Addition of olive oil by-products to ewe's diet alters rumen microbial biohydrogenation process

Introduction: In the last decade, a huge effort has been made to increase the levels of healthy fatty acids (as PUFA) in ruminant-derived food (milk and meat), to ameliorate their nutritional quality. The addition of polyphenolic compounds to animal diet alters the digestive process of ruminants, perturbing the rumen microbial community; this leads to an enrichment of bioactive fatty acid (FA) in rumen liquor and then in milk, meat and their derived products. Pomace is a by-product from the olive oil mill extraction process, and is rich in polyphenols; therefore, thanks to its antimicrobic activity, it may be possible to modify the rumen bacterial community by its addition to animal's diet. Objectives: The aim of this study was to investigate the effects of olive oil pomace (OOP) addition to ewe’s diet on rumen microbiota. We focused our attention on the modulation of microbial process linked to the lipid metabolism. Methods: Three groups of Comisana ewes were fed with an experimental diet based of chopped alfalfa hay and extruded linseed. In two groups, diet was supplemented with two different olive oil pomace produced by a bi-phasic (OOP2) or by a three-phasic (OOP3) process of oil extraction. The effects of these diets were evaluated by rumen metagenome analysis and FA profiling of ruminal liquor. Results: Addition of OOP3 revealed an increase in rumen liquor of CLA19-11ct and a pH decrease, while with OOP2 there was an increase of C18-3n3. The microbiota of the three groups of ewes showed a marked presence of Bacteroidetes (>50%) and Firmicutes (>30%). Different ratios between Firmicutes and Bacteroidetes are individual specific and not correlated with regimens or other parameters. Significant differences between the control condition and diets supplemented with OOPs were found for bacterial groups represented at <2.0% level; among them Anaerovibrio lipolityca which is a lipase-producing species. Conclusions: Addition of OOP2 or OOP3 to ewe's diet increased the presence of unsaturated FA in ruminal liquor,which may lead to a boost in the quality of meat and milk. The major represented bacterial groups in the ruminal liquor are not significantly different in the three regimens, but a reduction of a specific bacterial group, involved in lipase production, has been highlighted.