Effect of pullet rearing environment, strain and perch shape on perching behaviour, perching biomechanics, and keel bone damage in enriched-housed laying hens

Abstract

Housing, including pullet rearing environment and enrichments, impacts the welfare of laying hens throughout their life. As the egg industry shifts towards alternative housing systems (furnished cages, aviary, free-run, and free range), an increase in keel bone damage has raised welfare and economic concerns. Keel bone damage leads to reduced egg production, reduced egg quality and pain in laying hens. Our study aimed to determine within enriched caged layers, which strains experience stable perching biomechanics, bone strength, and keel health depending on perch design and pullet rearing system used. A 2 ×2 ×2 randomized complete block design with repeated measures was used. Lohmann White or Lohmann Brown pullets were placed in either pullet cages or floor pens at hatch with access to either mushroom or round perches (n=9 replicates/treatments) and then transferred to an enriched battery at lay. Perching kinematics, body weights, and keel scores were evaluated every two months (2, 4, 6, 8, 10, 12, 14 and 16 months of age). Dual x-ray absorptiometry and bone breaking strength tests were used to assess femur and keel bone mineral content and density; keel bone damage severity was assessed via digital imaging post-mortem. 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 (r 0.24; P<0.001). All bone parameters were affected by strain. Keel and femur content (Femur 3.50 g; Keel 2.08 g; P<0.001), and density (Femur 0.23 g/cm2; Keel 0.10 g/cm2; P<0.001) were higher in Lohmann Brown in comparison to Lohmann White (Femur 0.18 g/cm2 and 2.60 g ±0.069; Keel 0.07 g/cm2 and 1.19 g). Measured bone parameters were not protective against severe KBD as Lohmann Brown had more severe deviations (P<0.01) and more fractures (P<0.01) than Lohmann White. Pullet rearing environment did not have any effect on keel bone damage scores (P>0.10). Round perches led to more severe KBD in comparison to mushroom perches (P<0.05). In conclusion, 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 Lohmann White birds are more readily suited to furnished cages in comparison to Lohmann Brown birds.