Efficacy of simulated, slow release sodium bicarbonate in stabilizing ruminal milieu and acid-base status in...

Four primiparous, ruminally fistulated, lactating Holstein cows were assigned to a 4 X 4 Latin square to study the effects of NaHCO3 infusion time on ruminal milieu and systemic acid-base balance. Sodium bicarbonate, approximating .8% of diet DM, was mixed with water and infused into the rumen for 1, 2, 4, or 6 h postfeeding to simulate different timed-release rates of NaHCO3. All cows received a corn silage and concentrate diet mixed at a 40:60 ratio on a DM basis and fed in amounts that were consumed within 1 h. Ruminal fluid, blood, and urine samples were collected at 0, 1, 2, 3, 4, 5, 6, 8, and 10 h postfeeding. Length of infusion time did not alter ruminal, blood, or urine pH, but all three variables were affected by sampling time, with the 5, 1, and 3-h sampling intervals yielding the lowest values for the three measurements, respectively. Ruminal VFA molar percentages of acetate, propionate, butyrate, isovalerate, and valerate were not influenced by infusion interval but were all different due to time of sampling. Blood pCO2 and HCO3 were affected by sampling time but not by infusion interval. With the exception of blood HCO3, all treatment X sampling time interactions were nonsignificant. It appears that timed release of NaHCO3 does not alter ruminal function or acid-base balance.