MELATONIN ENTRAINS CIRCADIAN RHYTHMICITY OF COLONIC TEMPERATURE IN LAYING HENS DURING THE HOT-DRY SEASON

Experiments were conducted with the aim of evaluating effects of melatonin on fluctuations in colonic temperature (CT) of 26 Isa Brown layers during the hot-dry season. The CT of 14 melatonin-treated and 12 control laying hens were taken for 2 days, one week apart, at 06:00 h, 14:00 h, using standard digital thermometer, inserted through the cloaca into the rectum. Unlike the control birds that were given water only, the treated layers were individually administered at 18:00 h with melatonin orally at 1.5 mg/kg daily throughout the period of the experiment. The overall mean CT in experimental (n = 14) and control (n = 12) birds were 41.0 ± 0.050C and 40.9 ± 0.040C, respectively (P < 0.05). The recorded hourly CT of the melatonin-treated group was lowest at 06:00 h (40.9 ± 0.100C) and highest at 18:00h (41.2 ± 0.050C, P < 0.05). The hours of the day had an opposite effect on CT of melatonin-treated (r = 0.4154, P < 0.01) and control (r = 0.2447, P > 0.05) layers. The relative humidity was negatively correlated with the CT in both melatonin-treated (r = -0.6495, P < 0.001) and control (r = -0.3294, P < 0.05). The results indicated that only the CT of the melatonin-treated layers showed distinct diurnal fluctuations. The findings showed that layer birds administered with melatonin had higher CT values. This indicated the entrainment of CT circadian rhythm and considerable metabolic effect of melatonin administration on the treated layers. It is concluded that melatonin administration to layers sustained homeostasis and enhanced metabolic processes during the stressful period of the hot-dry season, and, thus, may enhance their productivity in the Northern Guinea Savannah Zone of Nigeria.