Liver microbiome changes identified by transcriptome sequencing in young calves with feed induced acidosis

Liver abscesses (LAs) are ancillary to ruminal acidosis and can cause significant economic loss as the result of liver function condemnation and decreased growth and production. Currently, there are no effect diagnostic tools for early detection or prevention of LAs. Using our established model of ruminal acidosis in young calves, we investigated the effect of ruminal acidosis on the microbial community in the liver. A group of 8 calves were randomly assigned to an acidosis-inducing diet (AC) or blunting diet, with 4 animals per treatment. Rumen epithelium and liver tissues were collected at 17 wk of age right after slaughter. Total RNAs were extracted and followed by whole transcriptome sequencing. Calves fed AC showed significantly less weight gain over the course of the experiment, substantially lower ruminal pH, and significant rumen degradation comparison to the control group (P < 0.05). Microbial RNA reads were enriched bioinformatically and used for microbial taxonomy classification using Kraken2, and transcript abundance analysis. In the liver, a total of 29 genera showed more than 2-fold change in abundance between the treatments. Among these, Fibrobacter, Treponema, Lactobacillus, and Olsenella have been reported in abscessed liver in cattle. Additionally, 9 of these genera also significantly increased in the rumen epithelium (P < 0.05, fold change >2) in the AC group. In the liver, genes involved in pyruvate metabolic process, proton-acceptors and lipid metabolism pathways had significant association with the microbial community changes. Our study sheds light into host liver community changes in postweaning calves with prolonged acidosis. The concurrent shifts in microbial genus abundance in both the liver and rumen indicate potential crosstalk between the liver and rumen epithelial microbial communities. Given the important role of the liver as a metabolic organ, our findings warrant further investigation into the role of the liver microbiome in the progression of ruminal acidosis and the specific molecular events that facilitate the interactions between the gut and the liver.

Key Words: ruminal acidosis, liver microbiome, young calves.

Presented at the 10th Symposium on Gut Health in Production of Food Animals 2022, St. Louis, USA.