Thermoregulatory responses, and acid–base and electrolytic balance of indigenous ewes of different coat colour in an equatorial semi-arid region

Abstract

Context Animal husbandry in thermally stressful environments can be both complex and difficult, and the anticipated effects of climate change are expected to increase this condition. Aim Thermoregulatory responses, and acid–base and electrolytic balance were evaluated in indigenous ewes of different coat colour during different moments of natural heat stress. Methods Fifteen ewes of different colour (white, red and black; five of each) were used and data were collected for six consecutive weeks in the dry and rainy periods at three times of the day [(Moment 1) 0500 hours to 0600 hours; (Moment 2) 1200 hours to 1300 hours; and (Moment 3) 1700 hours to 1800 hours)]. Thermoregulatory (clinical measures), acid–base and electrolytic variables (blood examinations) were recorded. Air temperature and relative humidity were measured, and the radiant heat load was calculated. Key results Black ewes showed higher averages of respiratory rate (RR) and rectal temperature (RT). RT was different between before and after heat stress for all ewes, while the RR was not affected and cutaneous evaporation presented minor variations. Between 1200 hours and 1300 hours, there was an increase in the hydrogen potential, oxygen pressure, oxygen saturation and total carbon concentration averages, and a decrease in partial pressure of carbon dioxide for all ewes. The base excess was not significantly different for each time of the day between the periods, and were not affected by the time of the day or the season. White ewes were highly affected by the time of the day and the period regarding electrolytic parameters, followed by the red ewes and black ewes. The first two discriminant functions showed that ewes, regardless of coat colour, show similarity in the animal responses at Moments 1 and 3, compared with Moment 2. RT was the main variable that distinguished the three genetic groups. Conclusions Indigenous ewes of different coat colour recover physiological equilibrium after heat challenges. These adjustments enable them to maintain thermoregulatory responses, and acid–base and electrolytic balance within the physiological equilibrium. Implications These variations indicated the ability of Brazilian indigenous ewes of different coat colour to recover thermoregulatory, and acid–base and electrolytic balance after an environmentally challenging condition in an equatorial semi-arid region, regardless of the period.