Effects of Ruminal Acidosis on Rumen Papillae Transcriptome
Date
2013-05
Authors
Mackey, Emily
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
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.