In large commercial farms, swine production is even more complex, having moved beyond the traditional one-site or two-site production system. On these farms, pigs are weaned at much earlier ages, sometimes when only ten to fourteen days old. This technique, called medicated early weaning, was developed in Britain in the 1980s by veterinary medicine professor Tom Alexander at the University of Cambridge. Alexander discovered that very early weaning could prevent a sow from passing certain swine diseases to the next generation of piglets. Weaned pigs are moved to separate nursery buildings, at enough distance to lessen the chance of infection by wind-born disease agents. The pigs are usually held in the nurseryfor seven weeks. before they are moved to another set of buildings for the "finisher-production" stage, where they reach slaughter weights.
Until the late twentieth century, pigs were weaned from their sow from about thirty-five to fifty-six days after they were born. From a birth weight of about three pounds, they would reach a weaning weight of about forty to fifty pounds by fifty-six days. After a short period of receiving a rich "starter feed" of grains, milk products, and perhaps medication, the pigs were ready to sell to another farmer who specialized in "finishing," or feeding hogs to market weights. Sometimes the farmer whose sows produced the pigs would keep the pigs and move them to another barn or pen to feed them to market weight in a method of production called "farrow to finish." (Farrowing refers to the action of a sow giving birth.) Farrow-to-finish production was typical of small-and medium-size "family farms" in North America. On some farms, farrowing took place in small huts big enough for one sow, placed in a pasture of alfalfa or other digestible forage. After 1950, farrowing more commonly took place in specialized buildings or modified barns.
This multisite system of production has existed along with the more traditional ones, in which farmers raised only a few hundred or a few thousand pigs for slaughter. But at the start of the new millennium, multisite production was rapidly taking over the industry. In Corn Belt hog-producing states, individual families that ran grain farms still fed hogs, but only in the second and third stages of multisite production. The families no longer owned the pigs. Instead, they raised them for large companies, much as local entrepreneurs run franchise outlets for fast-food chains. The pigs were owned, from birth through slaughter, by large companies, including packers. The parent animals in this system are complex proprietary mixtures of breeds owned by a handful of multinational companies. By the late 1990s, more than half of U.S. production was in some stage of this "vertical integration," meaning that each step in hog raising is owned or controlled by one company. The multisite pig production system was becoming global, existing not only in the United States and Britain, but also in Canada, Mexico, Brazil, Chile, Spain, Germany, Poland, Italy, China, and France.
Exactly why so much of the pig is cured and made into bacon and ham, while less beef and lamb is consumed as dried or smoked products may be a question for archeologists, not historians. One theory about the popularity of cured pork, offered by the National Pork Board, is that pork is a mild meat that, having less flavor than some meats, readily takes on added flavors.