Abstract
Keel bone damage is an important animal welfare problem in laying hens. Two generations of four layer lines, differing in phylogenetic background and performance level and kept in single cages or floor pens were weighed and scored for keel bone deformities (KBD) during the laying period. KBD, keel bone fractures (KBF) and the bone mineral density (BMD) of the keels were assessed post mortem. For BMD, relationships to laying performance and body growth were estimated. Caged hens showed more deformities, but fewer fractures and a lower BMD of the keel bone than floor-housed hens. White-egg layers had a lower BMD (0.140-0.165 g/cm2) and more KBD than brown-egg layers (0.179-0.184 g/cm2). KBF occurred more often in the high-performing lines than the moderate-performing ones. However, in the high-performing lines, BMD was positively related to total egg number from 18 to 29 weeks of age. The adult body weight derived from fitted growth curves (Gompertz function) had a significant effect (p < 0.001) on keels' BMD. The study contributes to the understanding of predisposing factors for keel bone damage in laying hens. It showed that the growth rate has a rather subordinate effect on keels' BMD, while the BMD itself greatly affects KBD.
Highlights
Keel bone damage is an important animal welfare issue, as an alarmingly high number of laying hens show keel bone deformities (KBD) and/or -fractures (KBF).keel bone damages are of economic importance
While KBD occurred significantly more often and more severe in hens of the white-egg layer lines compared to the brown ones at any time of examination within the cage system, in the floor housing system, the same trend was seen from the 29th week of age onwards, without reaching a significant value at any day of scoring
The study contributes to the understanding of predisposing factors for keel bone damage in laying hens
Summary
Keel bone damage is an important animal welfare issue, as an alarmingly high number of laying hens show keel bone deformities (KBD) and/or -fractures (KBF) (reviewed by [1]). Keel bone damages are of economic importance. KBF are often accompanied by a lower egg production [2,3] and poor egg quality including reduced shell thickness and breaking strength [4] as well as lower shell weights [2]. Chargo et al [5] attributed the decreased production to changes in the hens’ behavior due to pain or musculature changes as a result of keel bone damage. Keel bone damage is a complex trait and there are numerous factors, including nutritional, environmental and genetic ones, which influence the risk and possibility of developing such disorders [8]
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