Keel bone damage (KBD) is more prevalent in alternative laying hen housing systems than in conventional cages, and its incidence differs from strain to strain. However, the information of KBD in Lindian chickens, a native Chinese strain, is limited. To investigate the effect of KBD on fearfulness and physiological indicators of stress in Lindian chickens and commercial laying hens, a total of two hundred 25-wk-old chickens (100 Hy-line Brown and 100 Lindian chickens) were studied for 7 wk. The birds were housed in furnished cages with 10 birds per cage for each strain. At 32-wk of age, the birds in each strain were divided into normal (NK), deviated (DK), and fractured (FK) hens according to the keel bone status. Ten birds in each keel bone status per strain were subsequently selected to collect blood for the determination of stress and fear-related indicators, including corticosterone, serotonin, interleukin-1β, and interleukin-6, and measure fear responses, including novel object test (NOT), human approach test (HAT), and tonic immobility (TI) test. The results showed that egg production was lower and the incidence of keel bone fractures was higher in Lindian chickens than in Hy-line Brown hens (P < 0.05). Lindian chickens showed a significantly increased whole blood serotonin content, NOT-latency, HAT-score, and TI induction times (P < 0.05) and decreased serum interleukin-6 content and TI-duration (P < 0.05) compared with Hy-line Brown hens. Additionally, FK hens had significantly elevated whole blood corticosterone, serum interleukin-1β and interleukin-6 levels, TI-duration, and NOT-latency (P < 0.05), and a reduced whole blood serotonin content (P < 0.05) compared with NK and DK hens. Our results indicated that KBD affected stress and fear responses, and this impact was mainly reflected by FK hens compared with NK and DK hens. We suggest that keel bone fractures are the main factor impairing hen welfare. Besides, the incidence of keel bone fractures and stress and fear responses of Lindian chickens are more severe than Hy-line Brown laying hens, indicating that the strain type can affect the health and welfare of laying hens.
Keywords: fear; keel bone fracture; laying hen; stress; welfare.
Keel bone damage (KBD) impairs production performance, welfare, and health in laying hens. This study aimed to compare the incidence of KBD and investigate the effects of KBD on stress and fear in two strains of laying hens. The results showed that commercial Hy-line Brown laying hens had high egg production and low incidence of KBD compared with Lindian chickens, a Chinese native breed. Besides, Lindian chickens had higher blood serotonin content and fear responses to human approach test and novel object test than Hy-line Brown laying hens. In addition, laying hens with keel bone fractures had elevated concentrations of blood corticosterone, interleukin-1β, and interleukin-6, and had a longer duration of tonic immobility and latency to approach a novel object, as well as reduced blood serotonin content compared with laying hens with normal and deviated keel bone. Overall, keel bone fractures caused stress and fear responses, impairing hen welfare; and behavioral and physiological responses in relation to stress and fear differed between strains of hens.
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