Associations of ruminal microbiota with susceptibility to subacute ruminal acidosis in dairy goats.

Long-term feeding of high-concentrate diets (HCD) to ruminants often leads to subacute ruminal acidosis (SARA). The fact that some ruminants adapt to HCD without developing SARA suggests that the ruminal microbiota communities may play a role in the susceptibility to this disorder. To address this hypothesis, 20 dairy goats were fed an HCD consisting of 30 % forage and 70 % concentrate for 10 weeks. The dairy goats were divided into a SARA susceptible group (SS, pH < 5.8 for more than 3 h within 12 h) and a SARA tolerant group (ST, pH < 5.8 for not more than 3 h within 12 h) according to ruminal fluid pH. At 0 and 10 weeks after feeding with HCD, blood samples were collected via the jugular vein using a vacutainer to assess the levels of white blood cells, neutrophils, and lymphocytes. Meanwhile, milk samples were collected to measure milk composition. In addition, ruminal fluid was collected via a gastric tube at 0 and 10 weeks of feeding the experimental diets via gastric tube and the ruminal microbiota of SS and ST dairy goats were analyzed. The results indicated that feeding with HCD led to greater levels of white blood cells, neutrophils, creatinine, and urea nitrogen, and lower concentrations of milk fat. Further, levels of white blood cells and neutrophils were greater in SS compared with ST goats. The 16S rRNA sequencing analysis revealed that the diversity and abundance of the ruminal bacterial community was lower in SS compared to ST goats. Furthermore, the relative abundance of norank_f_F082, norank_f_Bifidobacteriaceae, and the genus Ruminococcus was higher in the SS group. These microorganisms are important for the digestion of non-structural carbohydrates and the production of volatile fatty acids (VFA). The initial ruminal microbiota composition analysis revealed that Rikenellaceae_RC9_gut_group was greater in ST goats, both before and after feeding HCD. By promoting carbohydrate metabolism in the rumen, the data suggest that the increased abundance of norank_f_F082, Ruminococcus and UCG-004 may lead to the production of metabolites that increase susceptibility to SARA when fed HCD. Enrichment of ruminal bacteria such as Rikenellaceae_RC9_gut_group may reduce susceptibility to SARA in HCD diets. Overall, manipulation of the ruminal microbiota may be a novel approach to prevent the development of SARA in ruminants.