Abstract
Abnormalities in bone development in humans and non-humans can lead to impaired physical and psychological health; however, evidence is lacking regarding the role of individual psychosocial factors in the development of poor bone conditions. Addressing this lack of knowledge, we used low-productive laying hens (n = 93) and assessed behavioral responses to an open-field test [at 17, 18, 29, 33 weeks of age (wa)], an aerial predator test (at 39 wa), and a social reinstatement test (at 42 wa). Bone condition was assessed using a palpation technique on five occasions (at 16, 29, 33, 45, 58 wa), with half of the hens experiencing damage (deviations, fractures, or both) at 29 wa and all hens by 58 wa. Corticosterone (CORT) concentration in feathers (at 16, 33, 58 wa) and body weight (at 23, 47, 58 wa) were also investigated. We hypothesized that lighter birds (at 23 wa) with higher CORT (at 16 wa) and open field-induced fear collected before the onset of lay (at 17 and 18 wa) are associated with a worse bone condition when in lay. We also hypothesized that those birds with more damage at the peak of laying (at 29 wa) would be lighter at 47 and 58 wa and more fearful by showing higher open field-induced (at 29 and 33 wa) and predator-induced fear responses, however, acting less socially toward conspecifics. These hens were also expected to have higher CORT (at 33 and 58 wa). Our results show no association between open-field fear level and fear behavior, CORT concentration, or body weight on the one hand (all measured before starting to lay) and bone damage at 29 wa on the other. When in lay, bone damage was associated with more pecking and less crossing zones when faced with an open-field situation at 29 wa and improved sociality at 42 wa. This study provides the first evidence of a relationship of bone health with fear, sociality, and stress response. When in poor bone condition, our hens had enhanced psychological stress measured by fear behavior reactivity but not physiological stress measured as feather CORT concentration.
Highlights
Bone disease, such as osteoporosis in humans, is often seen as a silent disorder until it causes fractures [1]
Using the LOGISTIC procedure with modeling probability that keel bone damage (KBD) is 1, we investigated if the average fear score at (OFT1) and wa (OFT2) and fear-related behavior responses in OFT1 and OFT2, body weight at 23 wa, and CORT at 16 wa affected KBD
Consistency for reaching the central zone was lower than consistency for leaving the start box, with higher values in the rearing and laying period separately compared to the inclusion of all four repetitions of open-field test (OFT)
Summary
Bone disease, such as osteoporosis in humans, is often seen as a silent disorder until it causes fractures [1]. Many humans who suffer from bone fractures experience significant pain and weight loss; they may lose the ability to stand and walk [2] or may be immobilized by a fear of falling [3] or even begin to feel isolated and helpless [2]. On top of these effects, an increase in indirect costs [e.g., lost productivity for patients and caregivers [2] and increased stress level [4]] has recognized. Only recently has research intensively focused on looking at the underlying causes and consequences of KBD in commercial laying hens
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