Physiological variables and estimates of heat exchange in sheep kept at thermoneutral and thermal stress temperatures

The objective of the research was to quantify the levels of heat stress, physiological variables and losses of sensible and latent heat in sheep native to the Brazilian semi-arid region, kept in a climatic chamber at thermoneutral temperatures and heat stress. The experimental design was completely randomized with five temperatures and 24 sheep, with an average age of 5.0±1.0 months and an average weight of 15.0±2.3 kg. According to the heat stress index (HSI) at temperatures from 20.0 to 28.0 °C the environment was classified as comfortable, at a temperature of 32.0 °C, the environment was classified as mild to moderate discomfort, and at a temperature of 36.0 °C, it was classified as alert. With the increase in temperature, the animals significantly (P<0.05) increased rectal and superficial temperatures and respiratory rate and, in TNT, sensitive heat exchanges corresponded to an average of 55.9 % and in HST to 12.9 % of the total, and at a temperature of 32.0 °C, sensible heat exchanges corresponded to 17.9 % and latent heat exchanges corresponded to 82.1 % and, at a temperature of 36.0 °C, 95.8 % of heat exchanges were due to latent means, of which 85.1 % were cutaneous. Sheep kept in stressful thermal conditions increase their physiological variables and eliminate the majority of excess metabolic heat through latent means (skin and respiratory tract).