Effects of repeated subacute ruminal acidosis challenges on the adaptation of the rumen bacterial community in Holstein bulls

Abstract

We investigated the effect of repeated subacute ruminal acidosis (SARA) challenges on the pH, fermentative function, and bacterial community in the rumen. Four rumen-cannulated Holstein bulls were fed a high-forage diet for 7 d (HF period) followed by a high-grain diet for 7 d (HG period). Four SARA challenges were carried out consecutively (first, second, third, and fourth challenges). The ruminal pH was measured continuously during the experiment, and rumen fluid samples during the first to fourth challenges were collected at 0800, 1400, and 2000 h on the last days of each feeding period for analysis; volatile fatty acid components, NH-N, and lactic acid concentrations were measured. Bacterial community structure was analyzed at 0800 h during the first and fourth challenges on the last days of each period. The 24-h mean ruminal pH was decreased during the transition from high-forage to high-grain diet and tended to differ between the HF and HG periods. During the HG period, ruminal pH <5.6 was maintained for a longer period in the first and second challenges (350 and 405 min/d, respectively) than in the third and fourth challenges (both 120 min/d). A marked increase in total volatile fatty acid and NH-N concentrations during the HG period was observed in the later challenges. In addition, lower and higher proportions of acetic and butyric acids, respectively, were observed during the HG period than during the HF period. A total of 37 core bacterial genera were found in all samples; however, the relative abundance of several genera differed significantly between the HF and HG periods (Prevotella, Ruminococcus, Eubacterium, and Oscillibacter) and between the first and fourth challenges (Eubacterium and unclassified Clostridiaceae). During the HG period, lower relative abundances of Prevotella, Eubacterium, and Oscillibacter and higher relative abundance of Ruminococcus were detected compared with during the HF period. The relative abundances of Eubacterium and unclassified Clostridiaceae were lower in the first challenge than in the fourth challenge. Bacterial diversity was greater during the HF period than during the HG period and was greater during the fourth challenge than during the first challenge. Interestingly, diversity indices during the HG period of the fourth challenge were higher than those during the HF period of the first challenge. These results suggested that rumen fermentation in Holstein cattle can adapt to repeated SARA challenges by minimizing the adverse changes in ruminal pH. Moreover, the composition and diversity of the ruminal bacterial community may be affected by ruminal pH and vice versa.

Fermentation Pattern of Several Carbohydrate Sources Incubated in An in Vitro Semicontinuous System with Inocula From Ruminants Given Either Forage or Concentrate-Based Diets

“…The effect of the inoculum source was also observed in microbial diversity, suppporting the recent findings reported by Tapio et al [45] and Nagata et al [46] who showed the difference in the rumen microbial population when bulls were fed with forage or concentrate diets.…”

Effects of an increased concentrate diet on rumen pH and the bacterial community in Japanese Black beef cattle at different fattening stages

“…However, the bacterial diversity (OTUs, PD whole tree, Chao1, and Shannon index) did not differ between the two periods or between the two groups, although the indices in both groups were lower during the HC period compared with the CON period. The reduction in rumen pH in the Mid group during the HC period was severe enough (6.00 to 5.76) to reduce bacterial diversity compared with a previous study (6.52 to 6.10 [15]). Therefore, we postulate that the rumen of the Japanese Black beef cattle adapted to long-term feeding of a high-concentrate diet to minimize the adverse changes in the bacterial diversity.…”

“…Previously, Sato [21] suggested that feeding a high-concentrate diet can induce acidotic conditions via higher total VFA and lactic acid concentrations, which were consistent with the findings in our Late group. Although we could not fully explain the contrasting results between the middle and late fattening stages, the results suggest that the rumen is fully adapted to long-term acidic conditions during the late fattening stage, in line with a report that the rumen can adapt to SARA in Japanese Black cattle [15].…”

“…For example, feeding beef cattle a high-grain diet causes declines in rumen bacterial diversity [19] and cellulolytic bacteria in the rumen fluids [3]. The rumen can adapt to repeated SARA by minimizing the changes in rumen pH, which may affect the composition and diversity of the ruminal bacterial community or vice versa [15].…”

Evaluation of biochemical profile and rumen fluid parameters of sheep supplemented with Saccharomyces cerevisiae and subjected to an abrupt diet change

“…Ingestion of these carbohydrates can lead to changes in the rumen pH, with prolonged reductions to values below 6.0. This new environment promotes the growth of amylolytic bacteria and inhibits the growth of cellulolytic bacteria, causing direct negative effects on digestibility (Nagata et al, 2018). On the other hand, rumen pH values below 5.8 increase the production of short-chain fatty acids (SCFA) and the proliferation of lactate-using bacteria (Bannink, France, & Lopez, 2008), making this value a threshold of vulnerability for the epithelium.…”