Effects of incubation lighting with green or white light on brown layers: hatching performance, feather pecking and hypothalamic expressions of genes related with photoreception, serotonin, and stress systems

The aim of this study was to evaluate the effect of 16L:8D photoperiod with green (GREEN) or white (WHITE) lights during incuba-tion on hatching performance, blood melatonin, corti-costerone, and serotonin levels, hypothalamic expressions of genes related to photoreception, seroto-nin, and stress systems in layers in relation with feather pecking behavior. Dark incubation (DARK) was the control. Eggs (n = 1,176) from Brown Nick breeders in 2 batches (n = 588/batch) were incubated in the exper-iment. A total of 396 female chicks and 261 hens were used at rearing and laying periods until 40 wk. Incuba-tion lighting did not affect hatchability, day-old chick weight, and length, but resulted in a more synchronized hatch as compared with the DARK. The effect of incu-bation lighting on blood hormones was not significant except for reduced serotonin in the GREEN group at the end of the experiment. There was no effect of incu-bation lighting on gentle, severe, and aggressive peck-ing of birds during the early rearing period. From 16 wk, GREEN hens showed increased gentle pecking with increasing age. WHITE hens had the highest gen-tle pecking frequency at 16 wk while they performed less gentle but higher severe and aggressive pecks at 24 and 32 wk. At hatching, the hypothalamic expression of CRH, 5-HTR1A, and 5-HTR1B was higher for the WHITE group compared with both GREEN and DARK, however, 5-HTT expression was higher in GREEN than WHITE which was similar to DARK. Except for the highest VA opsin expression obtained for WHITE hens at 40 wk of age, there was no change in hypothalamic expression levels of rhodopsin, VA opsin, red, and green opsins at any age. Although blood hormone levels were not consistent, results provide pre-liminary evidence that incubation lighting modulates the pecking tendencies of laying hens, probably through the observed changes in hypothalamic expres-sion of genes related to the serotonin system and stress. Significant correlations among the hypothalamic gene expression levels supplied further evidence for the asso-ciations among photoreception, serotonin, and stress systems.

Automated summary

This study aimed to evaluate the effects of different incubation lighting conditions on hatching performance, blood hormone levels, and hypothalamic gene expression in laying hens. Results showed that incubation lighting had an impact on hatching performance, feather pecking behavior, and hypothalamic gene expression, indicating a potential modulation of pecking tendencies in laying hens through changes in gene expression related to serotonin system and stress. However, there were no significant effects on gentle, severe, and aggressive pecking behaviors.