Graded levels of Bactofort® modulates tonic immobility and behavioral vigilance responses of broiler chickens during the cold-dry (Harmattan) season

Abstract

The aim of the study was to determine the effect of graded levels of Bactofort® administration on tonic immobility (TI) and behavioral vigilance responses in broiler chickens during the cold-dry season. Complete randomized sampling was used to assign 300 broiler chicks into five groups. Each treatment was replicated three times, each having 20 birds. Group I served as control and were fed a basal diet without Bactofort® supplementation, group II were fed 0.25 g of Bactofort® per kg of feed, group III were fed 0.35 g of Bactofort® per kg of feed, group IV were fed 0.45 g of Bactofort® per kg of feed, and group V were fed 0.55 g of Bactofort® per kg of feed. Beginning from day-old, broiler chickens in the treatment groups were fed with Bactofort® supplementation daily for 6 weeks. TI was induced by manual restraint and vigilance elicited at self-righting graded for two days, two weeks apart, in 15 labeled broiler chickens from each of the five groups, at 06:00 h, 13:00 h, and 18:00 h, at 28 and 42 days. Each broiler chicken was laid on its back in a U-shaped cradle, covered with cloth. Dry-bulb temperature, relative humidity (RH) and temperature-humidity index inside the broiler chickens' house were recorded, concurrently during the TI and vigilance tests. The mean dry-bulb temperature and temperature-humidity index values fluctuated significantly (P < 0.0001 and P < 0.0001) as the hour of the day increases, with peak values of 35.53 ± 0.25 °C and 34.52 ± 0.17, recorded at 13:00 h, respectively. The RH fluctuated significantly (P < 0.0001) between 42 ± 1.81 % recorded at 13:00 h and 70.17 ± 2.39 % obtained at 6:00 h. There was significant increase in induction trial attempts from group I (control) to group V (0.55 g/kg) at day 28 (F4, 210 = 599.3; P < 0.0001) and 42 [(F 4, 210) = 434.6; P < 0.0001] in the treatment groups. The longest duration of TI and behavioral vigilance were recorded at 18:00 h for the control group. The shortest duration of TI and behavioral vigilance was obtained at 18:00 h in group V given 0.55 g/kg of Bactofort®. There was a gradual decrease in the duration of TI (F4, 435 = 12.16; P < 0.0001) and behavioral vigilance (F4, 435 = 56.88; P < 0.0001) in the treatment groups. The results demonstrate that the administration of graded levels of Bactofort® minimized the effect of stressful conditions on the broiler birds, as evidenced by shorter TI duration and decreased behavioral vigilance in the treated groups. In conclusion, the administration of Bactofort® mitigates the adverse effect of heat stress by decreasing TI and behavioral vigilance. The use of Bactofort® supplementation especially at 0.45-0.55 g of Bactofort® per kg of feed may improve the welfare and health of broiler chicken during the cold-dry season.