Female pigs exhibit certain physical and behavioral actions during labor, and it's good to know them, since many hog births benefit from human intervention. Well before labor begins, you'll see changes that indicate it's coming, so you'll have plenty of time to prepare.
Mind the Timeline
A key consideration when observing sows for signs of labor is knowing when insemination occurred. Pig gestation periods are easy to remember: The normal timeline from conception to birth is 112 days: three months, three weeks and three days. This timeline charts easily when artificial insemination is employed, while successful breeding between a sow and boar can be less exact. When sow impregnation is considered successful, a farmer can mark the calendar on the expected date to watch a sow for labor.
Prior to farrowing, a pig's teats appear as two lines of nipples stretched tightly along her belly, but they change starting two days prior to delivery, becoming taut. The hog's teats will "bag up" -- swell with milk 12 to 24 hours before delivery -- dropping low and close to the ground. When labor begins, the udder and teats swell to engorgement, ready for piglets to rush for sustenance. Milk, grayish at first then whitening, leaks from the teats during labor and is easily hand-expressed.
Changes in Behavior
Monitor a pregnant sow's behavior closely as delivery date approaches. Prior to labor, sows are restless. They pace and build nests with straw or available materials. Cessation of this agitated behavior indicates labor has begun. When laboring, sows lay down in the nesting area and become quiet. Abdominal straining is observable as the sow brings her legs closer to her belly; she will shiver, remaining in the straining position, until the first piglet is born.
Physical Signs of Labor
Following the quieting, straining and shivering stage of labor, but immediately prior to farrowing the first piglet, the sow passes fluid from her swollen, reddened vulva, the external organ of the female pig's reproductive tract. This blood-tinged fluid contains the small, dark pellets of her piglets' defecation, known as meconium. This part of labor indicates the final stage will begin in 15 to 20 minutes, when the first piglet is farrowed. The full litter will farrow in subsequent hours; labor ceases when the sow passes her afterbirth.