Abstract
The aim of the experiment was to evaluate effects of zinc gluconate (ZnGlu) and probiotic administration on the daily rhythm of cloacal temperature (t(cloacal)) in broiler chickens of different age groups during the hot-dry season. One-day-old broiler chicks (n = 60) were divided into groups I-IV of 15 chicks per group, and treated for 35 days: Group I (control) was given deionized water; Group II, ZnGlu (50 mg/kg); Group III, probiotic (4.125 × 10(6 )cfu/100 mL), and Group IV, ZnGlu (50 mg/kg) + probiotic (4.125 × 10(6 )cfu/100 mL). Air dry-bulb temperature (t(db)), relative humidity (RH), and temperature-humidity index (THI) inside the pen, and t(cloacal) of each broiler chick were obtained bihourly over a 24-h period; on days 21, 28, and 35 of the study. Values of t(db) (32.10 ± 0.49°C), RH (49.94 ± 1.91%), and THI (38.85 ± 0.42) obtained were outside the thermoneutral zone for broiler chickens, and suggested that the birds were subjected to heat stress. Application of the periodic model showed disruption of daily rhythm of t(cloacal) in broilers on day 21, which was synchronized by probiotic administration. The administration of probiotics or ZnGlu + probiotics to a greater extent decreased the mesor and amplitude, delayed the acrophases of t(cloacal) in broilers, especially at day 35, as compared to the controls. Overall, the t(cloacal) values in broiler chickens administered with probiotic alone (41.25 ± 0.05°C) and ZnGlu + probiotic (41.52 ± 0.05°C) were lower (P < 0.001) than that of the controls (41.94 ± 0.06°C). In conclusion, probiotic alone synchronized t(cloacal) of the birds at day 21, and, in addition, decreased t(cloacal) response most, followed by its coadministration with ZnGlu, the antioxidants may be beneficial in modulating daily rhythmicity of t(cloacal) and alleviating adverse effects of heat stress on broiler chickens during the hot-dry season.