Study on the relationships of intravaginal electrical impedance and plasma level of progesterone and estradiol-17b in estrus synchronized sows in prediction of the optimal insemination time in pig

An experiment aimed at determining the association of impedance values with plasma level of progesterone and estradiol-17b in estrus synchronized sows for prediction of optimal insemination time was conducted in Large Animal Clinic for Theriogenology and Ambulatory Service of Faculty of Veterinary Medicine, Leipzig University, Germany. Measurements of intravaginal electrical impedance (IEI) were carried out through out the estrous cycle (synchronization phase and estrus period) using a 2-electrode impedance-measuring instrument (INOTEC FEG GmbH, Germany). Values of impedance measurements were analyzed based on clinical findings including ultrasongraphy, and endocrine parameters (plasma concentration of progesterone and estradiol-17b). Blood samples were collected parallel with measuring of IEI in order to determine plasma progesterone and estradiol-17b concentrations using radioimmunoassay (RIA). High values of impedance were measured during synchronization phases/diestrus period, and low IEI values coincided with the pre-ovulatory estradiol-17b peak, at the height of standing heat. IEI values began to decline, right after withdrawal of Regumate administration, about 2 to 3 days before the onset of standing heat. Average low values of impedance were registered within 36 to 52 hours at times of standing heat. Relationship among plasma levels of estradiol-17b and progesterone and values of IEI during estrus period was evident: Low IEI values were significantly correlated to maximum plasma levels of estradiol-17b (r = 0.-24) (P < 0.05). Plasma progesterone levels also revealed significant association with IEI values (r = 0. 62) (P < 0.01). IEI values were also associated with psychosexual behavioral changes and changes in the reproductive tract during estrus period: congestion and edema of the vulva and vagina began at time of declining values of impedance, during the onset of pre-estrus phase. The average duration of ovulation was 4.1 ± 1.23 hours. This study revealed that based on values of IEI and its indirect association with estradiol-17b, the onset of estrus can be better recognized, and thus, the optimal insemination time can be predicted.