ABSTRACT
There has been a close relationship between microbes residing in the gastrointestinal tract (GIT) and the animal host during the long course of evolution (Ley et al. 2008). Nowadays the microbiota within the GIT of mammals can be considered a metabolically active organ: culture independent studies of the human microbiota recently identifi ed a complex symbiotic environment with a wide biodiversity with more than 1,000 bacterial phylotypes representing more than 7,000 strains and with a high number of cells that can reach 1014 (Backhed et al. 2005, Murphy et al. 2009). Under normal circumstances, commensal bacteria are an essential health asset with a nutritional function and a protective infl uence on the intestinal structure and homeostasis. The intestinal microbiota promotes supply, digestion and absorption of nutrients, improves growth performance,
1 Department of Agricultural Sciences, Bologna University, Via Fanin 42, 40127 Bologna, Italy.
