Alterations in fermentation parameters during and after induction of a subacute rumen acidosis in the rumen simulation technique.

Subacute rumen acidosis (SARA) is a common problem in dairy cattle. High-concentrate rations lead to an accumulation of short-chain fatty acids (SCFA) in the rumen and a subsequent decrease in ruminal pH. As SARA impairs animal welfare and productivity, numerous in vivo studies are focusing on evaluation of prevention strategies. In vitro models can support this research and reduce animal numbers and experimental costs. We used different diets and buffer compositions to induce SARA in the rumen simulation technique (Rusitec) and investigated the recovery process. The experiment consisted of an equilibration period (7 days), a first control period, a SARA period and a second control period (5 days each). During the SARA period, SARA was induced by infusing SARA1 or SARA2 buffer with reduced bicarbonate (20 mmol/L and 25 mmol/L) and phosphate (both 10 mmol/L) contents compared to a modified McDougall's buffer (bicarbonate 97.9 mmol/L, phosphates 20 mmol/L). Additionally, we compared three feeding strategies, which differed in the concentrate-to-roughage ratio (30:70, 70:30, changing ratio: 30% concentrate in control periods and 70% concentrate in SARA period). During the SARA period, the pH decreased to a constant value below the SARA thresholds of pH 5.8 and 5.6, whereas lactate concentrations remained low. The total SCFA production rate declined 3 days after SARA induction, and the molar proportion of acetate decreased. The decrease in pH and SCFA production was more pronounced for SARA1 buffer. The high-concentrate diet reduced the molar proportion of acetate and increased NH -N concentrations. During the second control period, most parameters recovered. In conclusion, SARA conditions were successfully induced in the Rusitec. However, we observed a higher influence of buffer composition than of concentrate proportions on most biochemical parameters. Nearly all changes were reversible. This model can be applied to test acidosis prevention strategies prior to animal experiments.