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 × 106 cfu/100 mL), and Group IV, ZnGlu (50 mg/kg) + probiotic (4.125 × 106 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 tdb (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 tcloacal and alleviating adverse effects of heat stress on broiler chickens during the hot‐dry season.
Highlights
The thermal environmental conditions during the hot-dry season in the Northern Guinea Savannah zone of Nigeria, which prevails from March to May (Dzenda et al 2011) induce heat stress in pullets (Sinkalu and Ayo 2008), and directly exert adverse effects on the health and welfare of birds (Minka and Ayo 2013; Sinkalu et al 2015a)
The result showed that the tdb values obtained during the study period were predominantly outside the thermoneutral zone of 18–24°C (Dei and Bumbie 2011) for mature broiler chickens, reared in a hot tropical climate
The tcloacal was measured for 3 days only, 1 week apart, in order to reduce the adverse effects of stress due to handling on the birds, known to increase the body temperature (Edgar et al 2013)
Summary
The thermal environmental conditions during the hot-dry season in the Northern Guinea Savannah zone of Nigeria, which prevails from March to May (Dzenda et al 2011) induce heat stress in pullets (Sinkalu and Ayo 2008), and directly exert adverse effects on the health and welfare of birds (Minka and Ayo 2013; Sinkalu et al 2015a). Exposure to heat stress affects the circadian rhythms of many physiological variables in livestock, which may disorganize the circadian system, and the productivity, welfare, and health status of animals (Ayo et al 1998; Piccione et al 2013; Minka and Ayo 2016b). The thermoneutral zone for poultry is 18–24°C in the tropics (Dei and Bumbie 2011), but the upper limit of this range is often exceeded in the tropics.
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