Liver microbial community and associated host transcriptome in calves with feed induced acidosis

Authors: Li, Wenli; LARSEN, ANNA - Oak Ridge Institute For Science And Education (ORISE); MURPHY, BRIANNA - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Calves fed a highly fermentable diet during the weaning period are the most vulnerable to developing ruminal acidosis. Prevalent in cattle, liver abscesses are ancillary to ruminal acidosis. Liver abscesses can cause significant economic losses to producers as the result of liver function condemnation and decreased growth and production. However, liver abscesses are only identified at the time of culling due to the lack of early diagnostic tools available for the detection or prevention of liver abscesses. We have established a model of feed-induced ruminal acidosis in young calves using an acidosis-inducing or -blunting (control) diet. Using this model, we investigated the impact of ruminal acidosis on the microbial community in the liver and rumen, as well as changes in gene expression in the host liver. We detected significant changes in the microbial communities of both the rumen epithelium and the liver under the acidosis-inducing diet, including an increase in several microbial genera previously associated with liver abscesses in adult cattle. Changes in the expression of genes related to energy and lipid metabolism were also detected in the host liver. Notably, none of the calves in the study showed any clinical signs of liver abscess, yet a significant shift in the liver microbial community was observed in calves fed the acidosis-inducing diet compared to the control group at an early age. The concurrent shifts in microbial community changes 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 microbial community in the progression of ruminal acidosis. Furthermore, this research suggests microbial biomarkers circulating in the blood through the liver could be developed as detection tools for early intervention and management of liver abscesses.

Technical Abstract: In the dairy industry, calves are typically managed to maximize ruminal papillae and tissue development by feeding diets that are rich in highly fermentable carbohydrates and low in fibrous feeds. Calves fed a highly fermentable diet during the weaning period are the most vulnerable to developing ruminal acidosis. Prevalent in cattle, liver abscesses (LAs) are considered ancillary to ruminal acidosis. LAs can cause significant economic loss as the result of liver function condemnation and decreased growth and production. Currently, there are no early diagnostic tools available for the detection or prevention of LAs. We have established a model of ruminal acidosis in young calves using an acidosis-inducing (AC) or -blunting (control) diet. Using this model, we investigated the impact of ruminal acidosis on the microbial community in the liver. Eight calves were randomly assigned to each diet, with four animals per treatment. Rumen epithelium and liver tissues were collected at 17 weeks of age right after euthanasia. Total RNAs were extracted and followed by whole transcriptome sequencing. Calves with induced ruminal acidosis showed significantly less weight gain over the course of the experiment, in addition to substantially lower ruminal pH, and significant rumen degradation compared to the control group (P<0.05). Microbial RNA reads were enriched bioinformatically and used for microbial taxonomy classification using Kraken2. In the liver, a total of 29 genera showed a significant (P<0.05) abundance change (>2-fold) between the treatments. Among these, Fibrobacter, Treponema, Lactobacillus, and Olsenella have been reported in abscessed liver in cattle. Nine of the genera were also identified in the rumen epithelium with a significant increase (P<0.05, >2-fold) in abundance in the AC group in both tissues. Host liver genes involved in pyruvate metabolic processes (including proton-acceptors) and lipid metabolism pathways showed significant association (P < 0.01) with the microbial community changes. Our study sheds light on host liver community changes associated with prolonged acidosis in post-weaning calves. Notably, none of the calves in the study showed any clinical signs of liver abscess, yet a significant shift in the liver microbial community was observed in calves with the acidosis-inducing diet compared to the control group. 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.