Lewis, G.S., U.S. Department of Agriculture, Agricultural Research Service, Reproduction Laboratory, Building 200, Beltsville, MD 20705, United States
Aizinbud, E., Agricultural Research Organization, The Volcani Center, Institute of Animal Sciences, Bet Dagan 50-250, Israel
Lehrer, A.R., Agricultural Research Organization, The Volcani Center, Institute of Animal Sciences, Bet Dagan 50-250, Israel

This study was conducted to determine the effects of cyclical and prostaglandin F2α (PGF2α)-induced changes in concentrations of progesterone and estrogen on changes in electrical resistance (Ω) of vulvar tissue. Also, the effects of stage of the ovarian cycle or day after PGF2α on changes in hydration of vulvar tissue were determined. Bipolar electrodes were implanted in vulvar labia of 12 Holstein cows. During 51 spontaneous ovarian cycles and after ten PGF2α-induced luteolyses, Ω of vulvar tissue was measured at least 5 days per week. Progesterone and estrogen were quantified in jugular plasma collected each day Ω was measured. To determine if Ω measured on a given day deviated from the average of Ω for the previous 4 days, a Z-statistic was calculated for each measure of Ω. In spontaneous ovarian cycles and after PGF2α, 3 to 4 days of low progesterone (< 1 ng/ml) and 1 to 2 days of increasing estrogen preceded lowest Z-statistics and maximal fluid volume in vulvar tissue. Resistance spectra indicated that total volume of fluid in vulvar tissue was greater on the day of the lowest Z-statistic during the nonluteal than during the mid-luteal phase of spontaneous ovarian cycles and was at a maximum 5 days after PGF2α. This study indicated that changes in Ω and hydration of vulvar tissue reflected cyclical and PGF2α-induced changes in progesterone and estrogen. Measuring Ω of vulvar tissue should prove useful for studying the effects of ovarian steroids on hydration of reproductive tissues and for improving reproductive management of dairy cows. © 1989.