The objective was to determine if a 7-day lactic acid adaptation in cannulated steers affected ruminal fermentation during an acidosis challenge. Steers (n=18; 790 ± 68 kg) were assigned to one of two treatments: control (CON) 500 mL of H2O or 1 mM DL-Lactic acid solution per kg steer BW (LAC). Steers were dosed with treatments via the cannula prior to feeding for seven days during the adaptation period. The adaptation diet consisted of 25% corn silage, 30% grass hay, 15% dry distillers grains, 25% dry rolled corn, 5% molasses and 10% supplement. To induce acidosis, steers were fasted for 24 hours and subsequently fed a high concentrate diet consisting of 15% corn silage, 15% dry distillers grains, 55% high moisture corn, 5% molasses, 10% supplement. Rumen fluid was collected throughout the acidosis challenge to measure fermentation characteristics including rumen pH, redox, ammonia, volatile fatty acids, and lactic acid. Data were analyzed using the MIXED procedure of SAS 9.4 with a repeated measures analysis. Dry matter intake was not affected (P ≥ 0.65) by treatment before or after the acidosis challenge. A treatment × time interaction was not observed (P = 0.83) for ruminal pH, but pH was affected (P < 0.01) by time and remained between 5.6 and 5.0 for about 14 hours during the challenge. A treatment × hour interaction tended (P = 0.08) to be observed for lactate; LAC had a greater concentration than CON at hour 14 during the challenge. However, a treatment × hour interaction was not detected (P ≥ 0.38) for ammonia, volatile fatty acids, fecal pH and redox potential. In conclusion, these results indicate that a 7-day lactic acid adaption at 1 mM per kg BW did not affect ruminal fermentation characteristics during an acidosis challenge.

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.

The objective was to evaluate the effect of Propionibacterium acidipropionici P169 (PA) concentration on fermentation characteristics in a ruminal acidosis in vitro model. Ruminal acidosis is a common metabolic disorder in feedlot cattle characterized by a low rumen pH. The experiment included 5 treatments in a completely randomized design. Treatments included a negative control (NCON), 5 × 105 colony forming units (CFU) PA (PA5), 5 × 106 CFU PA (PA6), 5 × 107 CFU PA (PA7), and a positive control with greater forage inclusion (PCON). Flasks for NCON, PA5, PA6, and PA7 contained 8.75 g of substrate (70% corn, 15% DDG, 15% silage) while substrate for PCON flasks contain additional silage (40% corn, 15% DDG, 45% silage). Treatments were run in duplicate and the experiment was replicated 3 times. All flasks included 175 mL of inoculum (4 McDougall’s buffer:1 rumen fluid). Flasks were incubated at 39◦C for 36 hours and sample aliquots were collected every 4 hours. The MIXED procedure of SAS 9.4 was used for statistical analysis with a repeated measures analysis. A treatment by hour interaction (P < 0.01) was observed for pH; at hour 8, PCON was the least and PA5 was the greatest. From 20 to 36 h, PCON had the greatest pH. There was no treatment by hour interaction (P = 0.99) observed for redox potential. However, treatment affected (P < 0.01) redox potential with PCON being greater than PA6, PA7, and NCON, with PA5 being intermediate. In vitro dry matter disappearance (IVDMD) tended (P = 0.09) to be affected by treatment; PA5, PA6, and PA7 were greater than PCON. In conclusion, Propionibacterium acidipropionici P169 concentrations affected IVDMD, pH, and redox in a ruminal acidosis in vitro model.