Effect of sow parity on vaginal electrical impedance

The influence of sow parity on the changes of vaginal impedance after weaning was examined. Sows were monitored twice a day for oestrus via exposure to a sexually mature boar. The criterion for confirmation of ovulation was an increase in plasma progesterone levels above 12.5 nmol l−1 8 and 12 days after oestrus onset. The impedance measurements were carried out by a four-terminal method. In sows of all parities, the vaginal impedance decreased gradually after weaning (P<0.01) and increased during oestrus (P<0.01). No significant impedance changes were observed thereafter. The vaginal impedance was higher in sows above 6 parities than in sows from parities 1 to 5 from the beginning of oestrus to 14 days after oestrus onset. The impedance was also higher in sows of parity 6 than in sows of parity 1 from the beginning of oestrus to 14 days after oestrus onset and in sows from parities 2 to 5 than in sows of parity 1 from 2 to 4 days after oestrus onset. The difference in average impedance values between sows above 6 parities and sows of parity 1 was two-fold in oestrus compared to the luteal phase. In all measured places of the vagina from the cervix to 6 cm from the cervix, a similar significant increase of impedance was observed during oestrus. The results indicate that the parity of sows affects the electrical impedance of vaginal mucosa measured by means of a four-terminal method.