Pork production can lend itself to mechanization and reduced use of high-priced labour. Self-feeders, diets composed of grains and oilseed by-products, and construction of slotted floors and outside tanks or lagoons for manure storage have become almost universal among large-scale commercial producers in developed countries. Particularly in developed countries, most pigs are raised indoors with various means of environmental control. Air-conditioned barns for excessively hot summers and heated floors and space heating or heat lamps for cold winters are widespread.

Production methods have evolved into systems divided by the stages of the pig’s life cycle: birth, weaning, growth, finishing, and market. The three common operations are farrow-to-finish, farrow-to-feeder, and feeder-to-market. Farrowing refers to a sow giving birth. The farrow-to-finish operation is the historic foundation of the pork industry and includes all phases: breeding, gestation, farrowing, lactation, weaning, and subsequently growing the pigs to market weight. Typically, these operations have been on family farms, where owners raise pigs along with a grain operation in which much of the grain is fed to the pigs, saving the owner the cost of transporting and selling the grain. Additionally, the pig manure provides an excellent source of nitrogen, phosphorus, and potassium for fertilizing cropland. Historically, farrow-to-finish has been the most profitable type of hog enterprise. Many small-farm holders have full-time jobs in a nonfarming occupation and breed hogs to supplement their income.

Many pigs are now raised in vertically integrated systems, where ownership is maintained from the production farm through the meat-processing plant to the grocery store.

Farrow-to-feeder operations have the highest labour requirements, and many producers specialize in this part of the production cycle. It includes the management of the breeding herd, gestating sows, and piglets until they reach the growing (feeder) stage. The farmer retains control of the piglets until they are sold to another entity for feeder-to-market production. There are two common sale times—at early weaning, when a piglet weighs 5 to 7 kg (11 to 15 pounds), and at the start of the growing pig stage, when it weighs 18 to 25 kg (40 to 55 pounds) at about eight weeks. Most of these pigs are sold on a long-standing contract with a person involved in the final stage of production, feeder-to-market.

Feeder-to-market production has the lowest labour and management requirements. The producer in this stage purchases the feeder pigs and raises them to market weights in about 16 weeks. This part of the cycle requires the most feed and produces the most manure; therefore, it fits well with grain producers who have a lot of grain for feed and farmland that can use the pigs’ manure as fertilizer. It is the least profitable per head, however, and two or three times as many pigs must be produced to earn as much as a farrow-to-finish producer.

Basic dietary requirements

Pigs have the same basic nutritional requirements as humans, which include water, various vitamins and minerals, protein for growth and repair, carbohydrates for energy, and fat to supply essential fatty acids that are not synthesized in adequate quantities. Water is often a forgotten nutrient because it is usually readily available. As a guide, pigs need two to three times as much water as dry feed, depending on environmental temperatures.

The fat-soluble vitamins that must be added to swine diets include vitamins A, D, E, and K. Water-soluble vitamins—in particular, the vitamin B complex—that must be added include niacin, pantothenic acid, riboflavin, and vitamin B₁₂. Biotin, folic acid, and choline are sometimes recommended in diets of young pigs and the breeding herd. Vitamin requirements are usually listed as International Units, milligrams, or micrograms per unit of feed.

Mineral needs can be divided into major minerals and trace minerals. Major minerals that need to be added to the diet include calcium, phosphorus, and common salt. Requirements for major minerals are usually listed as a percentage of the diet. Trace minerals that need to be added to pig diets include iron, zinc, copper, manganese, iodine, and selenium. Although other minerals are required for growth, they are present in adequate amounts in feedstuffs. Requirements for trace minerals are usually listed as parts per million or milligrams per kilogram.

There is sufficient fat (about 1 percent) in the grain or feed of a pig’s diet to supply all of its essential fatty acid requirements. Protein is a source of amino acids, 10 of which are deemed essential dietary requirements for pig nutrition. An additional 11 or so amino acids can be synthesized by the pig’s metabolism and, although required for muscle growth, do not need to be present in the diet.

Corn (maize) is a favourite energy or carbohydrate source for pigs, but wheat, sorghum, milo, barley, and oats also are used if the price is favourable. Wherever abundant and reasonable in price, soybean oil meal is the favoured source of protein and amino acids, and other oil meals and high-protein by-products are used in most countries.

Special dietary requirements

The nutritional requirements of pigs vary according to their age, sex, and activities. For example, a boar’s nutritional requirements are based on its weight and the number of times it has ejaculated, whether by inseminating sows or by having its semen collected for artificial insemination.

Nutrient requirements during gestation are much lower than would be expected; the major concern is that the sows do not become overweight before giving birth. Gilts should gain about 45 kg (100 pounds) during pregnancy. This weight gain includes about 14 kg (30 pounds) for offspring, another 14 kg for products of conception (increased weight of uterus and fluids), and 18 kg (40 pounds) of general weight gain. Sows, which have already produced litters, should gain 27 to 32 kg (60 to 70 pounds). A daily balanced diet of 1.8 kg (4 pounds) of feed will meet the nutritional requirements of gestating pigs in temperate environmental conditions.

After farrowing, a lactating sow’s first milk is called colostrum, which lasts about three days. During this period, a sow needs 2 to 3 kg (4.5 to 6.5 pounds) of feed per day. Colostrum is very high in nutrients and factors that provide passive immunity to nursing piglets. This passive immunity is essential for disease resistance before piglets develop their own immunity, so all newborn piglets need to nurse immediately. Sows usually nurse their litters for two to five weeks, depending on the management system. Lactating sows have high nutrient requirements and at peak production may generate as much as 6 kg (13 pounds) of milk per day for their offspring. To prevent large weight losses in the sow, they need to be fed as much feed as they can consume. This can be as much as 10 to 12 kg (22 to 26 pounds) at three or more weeks after farrowing.

Weaned pigs are usually moved to a nursery where the temperature can be kept higher than 27 °C (80 °F) until they are about four weeks old. Piglets typically stay in the nursery for six to eight weeks. Newly weaned pigs have an immature digestive system, and their first diet after weaning until about four weeks of age should contain dried milk products in addition to energy and protein sources. Typically, nursery pigs are fed two to four different diets as they grow.

Growing pigs should be fed at least four distinct diets to optimize gain. As a pig grows, it eats more each day, but the nutrient density can be reduced.