Changes in meta-transcriptome of rumen epimural microbial community and liver transcriptome in young calves with feed induced acidosis.

Authors: Li, Wenli; GELSINGER, SONIA - University Of Wisconsin; EDWARDS, ANDREA - University Of Wisconsin; RIEHLE, CHRISTINA - University Of Wisconsin; KOCH, DANIEL - University Of Wisconsin

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2019
Publication Date: 12/12/2019
Citation: Li, W., Gelsinger, S., Edwards, A., Riehle, C., Koch, D. 2019. Changes in meta-transcriptome of rumen epimural microbial community and liver transcriptome in young calves with feed induced acidosis.. Scientific Reports. 9. Article 18967. https://doi.org/10.1038/s41598-019-54055-8.
DOI: https://doi.org/10.1038/s41598-019-54055-8

Interpretive Summary: Ruminal acidosis is a well-recognized digestive disorder found in dairy cattle. Although the consumption of starter feed may seem beneficial to rumen development, calves fed starch sources during the weaning transition exhibited increased volatile fatty acids production, leading to decreased ruminal pH and subsequent development of sub-acute ruminal acidosis (SARA). There is no typical clinical signs of illness in cows with SARA, and the currently defined clinical signs are generally delayed in onset from the time of low ruminal pH insult. Furthermore, the commonly used method for the diagnosis of ruminal acidosis relies on ruminal pH measurement though it lacks the accuracy and sensitivity leading to the non-diagnosis in many cases. Thus, there is a clear need for the development of sensitive biomarkers that can improve early diagnosis and preventative management. In this study, we specifically focused on the global transcriptome changes and impacted molecular pathways in liver tissues collected from four month old calves, with the goal of identifying differentially expressed mRNA transcripts that can be further developed into diagnostic biomarkers. This work was done using a model of feed-induced acidosis in newborn bull calves beginning at one week of age through 16 weeks. We hypothesized that significant changes in liver transcriptome were related to the rumen microbial community alterations, which were resultant from the feed-induced acidosis. This study helps the identification of highly effective, mRNA-based biomarkers that can aid the early diagnosis and prevention of feed-induced acidosis in dairy cattle.

Technical Abstract: The common management practices of dairy calves leads to increased starch concentration in feed, which subsequently may cause ruminal acidosis while on milk and during weaning. Ruminal pH has long been used to identify ruminal acidosis. However, few attempts were undertaken to understand the role of prolonged ruminal acidosis on host health in young calves long after weaning. Thus, the molecular changes in the liver associated with prolonged rumen acidosis in post weaning young calves are largely unknown. In this study, we induced ruminal acidosis by feeding a highly processed, starch-rich diet to calves starting from one week of age through 16 weeks. Liver tissues were collected at necropsy at 17 weeks of age from 8 calves (4 of them were treated; the remaining 4 were control). Transcriptome analyses on the liver tissues were carried out along with the meta-transcriptome analysis on the rumen epimural microbial community. Calves with induced ruminal acidosis showed significantly less weight gain over the course of the experiment, in addition to substantially lower ruminal pH in comparison to the control group (p<0.05). For liver transcriptome, a total of 428 genes (fold-change, FC ' 1.5; adjusted-pvalue ' 0.1) showed significant differential expression (DE) in comparison to control. Biological pathways impacted by these DE genes included cellular component organization, indicating the impact of ruminal acidosis on liver development in young calves. Specifically, the up-regulated genes were enriched in acute phase response (p-value<0.01), pyruvate metabolic process (p-value<0.01) and proton-acceptors (p<<0.001), indicating the liver’s response to feed induced acidosis at the transcriptome level. Twelve liver transferase activity related genes had significant correlation with rumen microbial rRNA expression changes (pearson's r analysis, p <0.0001), indicating the direct effect of feed-induced acidosis on both the rumen microbial community and liver metabolism. Our study provides insight into the physiological remodeling in the liver resultant from the prolonged acidosis in post weaning calves. Such knowledge provides a foundation for future molecular-based diagnosis and preventative management of rumen acidosis in dairy calves.