The relationship between electrical resistance of vaginal mucus and plasma hormonal parameters during periestrus in sows

Abstract

Sixteen crossbred multiparous sows displaying estrus on Day 5 or 6 after weaning were used in this study. Jugular veins of sows were cannulated on Day 13 of the estrous cycle. Electrical resistance of the vaginal mucosa was measured twice daily on Days 17 to 19 of the cycle and at 4-h intervals (excluding 3 a.m.) during the periestrous period. Blood 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 electrical resistance (VER) decreased 4 d before the LH peak, remained low for 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 increase 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 interval 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 (<1 ng/ml) and increasing concentrations of E 2. Profiles of E 2 and both androgens (A 4 and T) were similar; these hormones increased gradually during the follicular phase of the cycle. The highest values of E 2, A 4 and T were observed before and during the first hours of the preovulatory LH surge. Sows with ovarian cysts (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 sows. Moreover, the monitoring of VER changes provides a more reliable indication of the LH surge than detection of estrus.