Abstract:

This experiment was conducted to compare the morphology and function of rumen epithelium in dairy cows with differences in susceptibility to subacute ruminal acidosis （SARA）. Twelve multiparous fistulated Holstein cows in mid lactation were housed in individual stalls and fed a diet with a concentrate to forage ratio of 4∶6 throughout the experimental period. Based on the ruminal pH， cows with relatively lower and higher mean ruminal pH were assigned， respectively， to susceptible （SUS， n=4） and tolerant （TOL， n=4） groups. The examination of ruminal epithelial morphology and function revealed that the cells in the spinous process and basal layer of ruminal epithelium were thicker in the SUS than in the TOL group （P<0.05）. In the SUS group， the expression levels of PAT1， MCT4， and DRA genes involved in volatile fatty acid （VFA） absorption were significantly lower （P<0.05）， while the NHE1， NHE2， NHE3， vH⁺ ATPase， and Na⁺/K⁺ ATPase levels were significantly higher than in the TOL group （P<0.05）. The results of gene expression for ruminal VFA metabolism showed that PDHA1 and SREBP2 in the SUS group was higher （P<0.05）， while the expression of HMGCL-2 was significantly lower （P<0.05）. In addition， the expression levels of genes involved in the proliferation and apoptosis of rumen epithelial cells， such as CDK2， CDK6， Cyclin D1， Bad and Caspase-9 in the SUS group were higher in the SUS group than in the TOL group （P<0.05）. In summary， under the same diet， there was a lower expression of genes associated with free fatty acid absorption and a higher expression of genes related to non-free fatty acid absorption in rumen epithelial cells of SUS cows. This results in free fatty acid accumulation and reduced ruminal pH in the SUS group， and increased the risk of SARA in these cows.

Key words: dairy cows, subacute ruminal acidosis, tolerance, rumen epithelium