Tearing of the skin increases susceptibility to disease and may lead to cannibalism, with possible evisceration of the pecked bird and ultimately, death.
Risk factors that have been identified as increasing vent pecking include dim lights placed in nest boxes to encourage hens to use the boxes, the diet being changed more than three times during the egg laying period, the use of bell drinkers, and the hens beginning to lay earlier than 20 weeks of age.
[2] Vent pecking is associated with indicators of stress, e.g. fluctuating asymmetry, heterophil to lymphocyte ratio, and tonic immobility duration.
Mortality caused by cannibalism was reduced when hens had sufficient room to perch all facing the feed trough, thus giving their perch-mates little opportunity to peck at the vent region [9][10] and increased pecking activity and cannibalistic behaviour can occur due to inadequate height of the perches.
[11][12] Larger group sizes lead to increases in vent pecking[2][5] suggesting that social learning plays a role.