Characterization of microbiome on faeces, blood and milk in dairy cows with different milk leucocyte pattern

Mastitis is an inflammatory disease of the mammary gland, caused by the invasion of microor-ganism on this site, associated to an altered immune response. Recent studies in this field hy-pothesize that the origin of these pathogens can be also from the gastrointestinal tract, through the entero-mammary pathway in relation to an increase gut permeability. In this study, we wanted to investigate if inflammatory status of the mammary gland is related to an alteration of gut per-meability. The microbiome of faeces, blood and milk of lactating cows, recruited on the basis of the total somatic cell count and of percentage of polymorphonuclear neutrophils and lymphocytes, was studied. Cows were divided in healthy (G), at risk of mastitis (Y) and with mastitis (R). The bacterial DNA was extracted and the V3 and V4 regions of 16S rRNA sequenced. Moreover, quantification of total bacteria was performed with quantitative Real-Time PCR. A non-parametric Kruskal-Wallis test was applied at the phylum, family and genera levels and beta biodiversity evaluated with the unweighted UniFrac distance metric. Significant differences between groups were found for the microbial composition of faeces (Clostridiaceae, Turicibacteriaceae for family level and Clostridium, Dorea, SMB53 and Turicibacter for genus level), blood (Tenericutes for phylum level and Mycoplasma for genus level) and milk (OD1 and Proteobacteria for phylum level, En-terobacteriaceae and Moraxallaceae for family level and Olsenella and Rhodococcus for genus level). The beta biodiversity of faeces and blood did not change between groups. Indeed, significant differences (p<0.05)were observed between the beta diversity in milk of G group and Y group and between Y group and R group. The number of taxa in common between faeces, blood and milk where 8 at a phylum, 19 at a family and 15 at a genus levels. From these results, the bacterial crossing from gut to milk in cows was not confirmed but remained hypothetical.