Measurement of electric resistance of the vaginal mucus as an aid for heat detection.

Abstract This is a review of a series of investigations of the electric resistance of the vaginal or cervical mucus as an indication of the optimum time for conception during the estrous cycle in cows, sheep, pigs, and bitches. For the purpose of differential diagnosis in cows, measurements were made during different stages of pregnancy and in pathologic conditions of the genital organs. A probe containing two electrodes and an Ohmmeter to measure resistance of electric current was developed. There was a distinct relationship between the resistance measurements and the stages of the estrous cycle in the cow. The lowest values were observed during estrus and coincided with the optimal time for breeding. In ovariectomized animals no changes in resistance were observed. After treatment with estrogen, resistance levels dropped to levels similar to those observed in intact animals at the time of estrus. Pathologic conditions of the genital organs, such as follicular cysts and endometritis, resulted in values corresponding to those observed during estrus. In sheep and pigs, there was a similar correlation between resistance of cervical and vaginal secretions and the estrous cycle. In contrast, very high Ohm values were observed in the bitch during estrus, probably because of the mixture of blood in the mucus. The intravaginal measurement of resistance of vaginal or cervical secretions seems to be a useful method for objectively determining estrus. The method offers opportunities for estrus determination, not only in single animals but in large populations under field conditions. The determination of the optimal time for conception in individual animals still remains difficult due to the need for repeated measurements with the presently available instrument. Telemetric approaches have been successfully tested and offer possibilities for future development of instruments which would constantly monitor resistance and transmit to a recording instrument.