The role of gut microbiota in the health and disease of pigs

The pig intestine is home to a dynamic microbial population that forms a complex ecosystem and has a symbiotic relationship with the host. The population of gut microbes, or microbiota, plays key roles in maintaining nutritional, physiological, and immunological functions of the pig (Lee and Mazmanian, 2010; Brestoff and Artis, 2013). However, this microbial population also includes disease-causing organisms such as Escherichia coli, Salmonella, and Clostridia. These pathogenic organisms can cause substantial morbidity and mortality; thus, prophylactic use of antibiotics has been common in livestock industries. Disturbances in the gut microbial ecosystem during the rearing of pigs can dramatically increase risk of disease. To meet production goals in the swine industry, piglets are weaned early, before a stable microbial population is established and the immune system is mature. Stress at weaning further disrupts the gut microbial ecosystem (Konstantinov et al., 2006), increasing susceptibility to bacterial post-weaning diarrhea (Lallès et al., 2004). The use of prophylactic antibiotics tends to balance these disturbances, decreasing incidence of gastrointestinal disease, particularly at weaning. Widespread use of prophylactic and growth-promoting antibiotics has increased selective pressure for anti-microbial resistant bacteria and is now a major public health concern (Dibner and Richards, 2005). Using current knowledge of the host–microbial relationship, strategies including the use of prebiotics, highly fermentable carbohydrate cereal grains, probiotics, and (or) microbial transplants may promote animal health and reduce the need for antibiotic use. However, future research must quantitatively and qualitatively define the composition and function of a ‘healthy’ pig gut microbiota to successfully implement such strategies.