Melatonin modulates behavioral and oxidative stress responses in donkeys (Equus asinus) subjected to packing during hot-dry conditions

The aim of the study was to evaluate the effects of melatonin administration on oxidative stress and behavioral responses immediately (1-h) post-packing and 16-h post-packing circadian rhythms in donkeys during hot-dry conditions. Twenty healthy pack donkeys (15 males and five non-pregnant females), aged 2–3 years with average weight of 93 ± 2.7 kg were divided into two groups randomly. Melatonin was administered at a dose of 10 mg per donkey for 7 days to group 1 donkeys (packing + melatonin) that were subjected to packing (load-carrying), group 2 (packing–melatonin) donkeys were packed only without melatonin administration. The donkeys trekked covering 20 km, three times during the one week experiment, one day apart. Meteorological parameters were recorded during the study period. Serum harvested from the blood sample collected from each donkey before and after packing was analysed for oxidative stress biomarkers. Behavioral parameters were evaluated using the focal animal sampling technique for 1 h immediately (1-h) after packing and at expiration of 16-h post-packing, covering 27-h period at 3-h intervals. Melatonin reduced oxidative stress by preventing reduction in catalase activity and total antioxidant capacity in packing + melatonin donkeys. Melatonin exerted anti-stress effects on behavioral activities in the treated donkeys post-packing by significantly reducing (P < 0.05) the percent duration of grooming, walking and standing, but significantly increasing (P < 0.05) the percent duration of feeding, compared to the control donkeys. In conclusion, melatonin exerted beneficial effects against stresses due to packing and heat, and influenced the circadian rhythms of behavioral activities. Its administration may reduce the risk of negative effects of environmental heat stress and stress due to packing in donkeys during hot-dry conditions.