Nutrition and immunology of swine

In modern, high-density production systems, swine live surrounded by pathogenic microorganisms - bacteria, viruses, and parasites that can cause infectious disease or pathology. Nonetheless, pigs become ill relatively infrequently because they are equipped with a highly evolved immune system that affords protection against infectious microorganisms. This protection can be costly, however, as a number of studies have established that animals reared in unsanitary environments that afford a high level of host-pathogen interaction grow more slowly and consume less feed than animals reared in more sanitary environments (Coates et al., 1963; Roura et al., 1992; Williams et al., 1997b). The view is that nutrients that might have otherwise gone to support growth are redirected to support the host’s defenses against pathogenic microorganisms.