Oestrous symptoms in primiparous sows. 2. Factors influencing the duration and intensity of external oestrous symptoms

The study comprised observations in 203 Swedish Yorkshire primiparous sows, fed a commercial Swedish feeding regime during lactation. Oestrous detection was performed twice daily after weaning until all oestrous symptoms after the first oestrus had ceased. A boar was present during the morning inspection. Blood samples for determination of plasma progesterone were drawn regularly after weaning. Only sows that showed standing oestrus and also ovulated at the first oestrus after weaning were included. atistical analyses included 189 sows with an interval from weaning to first oestrus (IWO) of 3–10 days. There was a significant positive correlation between the IWO and the duration of prooestrus and a negative correlation between the IWO and the duration of standing oestrus. The IWO did not influence the intensity of the reddening and swelling of the vulva. Body weight and backfat at weaning or the loss of weight and backfat during lactation did not influence the duration or intensity of the oestrous symptoms. Litter size at 3 and 6 weeks was negatively correlated (P < 0.05) with the total duration and the intensity of the reddening and swelling of the vulva. Litter weight gain did not influence the duration or intensity of the oestrous symptoms. In seasons with long day length (second and third) the duration of prooestrus was shorter than in the season with short but increasing day length (first). Neither the duration of standing oestrus nor the intensity of the reddening and swelling of the vulva were influenced by the seasons.