Evaluating perching biomechanics in commercial and random-bred strains of enriched-housed laying hens
Creators: DePaoli, Emily C.R.M.
Publisher: name: University of Alberta Library
Year: 2023

<p>Housing, including rearing environment and provided enrichments, impact the welfare of laying hens throughout their life. As the Canadian egg layer industry shifted away from conventional cages, an increase in keel bone damage (KBD) has raised welfare and economic concerns. Keel bone damage leads to reduced egg production, reduced egg quality, and negative affective states due to pain in laying hens. Our understanding of the genetic and environmental components that impact KBD is limited. The objective of our research was to identify genetic and environmental factors that contribute to KBD in enriched housed laying hens to help reduce the incidence below levels traditionally seen in conventional housing.<br>
In our first study, commercial strains (Lohmann White, Shaver White, Lohmann Brown, ISA Brown) and random-bred strains (Shaver Rhode Island Red and Antique White Leghorn) were studied (n=20/treatment) to determine the impact of strain and perch shape (mushroom or round) on innate perching biomechanics at pre, peak, and end of lay, and secondly how strain affects KBD, body weight, footpad temperature, and bone composition. Perching kinematics, footpad temperature, bone parameters (femur and keel bone mineral content and density), and KBD severity were assessed. In addition, genotyping was conducted on tissue samples collected postmortem to identify causative mutations that negatively impact bone parameters. Single-SNP associations between bone parameters and SNPs located on candidate genes (RANKL, RB1, SOST, POSTN, SOX9, PTHLH, OVALX) were assessed. Rhode Island Red had greater femur bone mineral density and content than all other strains. Higher producing commercial strains had higher incidences of severe KBD. Round perches led to faster forward and backward and up and down movements compared to mushroom perches. Commercial strains moved up and down more and forward and backward less than random-bred strains. Up and down movements were correlated with higher incidences of severe KBD. Strain, but not perch shape, significantly impacted footpad temperature. Overall, round perches contributed to perching instability and random-bred and commercial strains had fundamentally different movement patterns while perching. Seven SNPs segregated and significant SNP effects on bone parameters from RANKL, RB1, POSTN, and OVALX genes were located, however, SNP effects were confounded by significant strain effects.<br><br>
In our second study, we aimed to determine which strains experience certain perching biomechanics, higher bone strength, and keel health within enriched housed layers depending on perch design and pullet rearing system used. Lohmann White and Lohmann Brown pullets were placed in either pullet cages or floor pens at hatch with access to mushroom or round perches (n=9/treatment) and were transferred to an enriched battery at lay. Perching kinematics, body weights, bone parameters (femur and keel bone mineral content and density), bone breaking strength, and keel scores were evaluated. Behaviour observations were conducted every two weeks from seven until 69 weeks of age. Lohmann Brown spent more time perching from two to six months of age, when the keel is more susceptible to damage. There was a positive correlation between severity of deviation present and forward and backward keel motion. Keel and femur bone strength, content, and density were higher in Lohmann Brown in comparison to Lohmann White. Measured bone parameters were not protective against severe KBD as Lohmann Brown had more severe deviations and more fractures than Lohmann White. Round perches led to more severe KBD in comparison to mushroom perches. Increased forward and backward movements exhibited by Lohmann Brown were correlated with more severe KBD. <br>
In conclusion, up and down movements and forward and backward movements correlated with a higher incidence of severe KBD. Mushroom perches are preferable to round perches for laying hens housed in furnished cages due to reduced KBD and increased stability while perching. Lower incidences of KBD despite lower bone mineralization indicate LW birds are more readily suited to furnished cages in comparison to LB birds. Higher producing, commercial strains had higher incidences of severe KBD. POSTN, RANKL, RB1, and OVALX are promising candidate genes for locating SNPs associated with bone parameters in laying hens. </p>