Abstract
Long-term assessments of bio-thermal responses in a hair coat sheep breed were performed to investigate the effect of the thermal environment on their physiological performance and thermal balance. Twelve healthy non-lactating Morada Nova ewes (3 ± 1.2 years old, body mass 32.7 ± 3.7 kg) were assigned in two 12 × 12 latin square designs (from 07:00 to 19:00 h and from 19:00 to 07:00 h, respectively) for assessments of their bio-thermal responses during 24 consecutive days. There was a monophasic pattern in the ambient temperature (TA), which ranged between 21 and 38 °C, thereby exposing the ewes to different levels of surrounding TA over the day and influencing several of their bio-thermal responses (P = 0.0001). Their body temperatures (i.e., rectal, skin, and hair coat surface temperatures) gradually increased (P = 0.0001) from 04:00 h. The mean peak for rectal temperature (39.3 °C) was recorded at 19:00 h, while for skin and hair coat surface temperatures it occurred at 13:00 and 14:00 h, respectively. The sensible heat loss by long wave radiation and surface convection exceeded the metabolism of ewes when the TA was below 24 °C, which usually occurred between 24:00 and 06:00 h. During exposure to higher ambient temperatures, the sheep increased respiratory evaporative heat loss, without panting. In conclusion, the sheep regulated rectal temperature within a relatively narrow range of 1.4 °C over 24 h, and appear to be well adapted to coping with heat. Minimum 24 h body temperature was correlated with minimum TA, indicating that heat conservation strategies are likely to be important for Morada Nova sheep in a tropical biotype at night, when rates of sensible heat loss exceed the heat generated by metabolism.
•The ambient temperature ranged between 21 and 38 °C, thereby exposing ewes to different levels of surrounding air temperature.•The sheep increased respiratory evaporative heat loss, without panting.•The sensible heat loss exceeded the metabolism of ewes when the TA was below to 24 °C.•The Morada Nova sheep could have some difficulties in conserving their body heat nocturnally.