Traditionally, hogs are kept in outdoor pens and are fed garbage and leftovers. On most modern pig farms, however, they live indoors and are fed a scientifically formulated diet. In a farrow-to-finish operation, the hogs are housed in four units—a unit for pregnant sows, a unit where sows give birth, a nursery, and a growing-finishing unit. All the units have slatted floors for sanitary purposes. In a feeder-pig operation, the farmer raises only piglets and sells them to finishing farms where they are raised to market weight.

Hogs are fed a diet composed mainly of corn and cereal grains. It is supplemented with wheat, corn bran, blood meal, meat meal, and bone meal. Pregnant sows are fed a diet of alfalfa meal supplemented with vitamins and minerals.

Among the qualities that hog breeders value and develop in their stock are early maturity; ability to bear large numbers of young; symmetry of build; and good flavor and heavy yield of lean meat.

A gilt is first bred when about eight months old. After 16 to 17 weeks a litter of 9 or 10 pigs is born. Older sows have 10 to 12 pigs in a litter, and sometimes bear two litters a year. The pigs are weaned when four to six weeks old, and are marketed when they have reached a weight of 200 to 220 pounds (90 to 100 kg), at five or six months of age.

Hogs are susceptible to several infectious diseases. Modern farms maintain rigid schedules for vaccinating the animals as well as spraying them to kill parasites. Bang's disease, or brucellosis, is a bacterial disease that causes sterility. Hog cholera is the most destructive of the many diseases that can afflict the hog. Porcine stress syndrome, a condition that occurs in hogs that have been handled or moved after having been kept in confinement, is often fatal. Death can also occur as a result of deficiencies of selenium and vitamin E in the diet. Trichinosis, a disease caused by a parasite, can be contracted by human beings who eat infected pork. .)