Resumen de Vaginal impedometry for detection of optimal breeding time in bitches
Objective—To compare the efficacy of canine vaginal impedometry in identifying the preovulatory luteinizing hormone (LH) peak to that of currently used methods (serum progesterone concentration measurement, vaginal cytologic evaluation, and vaginoscopy).
Design—Prospective study.
Animals—12 sexually intact female dogs.
Procedures—12 mature postpubertal Beagle (n = 3), Beagle-cross (2), and hound-cross (7) bitches ranging from 7.5 to 27.5 kg (16.5 to 60.6 lb) were enrolled in the study. After the onset of spontaneous proestrus, determined on the basis of appearance of serosanguineous vaginal discharge, serum progesterone assays, vaginoscopy, vaginal cytologic evaluation, and vaginal impedometry were performed daily until approximately 4 days after peak LH concentration (day 0) as measured by radioimmunoassay. Vaginal impedometry was compared against serum progesterone concentration measurement, vaginal cytologic evaluation, and vaginoscopy as a method for accurately identifying the LH peak and therefore the optimal breeding time. Ten of 12 bitches were bred with subsequent assessment of embryos.
Results—Vaginal impedometry accurately predicted the preovulatory LH peak in 5 of 11 bitches. One bitch was removed from the study because data were not collected. Of the remaining 11 bitches, 6 had their LH peak on the day serum progesterone concentration first exceeded 2 ng/mL. Crenulation scores reached 1 (mean, 1.3; 95% confidence interval, 0.8 to 1.7) on day 0 as expected; however, these scores were not significantly different from those on days −1 or 1. Vaginal epithelial cell populations did not change noticeably on day 0. Nine of the 10 bitches that were bred produced viable embryos.
Conclusions and Clinical Relevance—Results suggested that daily use of vaginal impedometry in bitches was unreliable as a method for monitoring periovulatory events. All techniques evaluated (ie vaginal impedometry, serum progesterone concentration assays, vaginoscopy and vaginal cytologic evaluation) frequently produced inaccurate results when used individually. Multiple methods should be used to identify optimal breeding time in dogs.
Vaginal mucus impedance, the electrical resistance of vaginal mucus, may be closely correlated with serum concentrations of progesterone and estradiol.1–3 Opinions differ as to whether monitoring VMI by means of vaginal impedometry could provide an accurate and specific indication of the optimal time to breed in bitches1 or whether this method is only useful for identification of the stage of the estrous cycle of a bitch.2 In sheep,3 cattle,4 pigs,5 and monkeys,6 vaginal impedometry has been used to successfully determine the time of ovulation, as indicated by low electrical resistance during optimal breeding periods. However, bitches have been found to have high electrical resistance during optimal breeding periods, a difference which may be attributed to their unique serosanguineous discharge.1,2 Additionally, bitches range widely in size and a single impedometer is unlikely to reach a consistent location among all breeds, which may make measurement of VMI inconsistent and vaginal impedometry unreliable as a method for daily monitoring of periovulatory events in this species.5,7 Currently used methods of monitoring periovulatory events to identify the optimal time to breed in dogs include serum or plasma progesterone assays, vaginal cytologic evaluation, and vaginoscopy. A serum progesterone concentration > 2 ng/mL is typically accepted as an indicator of the LH surge,8–11 yet a wide range (3 to 10 ng/mL) of progesterone concentrations has been reported as indicative of ovulation.12 These concentrations can be variable among bitches, laboratories, type of assay used, and methods of specimen handling, and may depend on whether progesterone is measured in plasma or serum.8,9,12–18 Vaginal cytologic evaluation allows the exfoliated cells of the vaginal epithelium to be examined. Cell types change throughout the estrous cycle, providing an indication of the cycle stage.19 Vaginoscopy assesses the changing appearance of the vaginal mucosa throughout the estrous cycle (crenulation) and can also provide an indication of the stage of the estrous cycle.20,21 Changes in both vaginal mucosa and epithelium are influenced primarily by circulating estradiol concentrations,8,10,11,22 which can be variable within and among bitches.10,23 In sheep, progesterone concentrations primarily influence VMI, except when progesterone concentrations are low, at which point the estradiol-to-progesterone concentration ratio also influences VMI.3 If this is also true in bitches, vaginal impedometry could provide a more consistent method for monitoring periovulatory events than methods influenced primarily by estradiol, such as vaginal cytologic evaluation and vaginoscopy.
The optimal time to breed is typically 4 to 7 days after the LH surge,11 which requires precise monitoring. Both of the vaginal impedometry studies1,2 previously performed in bitches have relied on surrogate indicators of the LH surge or time of ovulation (eg, serum progesterone assays) to evaluate the efficacy of this technique for monitoring periovulatory events. Critical assessment of these monitoring methods by comparison with direct measurements of LH concentration may enable improvements in breeding management and use of assisted reproductive technologies. Therefore, the objective of the study reported here was to compare the efficacy of canine vaginal impedometry in identifying the preovulatory LH peak against that of currently used methods, including serum progesterone concentration measurement, vaginal cytologic evaluation, and vaginoscopy. We hypothesized that use of vaginal impedometry in conjunction with these other methods would be more accurate than vaginal impedometry alone.
