Intestinal fermentation: dietary and microbial interactions

The chapter presents a discussion on intestinal fermentation, including dietary and microbial interactions. The major benefits derived from the use of antibiotics in subtherapeutic doses in animal feeding involve: disease prevention, improved feed efficiency and increased performances, especially for the young stressed animals and where management and hygiene conditions are not excellent. In pig farming, feeding antibiotics is widely practiced around weaning, the time that represents the most challenging period a pig encounters during its life in terms of infection and abundance of stressors. Although the mechanism by which antibiotics promote growth is still under heated debate, the most reliable hypothesis relates to changes in the composition of the intestinal microflora. Some antibiotic-resistant strains of Escherichia coli have evolved compensatory mutations that preclude reversion to the sensitive state, even without selective pressure. At birth, the intestinal tract of pigs is sterile and represents a good niche for rapid proliferation of environmental bacteria. Lactobacilli, streptococci, coliforms and clostridia are the main bacterial groups that can be isolated from gastric content within the first 2–3 hours of life. Along with glucose, other metabolic fuels for the small intestine are represented by the natural polyamines: putrescine, spermidine and spermine. Another category of molecules that can play a role as microbial modulators are the prebiotics, defined as “nondigestible food ingredients” that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon.