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The influence of weaning to oestrus interval, its interaction with parity and equine chorionic gonadotropin (eCG) on changes of vaginal impedance in sows after weaning was examined. The impedance measurements were carried out by a four-terminal method. Sows were monitored for oestrus via exposure to a sexually mature boar. The interval from weaning to oestrus was longer in primiparous than multiparous sows (p<0.01). A significant negative correlation was found between the interval from weaning to oestrus and parity. Repeated measures analysis showed that the interval from weaning to oestrus and parity and their interactions had a significant effect on the vaginal impedance in peri-oestrus. The vaginal impedance during pro-oestrus gradually decreased in all groups of sows with the weaning to oestrus interval from 4 to 8 days (p<0.05). In the subsequent period, the vaginal impedance increased and was significantly lower from 1 to 3 days after oestrus onset in sows with the weaning to oestrus interval 7-8 days than 4-6 days. Similarly, the vaginal impedance during pro-oestrus gradually decreased in all groups of sows with parity 1-5 (p<0.01). In the next period, the vaginal impedance increased and was significantly lower from 2-3 days after oestrus onset in sows of parity 1 than parity 2-5. Repeated measures analysis showed that eCG treatment had a significant effect on the vaginal impedance in peri-oestrus. Sows treated with eCG displayed the decrease and increase of vaginal impedance due to oestrus onset earlier than untreated sows. The results indicate that the weaning to oestrus interval, its interaction with parity and eCG markedly affect the vaginal impedance in sows during peri-oestrus.