There are four steps to modern pork production: breeding-gestation, farrowing, nursery and grow-finishing. After the fourth stage, pigs are ready for market.
At the breeding-gestation step, boars are rotated around sows in their estrous period. This begins around 3-5 days after their young have been weaned, then again 21 days later. Generally, farmers breed sows in the first estrous period after weaning to maximize production and sows that are not bred during this time are often sent to market and replaced. Gestation lasts for between 113 and 116 days.
When ready to give birth, sows are transferred to a farrowing room, which is a temperature-controlled pen or crate that restricts the sow's movement during and after the birth of the piglets. The piglets' sharp teeth are clipped and the tail shortened.
After they are weaned from their mother, young pigs are transferred to a nursery, another temperature controlled environment with plastic covered floors. Here, pigs have about 3 square feet each in which to move as well as access to food and water. As the pigs grow, the temperature is gradually reduced from 85 F to 70 F.
After 6-10 weeks, pigs are transferred to the grow-finishing building. They are fed continuously to reach market weight, which is between 250 and 275 lbs., and are typically sent to market at between 5 and 6 months of age.