A multidisciplinary study investigating the bovine milk microbiome and its association with mastitis resistance traits in Holstein Friesian and Rendena dairy cows

Highly selected dairy breeds, such as Holstein Friesians, are exposed to a high risk for disease, especially mastitis, during the transition period. In contrast, autochthonous and lower-yielding dairy cattle breeds, such as Rendena, are known to possess higher resistance to disease and resilience to intensive farming conditions, especially concerning udder health and metabolic disorders during periparturient period. A more detailed knowledge of the healthy milk microbial communities and of their interactions under physiological conditions might provide suitable information about milk quality and udder health. With the aim to characterize milk microbial diversity during the transition period and its potential associations with mastitis, we used highthroughput sequencing of the 16S rRNA gene to investigate the bovine milk microbiome in 6 Holstein Friesian and 4 Rendena cows reared in the same farm and under the same environmental and management conditions. Further, in this study we applied a multidisciplinary approach to compare innate immune response patterns, inflammometabolic parameters and milk protein profiles. Quarter milk samples and blood plasma were collected from all cows at dry-off (T1), 1 day after calving (T2), 7-10 days and 30 days after calving (T3 and T4, respectively). Quarter milk samples were analyzed for somatic cell counting, bacteriological growth, characterization of the milk microbiota by 16S deep sequencing, milk protein profiling by electrophoresis and densitometry. Moreover, for each sample inflammation markers and assessment of different innate immune-related mediators such as cathelicidin, lysozyme, CD45, IL-1beta, TNF-alpha, PTX3, IL-1R8, were measured. In parallel, blood plasma samples were assessed for the main metabolic parameters. Our results indicate that the milk microbiome of Rendena cows profoundly differs from that of Holstein Friesian cows, and harbors some diversity and taxonomic markers of mammary gland health allegedly specific to Rendena cows, only. In addition, in comparison with Rendena cows, Holstein Friesian cows showed a more severe fat mobilization and systemic inflammatory response at T2 and T3. In conclusion, in spite of the same farming conditions, several differences were observed in the two breeds providing useful hints about disease resistance in autochthonous rustic breeds.