Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Exposure of sows to summer heat decreases reproductive performance, with a decrease in follicular development and an increase in the occurrence of anestrus (i.e., lengthening of the weaning-to-estrus interval). The present study concentrates on late gestation, farrowing/lactation and rebreeding to determine which period of the reproductive cycle is most sensitive to heat stress. Two different thermal environments were evaluated, by simulation, within the Brody Environmental Center at the University of Missouri. They included a simulated forced-air cooling (HOT) environment resulting in a condition several degrees warmer than outside air, and a simulated evaporative cooling (COOL) environment which was cooler than outside air temperature. Primiparous sows (n= 22) were moved into chambers three weeks prior to expected farrowing date and treatments begun. Exposures were HOT or COOL, in four different combinations, for gestation, farrowing/lactation and rebreeding periods. Measurements of thermal status (i.e., rectal temperature, shaved skin temperature, respiration rate) were made 4 times daily during the temperature cycle. Respiration rate and rectal temperatures were determined not to be very good indicators of heat stress, while ear skin temperatures demonstrated significant differences and, thus, would likely be a useful parameter in the development of a physiological strain index. Physiological strain index attributes are being evaluated to develop a model that combines air temperature with change in individual thermal status from thermoneutral baseline, and evaluated to determine best predictor of performance.