Effects of lactation length and boar contact in early lactation on expression of oestrus in multiparous sows.

The ability to stimulate a fertile oestrus during early lactation provides an opportunity to increase piglet weaning age whilst maintaining 2.4 litters per sow per year. This study evaluated the effects of boar contact beginning on day 7 of lactation and lactation length on lactation oestrus induction and subsequent reproductive output in multiparous sows (parity 2.9 ± 0.16; mean ± SEM; range 2-6). Large White × Landrace multiparous sows were allocated to one of four treatment groups; weaning at 26 days post-partum and no boar contact (control); weaning at 26 days and boar contact (BC); weaning at 7 days and boar contact (BC+short lactation (SL)); and weaning at 7 days and no boar contact (SL). Control and SL sows were taken for a short walk daily during which a backpressure test was performed in the absence of a boar. Oestrus expression within 26 days of farrowing was significantly higher in BC (67%) and BC+SL (93%) sows than control (11%) and SL (13%) sows (P<0.05). Of sows mated within 26 days of farrowing, there was no difference in the number of piglets born alive or stillborn. Therefore, boar contact is an effective method to stimulate oestrus within 26 days of farrowing in both lactating and weaned sows.