Effects of Ruminal Acidosis on Rumen Papillae Transcriptome

Mackey, Emily
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University of Delaware
The objectives of this study were to first develop a feeding strategy to induce subacute ruminal acidosis (SARA) in dairy cows and then to measure the differential gene expression occurring in rumen mucosa of dairy cows undergoing SARA through transcriptome analysis using RNA-sequencing technologies. Six ruminally cannulated cows were paired based on days in milk and assigned to either a control or SARA treatment for a 15 day trial. Control cows were fed a standard ration ad libitum throughout the trial. SARA cows were fed a standard ration ad libitum d1-5 and d11- 15, 50% feed restricted on d 6, and fed a high grain diet ad libitum (50:50 ground wheat and barley mix at 20% of ration DM) d7-10 or until plasma fibrinogen levels rose above 150 mg/dL. Rumen pH was monitored continuously from d5-15. Dry matter intake and milk yield were recorded daily. Rumen fluid and fecal samples were taken on d 5, 7, 8, and 12 at 4 time points for volatile fatty acid analysis. Rumen papillae biopsies were extracted from the ventral sac of the rumen on d 5, d 8, and d 15 for histological and gene expression analysis. Rumen mean pH was found to be lower than control cows and SARA cows spent an overall increased time numerically under pH 5.6 (260min/d) in comparison to control cows (78min/d) during the challenge period. Dry matter intake was lower for SARA cows during post-challenge. Milk yield was lower for SARA cows during the challenge period and tended to be lower during post-challenge. Rumen butyrate, rumen lactate, and fecal lactate increased in response to treatment. Histological analysis showed there was no effect of treatment microscopically apparent in the rumen mucosa. Through transcriptome analysis, 172 genes were found to be differentially expressed because of treatment during the challenge period (d8). Of these genes, the molecular pathway of homophilic cell adhesion was upregulated in SARA cows indicative of a structural response in rumen mucosa tissue to oppose the creation of a weakened permeability barrier caused by an inflammatory response. Based on the intraruminal and symptomatic changes seen in SARA treated cows, we can conclude that we successfully induced SARA. This SARA treatment did not cause microscopically apparent changes in the rumen mucosa, but did cause an upregulation of genes involving maintaining cell adhesion.