The air in the sheds is high in ammonia from bird feces, which are usually allowed to pile up for months and in some cases for a year or more before being cleaned out.

They are bred to have voracious appetites and gain weight as fast as possible, then reared in sheds that can hold more than 20,000 birds. The level of ammonia in the air from their accumulated droppings stings the eye and hurts the lungs.