Diurnal rhythms of heart and respiratory rates in donkeys of different age groups during the cold-dry and hot-dry seasons in a tropical savannah

Abstract

The aim of this study was to determine the effect of season on diurnal rhythms of heart (HR) and respiratory rates (RespR) in the adult, yearling, and foal donkeys during the cold‐dry and hot‐dry seasons under natural light/dark cycle. The resting HR and RespR were recorded bihourly for 24 consecutive hours from 06:00 to 06:00 h (GMT +1) in 30, clinically healthy donkeys (10 adults,10 yearlings, and 10 foals). Dry‐bulb temperature (DBT), relative humidity (RH), temperature‐humidity index (THI) and wet‐bulb globe temperature index (WBGT) inside the pen were recorded bihourly from 06:00 to 06:00 h. Values of DBT, THI, and WBGT obtained during the hot‐dry season were significantly (P < 0.05) higher than corresponding values recorded during the cold‐dry season. Application of single‐cosinor procedure showed that HR and RespR exhibited daily rhythmicity in both seasons. The mesors of the HR in adult (41.51 ± 0.34 beats/min [bpm]), yearling (40.80 ± 0.43 bpm), and foal (47.55 ± 0.40 bpm) donkeys during the cold‐dry season were significantly (P < 0.01) lower, compared to the corresponding values of 48.4 ± 0.40 bpm, 50.42 ± 0.52 bpm and 58.10 ± 0.50 bpm, respectively during the hot‐dry season. The mesors of RespR in adult, yearling, and foal donkeys during the hot‐dry season were higher (P < 0.05), when compared to the corresponding values recorded in the cold‐dry season. The HR and RespR of foals were significantly (P < 0.05) higher than those of the adult and yearling donkeys. Amplitudes of HR and RespR were higher during the hot‐dry season than the cold‐dry season. In conclusion, seasonal changes affect diurnal rhythmicity of HR and RespR of adult, yearling, and foal donkeys during the cold‐dry and hot‐dry seasons. The HR and RespR of donkeys vary with age, with higher values in the foals than the adult and yearling donkeys in both seasons.

Modulatory roles of melatonin on respiratory and heart rates and their circadian rhythmicity in donkeys (Equus asinus) subjected to packing during the hot-dry season

“…The result in packing (with melatonin) donkeys was similar to the report of Zakari et al (2018b) , who reported that the peak RR occurred at 14:10 ± 0.2 h in yearling donkeys during the hot-dry season, while the acrophase obtained in packing (without melatonin) was significantly higher. This observation may be due to the effect of packing and the antioxidant effect of melatonin in the donkeys that were administered melatonin and subjected to packing.…”

“…Body temperature has direct influence on the value of RR ( Mortola, 2004 ) and melatonin has been reported to have capacity to reduce body temperature ( Cagnacci, 1996 ; Depres-Brummer et al, 1998 ; Atkinson et al, 2005 ; Simko et al, 2016 ), thereby indirectly influencing the rhythm of RR. The mesor of RR obtained in the current study was higher compared to the value obtained by Zakari et al (2018b) in donkeys that were not subjected to packing. The difference in the observations may be due to the impact of packing on the donkeys.…”

“…An increase in the cardiac output via the mechanism of increase in stroke volume may facilitate the efficiency and volume of work output in the pack donkeys, particularly if they are to be subjected to packing for long period during the thermally stressful hot-dry season. The mesor of HR (43.64 ± 1.1 beats/min) and amplitude (4.22 ± 0.8) recorded in packing (with melatonin) donkeys were lower than mesor (50.40 ± 0.52 beats/min) and amplitude (28.00 ± 1.80) reported by Zakari et al (2018b) in yearling donkeys that were not subjected to packing during the hot-dry season. The difference may be due to the antioxidant effect of melatonin.…”

Effects of packing on the diurnal rhythms of respiratory and heart rates in donkeys during the hot-dry season

“…Measurements of basic physiological parameters are easy to access and are used as the first indicators of the well-being of working donkeys. The HR of an animal is one of the physiological parameters measured to determine its health status or response to activities with increased energy demands, like packing [ 2 , 25 ]. In order to ensure more humane handling of the donkey, there is need to obtain information that will maximise their potential use in packing and be beneficial in establishing guidelines for their humane handling for packing purposes in different seasons of the year.…”

“…The RR and HR of donkeys have been reported to increase after packing exercise [ 13 , 19 ]. The daily rhythmicity of RR and HR has been reported in donkeys during the hot-dry season [ 25 ]. However, the effects of different workloads on the daily rhythmicity of RR and HR during the hot-dry season have not been investigated.…”