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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 |
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