The activity deals with nutritional studies in small ruminants (sheep and goats), in three main areas: (i) nutritive evaluation of conventional and non-conventional feedstuffs and products quality, (ii) study of the fermentation and microbial ecology in the rumen and the interaction of the microbes with the host immune system and (iii) environmental impact of ruminants production. The study of the rumen fermentation and the microbial ecosystem currently represents the most important activity within this subline, given the key role that the rumen ecosystem plays in the nutrition of the ruminant. A wide range of in vitro techniques to study the rumen metabolism are currently used, which contributes to minimize the use of experimental animals. We are optimizing and developing new molecular tools which, combined with classical culture techniques, will contribute to better understand the interactions between microbes and of microbes with the host, especially with its immune system. In response to the increasing public concern on the environmental impact of animal production, we try to increase digestion efficiency and understanding the role of ruminal microorganisms on the fibre degradation, lipid metabolism and methane production by applying genomic technologies in order to maximize the use of lignocellulosic by-products and decrease methane and nitrogen emissions by ruminants.