Effect of Heat Stress on Lactating and Non-Lactating Blackbelly Ewes under Tropical Conditions during Summer

Currently, climate change and greenhouse emissions are a phenomenon that threatens the production of foods of animal origin and food security. This has been observed in agroecological regions where heat stress did not exist and, in regions where temperatures and relative humidity were high, it is intensifying. Hair sheep show resistance to heat stress (HS) in different warm latitudes; however, lactating ewes, due to metabolic work, produce a greater amount of heat and have more problems dissipating heat than those ewes that do not lactate. To counteract the effects caused by HS, ewes adjust their physiological parameters to avoid productive and reproductive problems that affect their production and well-being. Two groups of ewes (10 lactating and 10 non-lactating) were used to evaluate the effect of heat stress during summer under tropical conditions. In this study, a temperature and humidity index (THI) was found that ranged between 65 and 79 (morning and afternoon). Likewise, a heat tolerance coefficient (HTC) of 6 units was observed. The highest breathing frequency (BF; 115.46 +/- 35.25 breaths per minute (bpm)) and rectal temperature (RT; 38.95 +/- 0.51 degrees C) were found during the afternoon in the group of lactating ewes. The means were compared by group, time of the day, and interaction, and only significant differences were found between groups for RT and udder temperature (p < 0.001). In the case of time of day, all parameters were higher during the afternoon, regardless of the group of ewes (p < 0.001). Likewise, an interaction was found in the parameters RT, right paralumbar fossa (RPF), rump, leg, and udder (p < 0.001). In conclusion, Blackbelly ewes lactating during the summer in the tropics have higher skin temperatures, and also raise BF and RT to tolerate HS in tropical climates.