Vaginal impedance measurement used for mating in the guinea-pig.

A method for determining the phase of the oestrous cycle by measuring the electrical impedance of the vaginal mucous membrane was examined in the guinea-pig. The apparatus consisted of silver ring electrodes attached to a plastic rod and connected to a transistor indicator. A cyclic increase in impedance was found, and significantly higher values were recorded during the phase of increase (proestrus) than at other times of the cycle. By determining this peak the right time for pairing can be chosen. Conversely, the disappearance of this cyclic culmination in impedance pointed to early pregnancy with a high degree of reliability.