Genetic variation of keel and long bone skeletal properties for five lines of laying hens

Summary Fractures to the keel bone is one of the greatest problems facing the laying hen industry. With most severe effects observed in non-cage housing, frequencies are expected to dramatically increase as the industry continues transitioning away from battery cages. Incidences within commercial systems are well documented where the main cause is believed to be high egg production and the associated need for calcium drawing on endogenous reserves (i.e., bone) leaving bone weakened and prone to fracture. The current work sought to characterize various bone mineral and biomechanical properties of five distinct purebred/crossbred laying hen lines (three commercial: Bovans Brown, Dekalb White and ISA Dual Brown; two non-commercial: Experimental Brown, Experimental White) following previous work that demonstrated differences in susceptibility to keel fracture using an ex vivo impact testing apparatus. The keel was then removed to undergo analysis by computer tomography; the humerus and tibia were also removed for biomechanical testing. The keel bone mineral density and moment of area correlated moderately with hen weight and susceptibility to fracture. The biomechanical properties of the tibia, but not the humerus, showed a strong relationship with hen weight. One commercial genetic line (Dekalb White) with a high susceptibility to fracture exhibited a mean tibia strength below the value expected from its mean weight. Our results suggest that for the purebred/crossbred lines other than Dekalb White, rather than properties of bone, lower mean weight may imply higher levels of activity, higher risk of collisions and lower soft tissue protection that reflect greater susceptibility to keel fracture.