Moh Sallam ¹ Lina Göransson ² Anne Larsen ² Wael Hamid ¹ Martin Johnsson ¹ Helena Wall ³ Dirk-Jan De Koning ¹ Stefan Gunnarsson ^2*

• ¹ Swedish University of Agricultural Sciences, Uppsala, Sweden
• ² Department of Applied Animal Science and Welfare, Swedish University of Agricultural Sciences (SLU), Skara, Sweden
• ³ Department of Applied Animal Science and Welfare, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden

Keel bone damage, include deviations and fractures, is common in both white and brown laying hens, regardless of housing. Radiography for assessing keel bones was proposed by previously, although it show only 2 dimensions. This study aimed to 1) investigate the association of radiographic optical density (keel and tibiotarsal) and keel geometry with dissected keel bone pathology. Previous studies suggested that keel bone fractures may result from internal pressure exerted by pelvic cavity contents. This study also aimed to 2) investigate the potential associations between pelvic dimensions and keel bone damage. A sample of 200 laying hens on a commercial farm were radiographed at 16, 29, 42, 55, and 68 weeks of age (WoA), and culled at the end of lay (74 WoA). The birds were examined post-mortem for pelvic dimensions and underwent whole-body radiography, followed by keel and tibiotarsal bone dissection and radiography, and keel bone scoring. The radiographs were used to estimate radiographic optical density (keel and tibiotarsal bone) and keel bone geometry. The method, included live bird restraint, positioning for live keel imaging, and image measurements, and was found to be reproducible. The radiographs (1,116 images of 168 birds) and the respective measurements and post-mortem scores of keel bones were also provided for further development. Some longitudinal radiographic measurements of keel geometry and optical density (keel and tibiotarsal) were associated with the damage observed in dissected keel bones. The associations of keel damage were clearer with the keel geometry than with keel and tibiotarsal optical density, also clearer for the keel deviations than for keel fractures. The higher radiography ratio of keel length to mid-depth at 42, 55 and 68 WoA the larger deviations size observed on the dissected keels. The higher the tibiotarsal radiographic optical density at 55 WoA, the lower deviations size and fractures count were observed on the dissected keels. Pelvic dimensions showed a positive correlation with body weight, but a larger pelvic cavity was associated with increased keel bone damage. These findings lay the foundations for future use of on-farm radiography in identifying appropriate phenotypes for genetic selection for improved keel bone health.