There exist a handful of signs and indicators -- some more scientific than others -- that let a hog owner know a sow has become impregnated. It's important for pig keepers to understand how to recognize a pregnant sow, from observing physical and behavioral changes to seeking veterinary confirmation. Correctly identifying a pregnant sow helps you determine the farrowing date.
Mind the Calendar
A key consideration in keeping hogs is scheduling. Pigs become pregnant easily, with a success rate of between 75 percent and 90 percent. Gilts can first become pregnant between 6 and 8 months of age. A pig may exhibit physical signs of pregnancy as early as a few weeks into gestation, corresponding with a cessation of estrus cycles -- she won't go into standing heat after 21 days. If you know the date of mating, you can plan on a farrowing date roughly 114 days later.
Experienced keepers will notice a handful of physical changes in a bred sow. The first, observable after a few weeks, is a directional change in the clitoris: When a sow is pregnant, the organ will change from a downward orientation to upward, as internal organs increase in size, pulling the reproductive system downward in the belly and causing the clitoris – the terminal point of the system – to tip upward against the increased weight. For the first 100 days, weight gain is the only other sign of pregnancy. Later changes include a swollen, often asymmetrical belly and noticeable swelling of the teats.
By late pregnancy, you've hopefully detected pregnancy through observation of physical indicators or via veterinary services, In the final weeks of a sow's gestation, she'll begin to exhibit behavioral changes exclusive to a pregnant pig nearing farrowing. A sow will begin to nest when she's within a day to three days of delivering her litter, at which point you will likely see her gathering straw or other dry materials with her mouth and building a circular nest in the area where she intends to farrow. Restlessness begins during this period -- the sow will become increasingly unwilling to lie down for long periods of time.
Don't Mistake Illness for Breeding Success
It's important to note that certain swine illnesses can mimic pregnancy symptoms. Most notably, you cannot base pregnancy determinations solely on the presence of a swollen belly, as abdominal swelling can be an indicator of problems within a pig. Among the more serious conditions that bloated belly can indicate are porcine enteropathy, lymphosarcoma and intestinal torsion. Changes in clitoris, too, can be misleading, as cervical or rectal prolapse can cause changes in the organ. New pig owners, especially, should be willing to call a vet if in doubt of sow pregnancy.