The gestation period of a pig is around 114 days. During this time, the pig will undergo a few physical changes, but these don’t become noticeable until toward the end of the pregnancy. Therefore, the most reliable means of pregnancy detection, aside from a veterinary exam, is a failure to return to the estrous cycle. If the sow is not pregnant, she will return to her estrous cycle 17 to 21 days after mating. Naturally, if you are unaware of whether or not she has mated, for example, if she’s been left alone with boars while in heat, you will need to check for signs of menstruation.
The physical signs of pregnancy don’t present themselves until around 3 months of gestation. At this time, sow will have a larger than normal abdomen, giving her a pot-bellied appearance. These are the earliest physical signs, aside from failure to menstruate. During gestation, the sow’s heartbeat will deviate from its regular pattern. This will only be apparent if you’re regularly measuring her vital signs. Commercial breeders may elect to monitor their sows this closely, but it is not typically essential.
At around 3 months in she will begin to change in appearance quite dramatically. She will have swollen udders, a swollen vulva and a distinct pot belly. The altered appearance of the belly can be quite dramatic because the loss of fat on the rest of the body contrasts with the distended abdomen.
The period before delivery is called farrowing. At this stage, her behavior will alter dramatically, as birthing instincts begin to take hold. She’ll exhibit nesting behavior, characterized by gathering up straw and forming it into a nest. Ensure she has a soft place to rest, with plenty of nesting material. Restlessness is common, as is a small amount of blood discharged from the vulva, straining and possible whining or groaning. When she’s ready to deliver her litter -- typically consisting of between 8 and 12 piglets -- she’ll lie down and cease all other activity