Rumen microbiota alterations during subclinical ketosis is associated with the development of subclinical mastitis in dairy cows

Abstract Background: Mastitis is the most serious disease endangering animal husbandry, especially dairy farming. Clinical investigations indicated that cows suffering from ketosis have a higher probability of mastitis. The composition of rumen microbiota is closely related to ruminant health. However, it is not clear what role it plays in this process. Results: Blood β-hydroxybutyrate (BHBA), blood non-esterified fatty acids (NEFA), milk somatic cell counts (SCC), milk fat, fat to protein ratio, and milk urea nitrogen (MUN) were significantly elevated in all cows with subclinical ketosis (SCK)，while the milk lactose was significantly decreased. The production and proportion of volatile fatty acids (VFA) in rumen changed during SCK, with significant decreases in acetate, propionate, butyrate, and total VFA (TVFA), and a significant increase in the acetate to propionate ratio. The microbiota in rumen fluid and milk were determined by 16S rRNA gene sequencing. The results showed that the richness of rumen microflora was significantly decreased during SCK. The rumen harbored unique bacterial community in cows suffering SCK, which were significantly correlated with BHBA in plasma, SCC in milk and milk components. LEfSe analysis revealed that it was characterized by the increase of Bacteroidota , Christensenellaceae_R-7_group , Luteimonas and Thermomonas and the decrease of Prevotella . The richness of milk microflora was significantly increased during SCK. LEfSe analysis suggested a significant increase in Staphylococcus and a significant decrease in Coxiella , Acinetobacter , Oscillospiraceae_UCG-005 and Corynebacterium . Conclusions: The SCC of cows with subclinical ketosis was significantly elevated and all individuals suffered from subclinical mastitis. The rumen microbiota during subclinical ketosis changed significantly, characterized by decreased richness, increased acetate and butyrate producing bacteria and decreased propionate producing bacteria, and was closely related to blood BHBA and milk SCC. This provides a new perspective for the study of the relationship between subclinical ketosis and subclinical mastitis as well as the prevention and treatment of the two diseases.