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Keel bone damage may be painful to birds and affect their production. In order to better understand the frequency, position, and timepoint of keel bone damage that occur during production, the integrity of W-36 laying hen keel bones housed in enriched colony cages at 748.4 cm2 (116 in2) was evaluated. At four time points, 120 birds (10 per cage; three cages per each of four rooms) had keel bones evaluated. Each hen was placed in a motion limiting restraint, scanned using computed tomography (CT), fitted in vests containing tri-axial accelerometers, and placed back in their cages for 21 d. After 21 d, the hens were rescanned and returned to their cages. This process was repeated after 133 d. The CT scans were imported into Mimics analysis software (Materialise, Plymouth, MI, USA); 3D models were made of each keel bone at each time point and exported to 3-matic analysis software (Materialise, Plymouth, MI, USA). Each laying hen's keel bone model was superimposed onto scans from multiple time points resulting in four bone pairings representative of each 21-d period, the 133-d period, and the entire duration of the project. Next, the proximal portion of each bone pairing was edited to normalize bone shape according to a strict protocol. Additionally, each pairing was divided into three portions: distal aspect (3 cm), proximal aspect (2 cm), and middle portion (remaining). Whole bone pairing and each bone portion was analyzed using the Part Comparison tool in 3-matic. Raw data were compiled into three datasets and analyzed in SAS 9.3 using the GLIMMIX procedure using a three-level random intercept model. The model controlled for time, part, part(time), and system with random intercepts of bird(cage) and cage. Overall, results revealed that the greatest morphological changes occurred during the first 21-d period with regards to time (P = 0.03) and in the distal aspect of the keel with regards to part (P < 0.0001). [ABSTRACT FROM AUTHOR]

• The structures of acceleration events experienced at the keel were described. • Acceleration events occurred mainly when hens collided with their environment. • Collisions typically occurred when hens attempted to ascend onto a perch. Factors contributing to the development of keel bone damage are not well understood. This study aimed to identify behaviors and cage structures associated with acceleration events experienced by individual hens at their keels as the birds navigated their enriched colony cage environments. Additionally, we aimed to characterize the accelerations associated with these behaviors, as we postulated that behaviors associated with higher accelerations may be more likely to lead to keel bone damage. Sixty five 19 week old Hyline W36 hens were placed in each of 12 enriched colony cages. Ten focal hens per cage were selected for observation. Each hen was fitted with a jacket which contained a tri-axial accelerometer with an external sensor that was fitted into a small pocked over the hen's keel. The logger recorded any time that the hen sustained an acceleration event at the keel (>12 G-units). Logger output was matched with video data, allowing us to describe the behavior of the affected bird at the time of the acceleration event recorded at the keel. Data on each bird were collected continuously over two 3-week periods, when the hens were between 52–60 and 74–83 weeks of age. Collisions accounted for nearly 81% of observed acceleration events with acceleration peaks of at least 20 G-units. The majority of collisions were with the perch and were sustained mainly as the hen attempted to ascend onto it. It has previously been reported that the prevalence of keel bone fractures is higher among hens housed in cages that do versus do not contain perches. This study lends support to the growing body of evidence indicating that interactions with perch contribute to the keel bone damage sustained by laying hens housed in enriched colony cage systems, however, the relationship between acceleration events and occurrence of keel bone damage has yet to be directly assessed. [ABSTRACT FROM AUTHOR]