The Effect of Photoperiod Length on Performance Parameters, Carcass Characteristics and Heterophil/Lymphocyte-Ratio in Broilers

This study was conducted to assess the effects of photoperiod length [Continuous lighting (24L:0D): 24 Lightness: 0 Darkness; Constant lighting (16L:8D): 16 Lightness:8 Darkness; Self-photoperiod (SP): 24 Lightness: free choice Darkness] on the performance, carcass characteristics and heterophil/lymphocyte ratio of male broilers grown to 42 d of age. A total of 180 Ross 308 males were exposed to one of the three lighting programmes: 16L:8D; 24L:0D and SP. In the self-photoperiod group, the percentage of animals that preferred to use the dark chamber, progressively increased throughout the trial. Starting from the 2nd week till the end of the trial, the live weights of the animals included in the 24L:0D and self-photoperiod groups were higher than those included in the 16L:8D group (P<0.01). The trial groups did not differ from each other for the end-trial feed consumption and feed conversion rates (P>0.05). No difference was detected between the groups for mortality rates or carcass percentages (P>0.05). The heterophil/lymphocyte ratios (H/L) were similar in the self-photoperiod and 16L:8D groups and were lower than those of the 24L:0D group. In conclusion; when the broilers allowed to regulate their own photoperiod, they had similar body weights but lower stress level than those kept under commercial lighting system.