Reproductive performance and oestrous symptoms in primiparous sows

The reproductive performance of primiparous sows is of great concern to pig fanners. A high percentage of the sows are culled after the first weaning due to reproductive failures. Primiparous sows often lose more weight during lactation and have a longer interval from weaning to oestrus (IWO) than older sows. The present studies were performed to provide more information about factors influencing 1) the ability to return to oestrus within 10 days ofweaning, and 2) the variation in weight loss during lactation in primiparous sows kept under the same feeding regime. The oestrous symptoms were studied. Weight and backfat were checked at farrowing and at weaning and plasma progesterone was determined regularly after weaning confirming ovulation. All sows were of Swedish Yorkshire breed and were kept under the same restricted feeding regime, based on litter size, during the six weeks oflactation.Large weight loss and to some extent large backfat loss during lactation and large litter weight gain had an unfavourable influence on the IWO. High age at pubrty was unfavourably correlated to the IWO. Short but increasing day length and a short time of boar stimulation daily after weaning had a favourable influence on the IWO.Sows with large weight loss during lactation had a higher total disease incidence during lactation and seemed to be in a more catabolic state during late lactation than sows with small weight loss.Daily boar stimulation after weaning and good ability to show standing reflex at puberty were both favourable for the ability to show standing reflex at the first ovulation after weaning. An increasing interval from weaning to oestrus prolonged the pro-oestrus and shortened the standing oestrus. During the season with short but increasing day length the pro-oestrus was longer than during seasons with long day length. Pigs with high intensity and long duration of the vulvar symptoms at puberty were also more likely to have strong and long vulvar symptoms after weaning than pigs with weak and short vulvar symptoms at puberty