41 DETERMINATION OF THE RELATIONSHIP BETWEEN VULVAR SKIN TEMPERATURES AND TIME OF OVULATION IN SWINE USING DIGITAL INFRARED THERMOGRAPHY

Abstract

Accurate estrus detection is an essential component of a successful AI program in modern swine operations. It is necessary to establish efficacious means of estrus detection and optimize reproductive performance in the herd. Measurement of 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 (VST) and ovulation has not been previously investigated. Therefore, the objective of this study was to assess changes in VST that occur during the periovulatory period using digital infrared thermography (IRT). The experiment group consisted of a total of 25 gilts and 27 multiparous sows, and the control group consisted of 30 sows that were 60 days of gestation. All Yorkshire-Landrace females were housed individually in a temperature and humidity controlled environment. VST were measured twice daily at 8-h intervals using the infrared digital thermocamera (Fluke IR FlexCam^® Thermal Imager, Fluke Corporation, Everett, WA) while the animals were standing and eating prior to estrus detection. Estrus detection was performed twice daily (at 8-h intervals) with the aid of an adult boar. Once standing estrus was observed, transrectal real-time ultrasound was performed twice daily at 8-h intervals to monitor follicle development and determine the time of ovulation. Ovaries were visualized using an Aloka 500 V 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 VST and hours were reported in mean ± SEM and compared using an ANOVA and Student’s t-test using SAS software (SAS Institute Inc., Cary, NC, USA). Additionally, pairwise comparisons were performed to compare VST at different times during estrus. Significant differences were reported at P ≤ 0.05. Evidence of CL formation and ovulation was detected at 38 ± 9.3 h after onset of estrus in gilts, and 43 ± 12 h in sows. The mean VST of sows during estrus was significantly higher (P ≤ 0.05) than that of gilts. During estrus, the mean VST of gilts reached a peak of 35.6 ± 0.24°C and then decreased significantly to 33.9 ± 0.32°C 12 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 mean VST of 36.1 ± 0.25°C at 24 h prior to ovulation and then dropping to 34.6 ± 0.31°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 VST of sows and gilts measured by IRT change significantly during the periovulatory period. Additionally, there are distinct times that VST rises and then falls precipitously in sows compared with gilts. Digital IRT 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.