Diet Transition from High-Forage to High-Concentrate Alters Rumen Bacterial Community Composition, Epithelial Transcriptomes and Ruminal Fermentation Parameters in Dairy Cows

Abstract

Simple Summary Cattle are fed a high-concentrate diet to improve their productivity; however, it alters the rumen ecosystem due to high structural carbohydrates level, resulting in ruminal acidosis. This study investigated the effect of changing diet on ruminal fermentation parameters, bacterial community composition, and expressed genes of Holstein Friesian cows, with changes induced by transition from a high-forage to two succeeding high-concentrate diets, and then returned to a high-forage diet. Ruminal pH drastically decreased; however, ammonia nitrogen, and individual and total volatile fatty acid (VFA) concentrations increased during the high-concentrate diet period. High-concentrate diet also reduced rumen bacterial richness and diversity. Gene expression in rumen epithelia was affected and altered by changing diet through the obtained differentially expressed genes. Effects of changing diet on rumen fermentation parameters, bacterial community composition, and transcriptome profiles were determined in three rumen-cannulated Holstein Friesian cows using a 3 x 4 cross-over design. Treatments include HF-1 (first high-forage diet), HC-1 (first high-concentrate diet), HC-2 (succeeding high-concentrate diet), and HF-2 (second high-forage diet as a recovery period). Animal diets contained Klein grass and concentrate at ratios of 8:2, 2:8, 2:8, and 8:2 (two weeks each), respectively. Ammonia-nitrogen and individual and total volatile fatty acid concentrations were increased significantly during HC-1 and HC-2. Rumen species richness significantly increased for HF-1 and HF-2. Bacteroidetes were dominant for all treatments, while phylum Firmicutes significantly increased during the HC period. Prevotella, Erysipelothrix, and Galbibacter significantly differed between HF and HC diet periods. Ruminococcus abundance was lower during HF feeding and tended to increase during successive HC feeding periods. Prevotella ruminicola was the predominant species for all diets. The RNA sequence analysis revealed the keratin gene as differentially expressed during the HF diet, while carbonic-anhydrase I and S100 calcium-binding protein were expressed in the HC diet. Most of these genes were highly expressed for HC-1 and HC-2. These results suggested that ruminal bacterial community composition, transcriptome profile, and rumen fermentation characteristics were altered by the diet transitions in dairy cows.