Associating maternal keel fracture severities with egg quality, hen reproductive outcome, and chick welfare

Maternal conditions are known to affect offspring behavior and performance in laying hens. With evidence suggesting that keel fractures cause pain and may lead to stress and fear in affected hens, this study hypothesized decreased egg quality, reproductive outcomes, offspring chicks’ weight, and increased fear responses in the chicks as keel fracture severity increased.

120 Bovans brown layer breeders aged 61 weeks, with different keel fracture severities, were co-housed with 12 cocks at 20 hens+2 cocks/room. Eggs laid between weeks 65-70 were collected either for incubation or egg quality assessments. At week 70, 111 hens were euthanized, keel bones were dissected and scored (0:no fracture, n = 21; 1:slight fracture, n = 25; 2:moderate fracture, n = 29; 3:severe fracture, n = 36). Majority of the fractured hens (88 out of 90) presented hard callus without fracture gaps, suggesting healed fracture status. At hatch, 612 chicks were generated. Chicks’ body weight was measured weekly until week 5. All chicks were subjected to tonic immobility (week four) and novel arena tests (week five).

Dry shell weight was lower for moderate (P = 0.007) and severely (P < 0.001) fractured hens, while eggshell index was lower in severely fractured hens (P < 0.001) compared with those without fractures. Shell thickness decreased as fracture severity increased (P < 0.001). Overall, egg-breaking force was lower (P < 0.001) among fractured hens, but there was no difference in breaking force of the three fracture severity groups. Lower hatch rate was recorded in moderate (P = 0.038) and severely (P = 0.003) fractured hens compared with those without fractures. Irrespective of severity, chicks from fractured hens had lower odds (P < 0.05) of performing escape attempts, higher likelihoods (P < 0.001) of freezing and sitting inactive.

In summary, layer breeders with moderate and severe fractures, even after healing, produced eggs with lower shell quality, breaking strength, and hatch rate. At higher prevalence, this may have implications for the managerial practice and economic return of a breeder flock. Maternal keel fracture was associated with altered fear behavioral patterns in chicks, with a shift from active to passive responses.