The gastrointestinal microbiota and its role in monogastric nutrition and health with an emphasis on pigs: Current understanding, possible modulations, and new technologies for ecological studies

The gastrointestinal microbiota is an incompletely defined, dynamic community of several hundred species of primarily anaerobic bacteria. Species composition and bacterial numbers vary depending on animal age, the gastrointestinal location and a variety of nutritional and environmental factors. The microbiota positively and negatively impacts host physiology and performance in many important ways. This review will examine the establishment and composition of the normal microbiota; its beneficial and deleterious effects on the host; and methods by which to modify the microbiota. In addition, recent advances in methodology using the techniques of molecular biology to measure and describe the microbiota are discussed. Finally, recent results using the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technique to examine the microbiota of pigs at different ages, different intestinal sites, and after treatment with selected feed additives will be described.