The role of retinal and extra-retinal photostimulation in reproductive activity in broiler breeder hens

Photostimulation of retinal photoreceptors, which are sensitive to green light, appears to inhibit reproductive activity in birds, whereas photostimulation of extra-retinal photoreceptors, which are sensitive to red light, accelerates it. The objective of this study was to determine the effect of either retinal or extra-retinal photostimulation on reproductive activities of broiler breeder hens. At 23 wk of age, Cobb hens (N = 135) were divided into 9 rooms with individual cages (n = 15). At 24 wk of age, 3 rooms were photostimulated (14L:10D) with white light (Control, n = 45). Six rooms had 2 parallel lighting systems, red (660 nm) and green (560 nm), which were both on during 6 out of 14 h of the light period. Then, in 3 of these rooms, the green light was turned off and hens were exposed to a total of 14 h of red light (Red, n = 45), and in the other 3, the red light was turned off and green lighting continued for a total of 14 h (Green, n = 45). The Green group had reduced egg production; reduced plasma concentrations of ovarian steroids; reduced luteinizing hormone (LH)-β, vasoactive intestinal peptide (VIP), and prolactin mRNA expression; and greater retinal green opsin mRNA expression ( P ≤ 0.05). The Red group had greater egg production; greater gonadotropin-releasing hormone-I (GnRH-I) and red opsin gene expression in the hypothalamus; and lesser green opsin gene expression in the retina ( P ≤ 0.05). We suggest that selective photostimulation of extra-retinal photostimulation as opposed to retinal photostimulation is a key factor in the determination of successful reproduction of broiler breeder hens.