J. E. Pettigrew
Microbial populations in the digestive tract are influenced by many factors, but one of the most important is likely to be the supply of energy substrate present in the tract. That substrate supply is largely a function of the diet; the supply in the lower tract is largely a function of the amount and type of indigestible but fermentable carbohydrates in the diet. Different cereal grains have widely different carbohydrate components, so they should be expected to result in widely different supplies of fermentable carbohydrates in the lower gut.
A high level of fermentable fiber in the diet may have either beneficial or detrimental effects on the pig. It may promote the development of a large population of commensal bacteria, which protect the pig from entertic infection by inhibiting the growth of pathogens. Alternatively, it may serve as an energy substrate for pathogens and therefore increase susceptibility to disease. Our recent data provide general support for the latter.