|Abstract:||Accurate estrus detection is an essential component of a successful artificial insemination program in modern swine operations. It is necessary to establish efficacious means of estrus detection and to optimize reproductive performance in the herd. Measurement of physical and physiological traits such as body temperature, vaginal electrical resistance and vulva reddening have been investigated as methods to aid in estrus detection in swine. The relationship between vulvar skin temperature and ovulation has not been previously investigated. Therefore, the objective of this study was to assess changes in vulvar skin temperatures that occur during the periovulatory period using digital infrared thermography (IRT), which has already been successfully used as a therapeutic and diagnostic tool in various fields and species in veterinary medicine. The experimental group consisted of a total of 25 gilts and 27 multiparous sows, and a control group consisted of 30 sows at 60 days of gestation. All Yorkshire-Landrace females were housed individually in a temperature and humidity controlled environment. IRT vulvar skin temperatures were measured twice daily (8 am and 4 pm) using the infrared digital thermocamera (FLUKE IR FlexCam® Thermal Imager, Fluke Corporation, Everett, WA). Estrus detection was performed twice daily with the aid of an adult boar. Once standing estrus was observed, transrectal real time ultrasound was performed twice daily (8 am and 4 pm) in order to monitor follicle development and determine the time of ovulation. Ovaries were visualized using an Aloka 500V ultrasonics machine (Aloka Inc., Tokyo, Japan) fitted with a transrectal 7.5 MHz linear transducer which was fitted into a rigid, fixed-angle PVC adapter. Average vulvar skin temperatures (VST) and hours were reported (mean ± SEM) and compared using a MANOVA and Tukey-Kramer tests using SAS. Significant differences were reported at P ≤ 0.05. Evidence of ovulation, with the disappearing of the dominant follicle was detected at approximately 38 ± 9 hours after onset of estrus in gilts, and 43 ± 12 hours in sows. Temperature was collected at the same time during all the days of the experiment. The mean VST of sows during estrus was significantly higher (p ≤ 0.05) than gilts, although collected at the same time. During estrus, the mean VST of gilts reached a peak of 35.6 ± 1.6 °C at 32 h prior to ovulation and then decreased significantly to 33.9 ± 1.7 °C 8 h prior to ovulation. This marked change in mean VST was detected between 36 and 12 h prior to ovulation. There was a similar trend in sows with a peak VST of 36.1 ±1.3 °C at 24 h prior to ovulation and then dropping to 34.6 ±1.6 °C 12 h prior to ovulation. There was no significant difference (p ≥0.05) between VST in gilts and sows at the time of ovulation. This study demonstrated that vulvar skin temperatures of sows and gilts measured by digital infrared thermography change significantly during the periovulatory period. Additionally, there are distinct times that VST rises and then falls precipitously in sows compared to gilts. The potential to use digital infrared thermography as a predictor for ovulation in swine appears to be a promising tool. Further studies involving predictor models and hormonal assays need to be performed.