A study by the Agricultural and Food Research Council in 1992 found that one-third of laying hens in cages suffered broken bones by the time of slaughter. The high incidence of broken bones is a severe welfare problem causing considerable pain and distress to birds. Most bone fractures occur when the hens are removed from cages and transported for slaughter. Bone fractures also occur when hens are disturbed. Because of their barren and monotonous surroundings battery hens are easily startled and are prone to hysteria.
Hens become frantic and try to flap their wings and hide at the rear of their cages.
This can spread through whole sheds and lead to a high incidence of injuries. Disease can also be a problem in battery farms. Infectious bronchitis, cage layer fatigue, leukosis and egg peritonitis are just some of the diseases prevalent in battery systems. Many hens are infected with salmonella and campylobacter though they may not show any symptoms. This can cause severe food poisoning in humans following consumption of contaminated eggs.