Associations between hyperketonemia and the rumen metagenome and metabolome in Holstein cows during the first 2 weeks postpartum.

Hyperketonemia (HYK) is characterized by elevated levels of blood ketone bodies in dairy cows. Despite previous research on the physiological events related to HYK, associations between the rumen metagenome, metabolome, and HYK have not been well described. Therefore, the objective of this study was to compare rumen metagenome and metabolome profiles of cows with naturally occurring HYK to those without HYK during the first two weeks postpartum. Blood beta-hydroxybutyrate (BHB) concentrations at d 5, 10 and 14 postpartum were used to classify 16 rumen cannulated Holstein cows as either hyperketonemic (+ HYK; ≥1.2 mmol/L BHB at any of the collection days) or non-hyperketonemic (-HYK). Five + HYK cows were identified and were paired with 5 -HYK cows based on parity and calving date. Microbial DNA was extracted from rumen fluid and sequenced using shotgun metagenomics with the Illumina platform. Kraken2 was used to map reads to microbial taxonomic groups and Humann3.8 was used to predict potential functions. Metabolome profiling of rumen fluid was conducted using high-resolution liquid chromatography-mass spectroscopy. MetaboAnalyst6.0 was used to identify potential changes in metabolic pathways. Metagenomes and metabolomes comparisons were conducted using mixed models that included the fixed effects of group, day, their interaction, and the random effect of cow. There was minimal difference detected in alpha diversity for the metagenome, but differences in the metabolome were detected by HYK status. The concentration of asparagine and p-cresol was greater in + HYK cows compared to -HYK, but citrulline was greater in -HYK cows throughout all days considered. On d5 the concentration of ornithine was greater in + HYK compared to-HYK cows, and on d10 acetate was greater in the -HYK cows. There were no differences detected in the pathway analysis from the metabolites quantified by HYK status. Overall, modest differences in rumen metabolome were observed between + HYK and -HYK cows in early lactation. Future studies should explore associations between the rumen environment and HYK as this could be informative for treatment and management practices.