ABSTRACT: In nature, animals are exposed to a single photophase (light period) and single scotophase (dark period) each day. Commercial broiler management practices often split the dark period to limit the time broilers are off feed, which results in two photophases and two scotophases per 24-hour period. In this study, we evaluated the effects of one or two light phases per day on the growth performance, feed intake, blood profile, activity, and behavioral parameters of broilers. We found that broilers show numerically increased weight and better FCR in the single photophase group compared to the dual photophase group. The single photophase schedule resulted in improvement of behavioral and physiological indicators of fear, stress, and welfare.
BACKGROUND
The Council of the European Union (2007) specifies that broiler chickens must be provided at least 6 hours of darkness during each 24-hour period. Due to the prolonged fasting induced by a 6-hour scotophase, lighting schedules are sometimes modified to split the scotophase into two parts. This results in two photophases and two scotophases per 24-hour day. Given the highly unnatural lighting schedule of a dual-photophase/scotophase program, the question has been raised whether dual photphase/scotophase lighting program negatively affects the circadian functioning and possibly productivity and welfare of the broiler chickens as compared to more natural single photophase/scotophase schedule.
METHODS
A total of 500 day-old Ross 308 chicks were randomly allocated into 2 treatment groups (250 birds per group with 5 replicate rooms each). Lighting schedules during brood were identical between the two treatments. On Day 6 post-hatch, the two lighting treatments were: single photophase, 16 hours light and 8 hours dark (16L:8D) and dual photophase, 8 hours light, 4 hours dark, 8 hours light, 4 hours dark (8L:4D:8L:4D). Body weight and feed intake were measured at 7, 15, 25, 33 and 42-days-old. At 6 weeks of age, the birds were evaluated for isolation vocalizations, inversion wing flapping, tonic immobility and emergence test. Blood was analyzed for Heterophil:Lymphocyte ratio (H:L) and for serum lactate concentration. Bird movement and audio activity was monitored and quantified throughout the trial.
RESULTS
The single photophase schedule resulted in numerically higher body weights (2.4%, p =0.15) and a lower feed conversion ratio (2.7 percentage points, p > 0.05 ) compared to the dual photophase schedule at 42 days post-hatch. Serum lactate was significantly reduced by 14% under the single photophase schedule (p=0.0008). H:L ratio was numerically 17% lower under the single photophase schedule (p=0.14). Inversion wing flapping was numerically reduced by 13% (p=0.09) under the single photophase schedule. Isolation vocalizations were numerically reduced 22% under the single photophase schedule (p=0.12). No trending differences were observed for time of emergence or tonic immobility between treatment groups.
Activity analysis (see figure below) showed that broilers exhibited more movement during the photophase than scotophase. In both treatment conditions, activity was highest shortly after the lights turned on and immediately before lights were turned off. The dual photophase group exhibited higher activity levels during the mid-day scotophase compared to the nighttime scotophase.
CONCLUSION
These results indicate that a single photophase lighting schedule may result in better performance and lower stress of broiler chickens than a dual photophase lighting schedule. Additionally, this study demonstrates that even during dual photophase schedules, the birds still maintain a different activity state during the mid-day scotophase compared with the subjective nighttime scotophase.