THE RELATIONSHIP BETWEEN ELECTRICAL-RESISTANCE OF VAGINAL MUCUS AND PLASMA HORMONAL PARAMETERS DURING PERIESTRUS IN SOWS

Sixteen crossbred multiparous sows displaying estrus on Day 5 or 6 aft er weaning were used in this study. Jugular veins of sows were cannula ted on Day 13 of the estrous cycle. Electrical resistance of the vagin al mucosa was measured twice daily on Days 17 to 19 of the cycle and a t 4-h intervals (excluding 3 a.m.) during the periestrous period. Bloo d was sampled every 4 h beginning on Day 17 and continuing for 6 to 7 d. Blood samples were assayed for LH, P-4, E(2), androstenedione (A(4) ) and testosterone (T) by radioimmunoassay. All data were standardized to maximum LH concentration (0 h). The mean LH surge lasted about 28 h and its mean amplitude was 6.5 + 0.8 ng/ml of plasma. Vaginal electr ical resistance (VER) decreased 4 d before the LH peak, remained low f or 3 d and gradually started to increase after 0 h. The first signs of estrus were observed 16.9 + 17.8 h prior to the LH peak. The range of the interval was -44 h to +8 h. The increase in VER followed peak LH by 6.2 + 4.5 h. Intervals from peak LH to the beginning of the VER inc rease ranged from 0 to 16 h. Variation of the interval from the onset of estrus to the LH peak was significantly higher than that of the int erval from LH peak to the beginning of the increase in VER (P<0.005). The decrease in the VER observed during the follicular phase coincided with low levels of P-4 (<1ng/ml) and increasing concentrations of E(2 ). Profiles of E(2) and both androgens (A(4) and T) were similar; thes e hormones increaded gradually during the follicular phase of the cycl e. The highest values of E(2), A(4) and T were observed before and dur ing the first hours of the preovulatory LH surge. Sows with ovarian cy sts (n=3) had atypical patterns of electrical resistance and aberrant plasma hormone concentrations. These results indicate that measurement of VER can be utilized for detection of LH surges during estrus in so ws. Moreover, the monitoring of VER changes provides a more reliable i ndication of the LH surge than detection of estrus.