241 Evaluating the Effects of Lactate Adaptation in Cannulated Steers on Fermentation Characteristics in an Ex Vivo Model of Ruminal Acidosis

Abstract The objective was to determine if lactate adaption in cannulated steers affected fermentation characteristics in an ex vivo model of ruminal acidosis. Eighteen cannulated steers (790 ± 68 kg) were assigned to 1 of 2 treatments: 500 mL of H2O (CON) or 1 mM DL-Lactic acid solution per kg steer BW (LAC). After treatments were dosed prior to feeding for 6 d, rumen fluid was collected for an ex vivo study. Three flasks for each steer contained 7.5 g DM of substrate (70% corn, 15% DDG, and 15% silage) and 160 mL of inoculum with rumen fluid and McDougall’s buffer (4:1 ratio). Sample aliquots (1.7 mL) were collected every 4 h from the flask for 36 h fermentation for later analysis. At 12 h, 90 mM of neutralized DL-Lactic acid was added to each flask to further evaluate lactate utilization over time. Data were analyzed using the MIXED procedure of SAS 9.4 with a repeated measures analysis. A treatment by hour interaction was not detected (P = 0.19) for pH. However, steers on LAC tended (P = 0.06) to have a greater pH than CON. No treatment by hour interaction or treatment effect was observed (P ≥ 0.44) for molar proportion of acetate, propionate, butyrate, and ammonia. A treatment by hour interaction tended (P = 0.07) to be observed for total VFA; CON was greater than LAC at hour 8, 13, 16, and 20. Control steers had a greater (P = 0.03) in vitro dry matter disappearance compared with LAC (63.6 vs. 54.0%, respectively). Although results indicated that rumen fluid from lactate-adapted steers had a greater pH in an acidosis model, rumen fluid from CON steers had improved IVDMD and total VFA concentrations.