The relationship between vaginal mucous impedance and serum concentrationsof estradiol and progesterone throughout the sheep estrous cycle

The objective of this experiment was to assess the relationship between ele ctrical resistance of the vaginal mucosa and serum concentrations of estrad iol (E-2) and progesterone (P-4) during the estrous cycle in ewes. Vaginal impedance was recorded daily using a 2-electrode impedometer in 10 nonproli fic Western white-faced and 7 prolific Finn ewes, during the mid-breeding s eason (October to December). Transrectal ultrasonography of ovaries was per formed once a day to confirm ovulation and monitor follicle growth (follicl es greater than or equal to 3 mm in diameter) and development of corpora lu tea(CL). Jugular blood samples were collected daily for radioimmunoassay (R IA) of estradiol and progesterone. In all ewes, a decline in vaginal impeda nce (to <40 ohms) was closely associated with the onset of behavioral estru s. In both breeds of sheep, there was no significant correlation between da ily serum concentrations of estradiol and vaginal impedance throughout the estrous cycle. Daily serum concentrations of progesterone and the E-2:P-4 r atio were correlated with vaginal impedance during the period of luteolysis and follicular phase in both breeds (Western white-faced ewes: r = 0.62, P = 0.0002 and r = -0.56, P = 0.0002; Finn ewes: r = 0.61, P = 0.001 and r = -0.45, P = 0.03, respectively) and early in the cycle (Days 0 to 2, Day 0 = day of ovulation) in white-faced ewes (r = 0.61, P = 0.0003 and r = -0.36 , P = 0.052, respectively) but not during the remaining portion of the lute al phase in either breed. In conclusion, vaginal mucous impedance appears t o be primarily controlled by progesterone, but it also changes in response to shifts in the E-2:P-4 ratio when progesterone concentrations are low. Im pedometric characteristics of the vaginal mucosa in cyclic ewes are an indi cator of serum concentrations of progesterone and E-2:P-4 ratios during the terminal stage of the estrous cycle. (C) 1999 by Elsevier Science Inc.