A female pig, called a sow, can become pregnant once it is 8 months old, and usually remain fertile until they are 18 months old. Male pigs, or boars, become sexually active once they are 8 to 10 months old. During their productive months sows enter into a phase called estrus, or "heat," every 21 days when they are not pregnant, sending signals to the boar that they are ready and able to mate. Once the sow gets pregnant, the gestation period lasts 115 days.
Methods of Conception
Pig farmers generally choose to have their sows artificially inseminated. This allows farmers to breed multiple sows in the time it would take for one boar and sow to mate naturally. A normal breeding session will usually take 15 minutes, with the boar being able to mate with up to 3 sows a day. Through artificial insemination, however, a boar's semen can be used to inseminate up to 50 sows. During artificial insemination, a boar will mate with a fake sow that the farmer creates. The farmer will place the sow's penis in a jar or bottle in order to collect the semen.
Because piglets have a harder time surviving in extreme heat or cold, most modern-day pig farmers have allowed their pigs to farrow--give birth--indoors. The birthing quarters typically contain a crate that can be monitored frequently, ensuring that the piglets are being cared for properly by their mother. Most pigs who farrow indoors produce approximately 10 piglets per liter. They can reproduce twice a year.