Effect of Photoperiod on Physiological Parameters in Broiler Chicks from Placement to 7-days-of-age1,2

Photoperiod effects during the first 7 days post-hatch have not been adequately investigated for broiler chicks, especially with modern genetics. Acclimation to the rearing environment (location of feed and water) has historically been the impetus for continuous or near-continuous photoperiods for broilers during the first 7 days. However, recent research has shown that a shorter photoperiod initiated from the day of hatch (20L:4D) does not result in any significant differences in live performance (Crop fill, BW, BW gain, FI, FCR) compared to near-continuous lighting (23L:1D). Furthermore, excessive lighting during this critical developmental window may have detrimental physiological effects, which could ultimately inhibit full production potential and decrease overall health and welfare. This study examines the effect of a longer dark phase (scotophase) applied during the first 7 days post-hatch on physiological parameters (melatonin, blood glucose, corticosterone). A total of 176 Ross 708 broiler chickens were reared in two trials to 7 days of age using two different lighting program treatments (20L:4D vs 23L:1D) applied from day-of-hatch. Blood sampling was conducted at even intervals during the dark period at d 7. Melatonin production was significantly increased in the 20L:4D group, blood glucose levels maintained a consistent level throughout the dark period for the 20L:4D group, and corticosterone levels were not outside of the normal physiological range for either group. Increased scotophase length implemented as early as day-of-hatch may result in improved physiological function including growth, health indices, and productivity among others.