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This study aimed to evaluate the effects of packing (load carrying) on the diurnal rhythms of respiratory and heart rates in donkeys during the hot-dry season. Twenty 2- to 3-years-old donkeys weighing 93 ± 2.7 kg were divided into two groups to serve as subjects: Group 1 was subjected to packing + trekking, while group 2 was subjected to trekking only. All donkeys trekked 20 km on each experimental day. The procedure was repeated three times at one-day intervals. Thermal environmental parameters were recorded. Respiratory rate (RR) and heart rate (HR) were measured before and immediately (15 min) after the packing and/or trekking period. Continuous recordings of parameters were performed for 27 hr at 3-hr intervals beginning 16 hr after the last packing and/or trekking period. The RR rose significantly (P<0.05) immediately after packing + trekking and trekking only, from 30.15 ± 0.5 and 27.52 ± 0.5 cycles/min before packing + trekking and trekking only, respectively, to 43.78 ± 3.0 and 46.30 ± 1.8 cycles/min after them, respectively. The HR (76.63 ± 4.5 beats/min) in the packing + trekking donkeys was higher (P<0.05) than that of the trekking-only donkeys (62.33 ± 2.7 beats/min). The acrophase and bathyphase of the HR in both groups were recorded during the photophase and scotophase, respectively, with higher values (P<0.05) in the packing + trekking donkeys than in the trekking-only donkeys. The circadian rhythms of RR and HR did not differ between the groups of donkeys. In conclusion, packing + trekking was more stressful to the donkeys, significantly increasing the HR of donkeys subjected to packing + trekking, compared with trekking only.

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