Acid-basic equilibrium associated to evaporative thermolysis in Brazilian locally adapted ewes

The research was led up at the N?cleo de Estudos e Pesquisa em Pequenos Ruminantes, located at Universidade Federal Rural do Semi?rido, in Mossor?-RN, aiming to evaluate the thermoregulatory aspects and its influence on the acid-basic equilibrium in the red, white and black Morada Nova sheep. The data were registered in six days during the dry period of the year, in which were evaluated the responses of the animal exposition to environmental heat conditions from 05h00min AM to 06h00min AM, from 12h00min AM to 01h:00min PM, and from 5h00min PM to 6h:00min PM. The following thermoregulatory variables were evaluated: respiratory rate, rectal temperature, body surface temperature and cutaneous evaporation on the neck and flanck region, and also blood gas tests, which determined the blood pH, venous PCO₂, and concentration of bicarbonate ions (HCO₃^-). Environmental data, such as air temperature (AT), relative humidity (RH), wind speed (W) and black globe temperature, which were used to determinate the Black Globe Humidity Index (BGHT) and the radiant heat load (RHL) data were registered, in each time of samplings. The respiratory thermolysis appeared as a mechanism more intensively used by the animals in comparison to the evaporative thermolysis, to achieve heat excess dissipation. However it can cause changes in acid basis equilibrium, in cases of hyperventilation that normally can lead to respiratory alkalosis. These disturb was verified on the red and black varieties. The most stressful period for the animals was from 12h00min AM to 01h00 PM in every six days of data collection, because of the heat stress peak, the animals activated in a more efficient way the physiological responses. The using of respiratory thermolysis appeared as the primary physiologic mechanism used to maintain the homeothermy, but the acid-basic equilibrium was altered. There was a high influence of variety and it was also observed that in spite of the positive interactions, the day of data collection had less interference on the responses.