Bone quality and composition are influenced by egg production, layer line, and oestradiol-17ß in laying hens.

ABSTRACT

Keel bone fractures are a serious animal welfare problem in laying hens. The aim of the current study was to assess the influence of egg production, oestradiol-17ß, and selection for high laying performance on bone quality. Hens of two layer lines differing in laying performance (WLA 320 eggs per year, G11 200 eggs per year) were allocated to four treatment groups. Group S received a deslorelin acetate implant that suppressed egg production. Group E received an implant with the sexual steroid oestradiol-17ß. Group SE received both implants and group C did not receive any implant. In the 63rd week of age, composition and characteristics of the tibiotarsi were assessed using histological analysis, three-point bending test, thermogravimetric analysis, infrared spectroscopy, and two-dimensional X-ray diffraction, respectively. Non-egg-laying hens showed a higher total bone area and a higher relative amount of cortical bone compared to egg-laying hens. Hens of layer line G11 showed a higher relative amount of medullary bone and a higher degree of mineralization of the cortical bone compared to hens of layer line WLA. These differences in bone composition may explain different susceptibility to keel bone fractures in non-egg-laying compared to egg-laying hens as well as in hens of layer lines differing in laying performance. The effect of exogenous oestradiol-17ß on bone parameters varied between the layer lines indicating a genetic influence on bone physiology and the way it can be modulated by hormone substitution.