Vaginal impedance measurement used for mating in the rat

An apparatus consisting of 2 silver ring electrodes attached to a plastic rod and connected to a transistor indicator was used to measure electrical impedance changes in the vagina of rats. A statistically significant increase in electrical impedance occurred at proestrus. By determining when this peak occurs, the optimal time for pairing can be established. In paired animals the absence of the peak provides a reliable means of diagnosing pregnancy.