Broiler chickens are reared to provide chicken meat. The vast majority are kept in dimly lit, windowless sheds where they are packed so tightly that when fully grown you can often not see the floor. This is twice as fast as 30 years ago.
Fast growth has serious effects on their health and welfare.
The broiler chicken's muscle growth is very fast. However, the skeleton grows at a slower rate. Because of this, the birds' legs may not be able to support its body. By the time they reach slaughter weight some may have difficulty walking or reaching food and water. This can result in chickens dying of heart failure at very young ages.