Intravaginal impedance and sexual behavior of ovariectomized goats given estrogen alone or in combination with progesterone

Intravaginal impedance (IVI) fluctuates during the goat estrous cycle. To understand which ovarian steroids are responsible for IVI changes and whether IVI variations are associated with precopulatory and copulatory behaviors, 8 ovariectomized females were assigned to 4 treatments in a 4 x 4 Latin square replicated over four 8-d periods. The treatments were as follows: progesterone plus estradiol-17beta (P4 + E2), oil plus estradiol-17beta (E2), progesterone plus oil (P4), or oil (OIL). Daily IVI measurements at the vagino-cervical junction were taken at 1 and 70 KHz. Progesterone was given on d 2 and 3. Estradiol was given in the evening of d 5. On d 1 to 8, goats were group-exposed to a sexually experienced male and observed for the expression of sexual behaviors. On d 6 and 7, IVI was less when goats received P4 + E2 or E2 compared with goats given P4 or OIL (P < 0.05). Impedance measured at 1 kHz tended to remain lower on d 8 in P4 + E2-treated females compared with those given P4 or OIL (P < 0.055). Like previous results, P4 + E2 or E2 treatment induced behavioral estrus; 5 of 8 P4 + E2-treated and 5 of 8 E2-treated females were sexually receptive on d 6. On d 7, although IVI remained low and 2 of 8 P4 + E2-treated goats and 4 of 8 E2-treated goats remained sexually receptive, no additional females were in estrus. No IVI decreases and no estrous behavior were observed in goats given P4 or OIL. This experiment demonstrated that E2 initiates the periestrous drop in IVI, and P4 may delay baseline return.