Effects of melatonin on cloacal temperature and erythrocyte osmotic fragility in layer hens during the hot-dry season

Experiments were conducted with the aim of determining effects of melatonin on fluctuations in cloacal temperature (CT) and erythrocyte osmotic fragility (EOF) of layer hens. The CT of 14 melatonin-treated and 12 control laying hens were taken for 2 days, 1 week apart, at 06:00 h, 14:00 h and 18:00 h, using a standard digital thermometer inserted into the cloaca. The control birds were given water only, while the treated layers were individually administered at 18:00 h with melatonin orally. On day 12 of the administration, venous blood samples were collected from the layer hens to determine EOF. The overall mean CT values in melatonin-treated and control birds were 41.0 +/- 0.05 degrees C and 40.9 +/- 0.04 degrees C, respectively (P < 0.05). CT of the melatonin-treated group was lowest at 06:00 h (40.9 +/- 0.10 degrees C), but highest at 18:00 h (41.2 +/- 0.05 degrees C; P < 0.05). At 0.1%, EOF of 62.01 +/- 3.75% obtained in melatonin-treated layer hens was lower (P < 0.001) than the corresponding value of 73.86 +/- 2.59%, recorded in control layer hens. In conclusion, melatonin administration to layer hens sustained thermal homeostasis and decreased EOF in layer hens during the hot-dry season.