Steep sloping floors lead to high levels of foot deformities as birds are more likely to slip. Overcrowding means hens are unable to exercise. This results in weak, brittle bones which are prone to fracture. 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.