O. Distl

Keel bone condition in laying hens: a histological evaluation of macroscopically assessed keel bones.

The objective of the present study was to conduct a corresponding histological analysis of 162 macroscopically assessed keel bones (1: severe, 2: moderate, 3: slight, 4: no deformity). Four layer lines were used and hens were kept in furnished cages, small group systems (both allowing more activities due to the provision of perches) and an aviary system, which fully conformed to the EU standards. Investigations were carried out in the 3rd, 6th, 9th and 12th laying month of two experimental trials. In 97.9% of grade 4 keel bones, no histological deviations were found, whereas in keel bones manifesting deformities of grade 1 and 2, the predominant histological observation was the incidence of fracture callus material (FCM) and new bone in the form of woven bone. FCM was also detected in 50.9% of grade 3 keel bones, whereas in 40.7%, only s-shaped deviations of keel bones were found, which were related to extended pressure loading while perching activities rather than short-duration trauma. Histological analysis showed that keel bones of grade 1 and 2 were mainly attributed to traumatic origin and therefore associated with pain experience in layers. Grade 3 keel bones manifested either FCM as a result of trauma or adaptational deformities without any evidence of a preceding fracture in response to mechanical pressure loading and were most likely not associated with pain. Therefore, histological analysis was found to be a mandatory tool when evaluating grade 3 keel bones with respect to layerswelfare. Furthermore, this analysis corroborates the findings that in aviary systems deformities of keel bones are predominantly caused by painful fractures.

Bone strength and keel bone status of two layer strains kept in small group housing systems with different perch configurations and group sizes.

The objective of the present study was to investigate whether an arrangement of perches at two different heights within individual compartments of small group systems (back perch elevated (BE), front perch elevated (FE) or both perches heightened (FBE)) combined with an enlarged group size would increase humerus and tibia bone breaking strength and impact keel bone status. Bone strength and keel bone status of two layer strains (LSL, LB) kept in small group systems (SG 40-60 (40, 60 hens), SG 20-30 (20, 30 hens) with different perch configurations) and furnished cages (FC, 10, 20 hens, perches in standard position) were compared in two trials. Investigations were carried out in the laying months 6 and 12, comprising a total of 576 hens. When all compartments of SG 40-60 had been incorporated with perches at two different heights, humerus and tibia bone strength in LSL layers significantly increased compared to FC, whereas keel bone status was negatively impacted. Within SG 40-60, BE and FE perches significantly increased humerus strength in LSL layers compared to FBE perches. LB layers had significantly higher bone strength in groups of 20 compared to 30 hens in SG 20-30, whereas no effect of group size was detected for LSL hens. Keeping hens in SG 40-60 with modified perch positions was associated with increased bone strength but brought about the problem of inferior keel bone status.