Overcrowding of housed farm animals
Inadequate lighting in factory farming units
Due to the closely confined conditions of factory farming units, some animals die of stress from overcrowding. Productivity under stress tends to be less. Cannibalism increases in overcrowded conditions, particularly with hens.
According to behaviour studies, the optimum space allowance per hen is 750 sq cm. This is often not reached: average allowance in practice is 450 - 550 sq cm. Hens are often crowded together 4 or 5 to a cage, though 3 hens kept in a 4-hen cage produced 35 extra eggs each per laying season. A pronounced drop in efficiency has been noted among pigs kept under extreme conditions of intensive farming. Debeaking and dim lighting are used to check cannibalism among chickens in overcrowded pens, but not always with success.