Abstract
This study aimed to identify the temperature range at which heat stress occurs for sows in farrowing piggeries, from the perspective of barn environmental management using segmented regression analysis. The physiological responses of rectal temperature, skin temperature, and respiration rate used as dependent variables, while the independent variables were ambient temperature, the temperature–humidity index (THI), and the wet-bulb globe temperature (WBGT) were used as independent variables. The breakpoints obtained from the segmented regression analysis were 29.1 °C for ambient temperature, 79.6 for THI, and 25.4 °C for WBGT when rectal temperature was used; 17.1 °C, 61.4, and 12.4 °C, respectively, when skin temperature was used; and 22.3 °C, 70.9, and 22.1 °C, respectively, when respiration rate was used. When the respiration rate breakpoint was defined as the heat stress caution zone and the rectal temperature breakpoint as the heat stress danger zone, the caution zone for heat stress in sows in farrowing piggery was estimated to occur at ambient temperatures ≥22.3 °C, THI ≥70.9, and WBGT ≥22.1 °C, whereas the danger zone was estimated to occur at ambient temperatures ≥29.1 °C, THI ≥79.6, and WBGT ≥25.4 °C. Furthermore, WBGT, which integrates ambient temperature, relative humidity, and radiant heat, is an effective index for evaluating heat stress and guiding environmental improvements in farrowing piggery.
