Influence of olive cake supplementation on the gut microbial communities in dairy cows

The use of agro-industrial by-products as feed supplements in animal nutrition represents a strategy to reduce feeding costs and satisfy the nutritional needs of livestock. Particularly, the use of olive by-products, such as olive cake (OC), became widespread as a feed supplement since they are rich in nutraceutical molecules with antioxidant and antimicrobial features, including polyphenols. In this context, the aim of the study was to investigate the effect of the dietary olive cake supplementation, on both composition and dynamics of the faecal microbiota of dairy cow. A total of 18 lactating cows were allocated, according to days in milking, parity, and milk yield, into 1 of 2 dietary isoenergetic and isonitrogenous treatments: control group (CTR) was fed a conventional concentrate, whereas treated group (OC) was fed a concentrate with 8% of OC integration during 28-d experimental period. Concentrates were isonitrogenous (20% of CP/kg DM) and isoenergetic (1.05 UFL/kg DM). Genomic DNA has been extracted from faecal samples and the 16S bacterial gene has been sequenced with Illumina Miseq and raw reads have been processed using QIIME2 pipeline. 10 phyla, 51 families and 78 genera were detected in the control samples whereas 10 phyla, 44 families and 78 genera were detected in treatment samples. Results showed that Bacteroidota and Firmicutes were identified as the dominant phyla, accounting for over 90% of the total bacterial population. The Desulfobacterota phylum, able to reduce sulphur compounds, was detected only in faecal samples of OC cows, whereas the Elusimicrobiota phylum, a common endosymbiont or ectosymbiont of various flagellated protists, was detected only in CTR cows. In addition, both Oscillospiraceae and Ruminococcaceae families were found only in the OC group and their growth can be associated with the presence of the polyphenols content in the diet. These two families are able to ferment complex plant carbohydrates and to produce short chain fatty acids. In conclusion, the predominance of Firmicutes and Bacteroidota, associated positively to promote the health, and the exclusive presence of Oscillospiraceae and Ruminococcaceae in the experimental group, confirm that olive cake is a valuable feed supplement for cow’s nutrition.