Effects of different dietary concentrate to forage ratio and thiamine supplementation on the rumen fermentation and ruminal bacterial community in dairy cows

A subacute ruminal acidosis (SARA) model was induced gradually by increasing the proportion of dietary concentrate to evaluate the effect of thiamine supplementation on the structure of bacterial community in dairy cows. Three Holstein dairy cows with rumen cannula were randomly assigned to a replicated 3 x 3 Latin square design trial and received three diets during three successive 21-day periods in each square. The three dietary treatments were as follows: a low-concentrate diet (control), a high-concentrate SARA-induced diet (SARA) and a high-concentrate SARA-induced diet with 180 mg thiamine/kg DM (SARA+ thiamine). Real-time-polymerase chain reaction assay was used to quantify the population variation of SARA-related ruminal bacteria in these cows. The results showed that SARA was induced gradually when cows were fed with the high-concentrate diets. The mean ruminal pH value was higher in the control cows than in those of SARA and SARA+ thiamine groups, the mean was decreased in cows fed on SARA diet, and the depression was alleviated by supplemented thiamine and the difference was significant (P < 0.05) especially at 9-h and 12-h sample times (or 1 h and 4 h after the second feeding). The populations of Streptococcus bovis and genus Lactobacillus in cows from the SARA group were increased in log copies/mL by 3.62% and 4.65%, respectively, compared with the control group (P < 0.05). In contrast, in log copies/mL, populations of Butyrivibrio fibrisovens and Megasphaera elsdenii were decreased by 1.14% and 4.90%, respectively (P < 0.05). Thiamine supplementation led to an obvious reduction of Strepococcus bovis and Lactobacillus (P < 0.05), whereas the number of log copies/mL of Megasphaera elsdenii was dramatically increased (P < 0.05). There was no significant effect of thiamine supplementation on the number of log copies/mL of Butyrivibrio fibrisovens and Selenomonas ruminantium (P > 0.05). It was concluded that thiamine supplementation to high-concentrate diets at concentrations of 180 mg/kg DM could help alleviate SARA by increasing rumen pH and balancing the population of lactic acid-producing and -consuming bacteria.