoming less and less effective because we are continually consuming them in our food chain. I've had to resort to organic chick starter here , because recently they removed the amprolium and replaced it with an antibiotic . So for many people they will be starting their chicks on antibiotics from day 1. 
