The sow comes into season every fifteen to seventeen days and the most outward sign of this is the sight of her trying to mount her companions. However, there is another one which experienced owners and breeders would recognise and that is P.M.T.!
There is no doubt in my mind that many of them suffer from this condition in the same way as their human sisters can. If you see a sow who is being uncharacteristically quarrelsome and feisty with her sister sows, ten to one she will be in season the following day and trying to mate anything that moves. I have also noticed that the ones who suffer the worst are those that are the most sexually active when they do come into season.
The season can last for up to forty-eight hours but the sows are only likely to be successfully impregnated during the actual oestrus which lasts from two to fifteen hours. This proper name for these hours are postpartum but I like to think of it as 'postapiggy!.'