Effects of Photoperiod on the Performance, Blood Profile, Welfare Parameters, and Carcass Characteristics in Broiler Chickens

SIMPLE SUMMARY: The physiology and behavior of birds, including poultry, are greatly affected by light. The poultry industry uses lighting regimens with long lighting periods to maximize the growth of broiler chickens. Rapid growth not only adversely affects the health of the birds, but also causes great stress. As animal welfare issues have become increasingly important, concerns regarding the current photoperiods in broiler production have increased. In this study, the effects of the photoperiod on the productivity and various welfare indicators on broiler rearing were investigated. Generally, the productivity and stress of broilers were both positively and negatively correlated with the photoperiod. The results showed that a photoperiod of 18L:6D was appropriate, when considering the growth and stress of broilers. The optimum photoperiod for broilers may vary in different feeding phases, with respect to performance and welfare. Therefore, continuous research is needed to establish the ideal light regimens under the consideration of the productivity and welfare of broilers. ABSTRACT: We studied the effects of photoperiods on the growth performance, blood profile, welfare parameters, and carcass characteristics of broilers. A total of 336 male broiler chicks (Ross 308) were randomly allocated into 4 treatments (84 birds per treatment with 4 replicates), based on the following lighting regimen: 24 h continuous light (24L), 18 h continuous light (18L:6D), 8 h continuous light (8L:16D), and intermittent light (4L:2D). Body weight and feed intake of 7- and 35-day-old broilers were measured. At 5 weeks of age, 12 birds per treatment were selected for blood collection and carcass analysis. Body weight, body weight gain, and feed intake were the lowest in the 8L:16D treatment (p < 0.05). The heterophil-to-lymphocyte ratio, aspartate aminotransferase, interleukin-6, and corticosterone levels in the 24L treatment increased significantly when compared to that in the 18L:6D treatment (p < 0.05). The footpad dermatitis score was significantly lower in the 18L:6D and 8L:16D treatments than in the 24L and 4L:2D treatments (p < 0.001). There was no significant difference in the carcass and meat characteristics, except for the shear force of breast meat (Pectoralis major), which was the lowest in the 8L:16D treatment (p < 0.05). These results indicate that a photoperiod of 18 h resulted in an improvement in the performance and welfare of birds and a simultaneous decrease in stress level. However, further research is needed to establish a lighting regimen that satisfies both the productivity and welfare requirements of broilers in different feeding phases.