Abstract
This work reviews the influence of production systems, strain and age of laying hens on keel bone damages (KBDs) with the subsequent welfare implications and production losses. Damages to the keel bone are influenced to a greater extent by the type of production system and its complexity. Hens housed in cage-free production systems are more likely to have a higher prevalence of this pathological condition than hens housed in cages. The aviaries, especially multi-tier, are more associated with this pathological condition. Clumsy ascents or descents from perches and collisions during flight with objects in the poultry house are other factors influencing the risk of KBD. However, the strain and age of hens may also cause a variation in damages incurred by the keel bone with older hens more prone to KBD(s) than younger hens. Damages to the keel bone have a significant effect on the growth, production, behavioural and welfare performance of laying hens. The mobility of hens with KBD is more likely to be impaired leading to lower feed intake, egg production and poor eggshell quality. Hens with KBD may experience failure to reach nests, which may increase the number of floor eggs and microbial contamination of eggs. The effective use of perches and pop-holes (in free range) may be limited among hens with severe damage to the keel bone. Hens with KBD may experience severe pain and discomfort leading to several hormonal and haematological changes. Impaired mobility may increase the time spent lying on litter substrates and thereby risk further damage to their feather and increase the risk of bumble foot/footpad dermatitis and breast blisters.