Peculiarities of taxonomic and functional characteristics of rumen microbiota of dairy cows suffered from ketosis

In recent years, in the livestock farms of the Russian Federation, a sharp increase in the level of milk productivity in cattle due to the introduction of high amounts of starch into the diet while reducing the proportion of non-starchy polysaccharides negatively affected many functional characteristics of the animal organism, which led, inter alia, to an increase in the prevalence of metabolic diseases. One of these disorders is ketosis which occurs in 23-80 % of highly productive cows in the post-calving period. A negative energy balance in dairy cows during lactation leads to a violation of the coordination of lipid metabolism between adipose tissue, liver, intestines and mammary glands, which leads to ketosis. The microbial community of the rumen plays a significant role in the energy homeostasis of the host, its metabolic and physiological adaptation to periods of lack of energy. In the present research, we describe the pattern of changes of microbial community structure and ongoing microbial metabolic pathways in the rumen of dairy cows with ketosis. The aim of the study was to study the influence of the incidence of ketosis in cows on the composition and metabolic potential of the rumen microbiome using NGS sequencing and quantitative PCR with reverse transcription. The proportion of ketosis in the rumen of the cow increased taxa associated with impaired energy balance, in particular, gluconeogenesis, increased synthesis of lactate, intensification of the pathogenesis process. The abundance of phylum Bacteroidetes decreased 1.2 times (at p £ 0.05). This phylum includes bacteria related to the formation of propionate and succinate, the main sources of glucose for the gluconeogenesis process and highly valuable for cows succinic and acetic acids. In the rumen of the animal with ketosis, we found an increase (p £ 0.05) in the proportion of the genera Odoribacter and Frischella among which there are pathogens, as well as the presence of the pathogenic species Bacteroides fragilis . In the cow with ketosis, non-attributable bacteria from the genus Gp15 completely disappeared from the rumen microbiota. The reconstruction and forecasting of the functional content of the metagenomic community was also carried out using a software package. A significant difference (p £ 0.001) was revealed in the expression level of the Ldh-L lactate dehydrogenase gene between animals: the expression level of genes associated with the synthesis of this enzyme in the cow with ketosis was 128±17.9 times higher than in the clinically healthy animal. Using the PICRUSt2 and MetaCyс software package, it was shown that the level of the predicted functional potential with respect to 12 metabolic pathways of the rumen microbiome was increased (p £ 0.05) in the cow with ketosis. In particular, there was an increase in the level of predicted metabolic capabilities of the microbiome associated with the implementation of heteroenzymatic lactic acid fermentation, an increase in the possibility of hexitol degradation, the synthesis of O antigens used by pathogenic forms to avoid phagocytosis and to resist the lytic effect of the complement system, etc.