Changes in the Fermentation and Bacterial Community by Artificial Saliva pH in RUSITEC System

Abstract

The purpose of the study was to assess the artificial saliva (AS) pH on ruminal fermentation and rumen bacteria community in the rumen simulation technique (RUSITEC) system. The experiment was performed in two treatments (low AS pH vs. high AS pH) with four replicates. The low AS pH was sustained by altering the composition of the AS (NaHCO3 from 9.8 to 1.96 g/L, Na2HPO4 from 9.3 to 1.86 g/L) according to McDougall's method. The diets were supplemented with 16 g basic diets with forage to the concentrate ratio of 50:50. The experiments were conducted over 13-day incubation periods, with 9 days adaption and 4 days sample collection. The results showed low AS pH decreased dry matter (DM) degradability (64.37 vs. 58.67%), organic matter (OM) degradability (64.38 vs. 59.32%), neutral detergent fiber (NDF) degradability (46.87 vs. 39.94%), acid detergent fiber (ADF) degradability (38.16 vs. 31.13%), and crude protein (CP) degradability (70.33 vs. 62.99%), respectively. Compared with the high AS pH, the low AS pH increased the proportion of butyrate (P = 0.008) and decreased the proportion of propionate (P < 0.001). At the bacteria community, the low AS pH increased the abundances of Spirochaetes (P = 0.001) and Synergistetes (P = 0.004) and decreased the Verrucomicrobia abundance (P = 0.004) in solid-associated bacteria. At the genus level, the low AS pH increased the abundance of Lactobacillus (P = 0.050) and decreased the abundance of Schwartzia (P = 0.002) in solid-associated bacteria. The abundances of Prevotellaceae_YAB2003_group (P = 0.040), Schwartzia (P = 0.002), and Ruminobacter (P = 0.043) were lower in the low AS pH group compared with the high AS pH group in liquid-associated bacteria. Low AS pH decreased the number of Ruminococcus albus, Ruminococcus flavefaciens, Fibrobacter succinogenes (P < 0.001) both in the solid- and liquid-associated bacteria, respectively. The results of the present study included three groups of bacteria communities according to the different sensitives to rumen pH: the abundances of Lactobacillus, Succinivibrio, and Prevotella_7 are increased with decreasing AS pH; the amounts of R. albus, R. flavefaciens, F. succinogenes as well as the abundances of Schwartzia and Ruminobacter decreased with the reducing AS pH; the abundances of Selenomonas_1, Rikenellaceae_RC9_gut_group, and Succiniclasticum were not affected by the AS pH in RUSTITEC.

Rumen Bacteria Abundance and Fermentation Profile during Subacute Ruminal Acidosis and Its Modulation by Aspergillus oryzae Culture in RUSITEC System

“…Low AS pH group significantly decreased the abundance of Proteobacteria from 14.6% to 0.96% compared with the high AS pH group, which was an agreement with Mao et al [3], who found that feeding SARA diets in cattle decreased the abundance of Proteobacteria. Nevertheless, this is in contrast with findings of Guo et al [42], who found that the abundance of Proteobacteria was greater in low AS pH at 6.02 in RUSITEC system. Combined with other studies, the results indicated that Proteobacteria was more sensitive to rumen pH; the growth and activity of Proteobacteria was inhibited by low AS pH 5.5, while it increased in low AS pH 6.02.…”

“…The molar proportion of propionate was decreased in the low AS pH group, but the molar proportion of acetate was not affected, which resulted in increasing the ratio of acetate to propionate. These results are similar to an earlier study in our lab [42]. The difference in the molar proportion of propionate may be relate to the reduction of starch digestion.…”

“…In the present study, the three main phylum Bacteroidetes, Firmicutes, and Proteobacteria were altered by the low AS pH. The abundance of Bacteroidetes did not differ among the treatments according to Brede et al and Guo et al [42,46], who found the abundance of Bacteroidetes was not altered by the SARA challenge or low AS pH at 6.0 in RUSITEC system. However, these results were in contrast to some previous studies, which reported a decrease in the abundance of the phylum Bacteroidetes during SARA challenges [3,7].…”

“…Mao et al reported that the Firmicutes was more abundant in cattle fed SARA diets compared with the control diets [3]. Guo et al found that the abundance of Firmicutes was not affected by AS pH at 6.02 in RUSITEC [42]. In this experiment, decreasing AS pH at 5.5 increased the abundance of Firmicutes.…”

Supplementation of Aspergillus oryzae Culture Improved the Feed Dry Matter Digestibility and the Energy Supply of Total Volatile Fatty Acid Concentrations in the Rumen of Hu Sheep

“…The variation in the present study was the dosage of AOC. Due to the stability of the microbial community in the rumen ( 34 ), the results of β-diversity were also understandable.…”