Controlled Ruminal Infusion of Sodium Bicarbonate. 1. Influence of Postfeeding Infusion Interval on Ruminal Milieu

¹ Animal Science Department, Oklahoma State University, Stillwater 74078

Four ruminally cannulated, lactating Holstein cows were assigned to a 4 x 4 Latin square to monitor the effects of intraruminal NaHCO₃ infusion on changes in the rumen environment. Sodium bicarbonate (110 g), dissolved in 3.8 L of water, was infused twice daily at a constant rate for 2 h starting at 0, 2, or 4 h postfeeding. All cows had access to their diet containing sorghum silage and concentrate in a 35:65 ratio (DM basis) for 45 min twice daily. Ruminal fluid was collected at feeding and every 30 min postfeeding for 12 h on the last day of each 7-d period. Dry matter intake was lower for buffer infusion at 2 to 4 h than for water-infused control but was not affected by the other NaHCO₃ infusions. Although total milk yield was not affected, milk fat percentage and fat yield tended to be lower for the NaHCO₃ treatments. Compared with the water infusion, the NaHCO₃ infusion from 2 to 4 h postfeeding most effectively prevented the postfeeding increase in ruminal free proton concentration. Additionally, volume of ruminal liquid was increased for the NaHCO₃ infusions from 0 to 2 h and 4 to 6 h; ruminal liquid turnover time was increased for the NaHCO₃ infusion at 4 to 6 h, but ruminal kinetics otherwise were not affected by NaHCO₃. Although infusion of NaHCO₃ from 2 to 4 h prevented severe alterations in ruminal acid-base status. it did not increase total VFA concentration or the acetate:propionate ratio. Although total VFA concentrations were not affected by NaHCO₃ infusion, acetate:propionate ratio was higher for the NaHCO₃ infusion from 0 to 2 h than for the control. Based upon alterations in ruminal acid-base status, exogenous buffer ideally should be provided to the rumen from 2 to 4 h postfeeding; however, our results indicate that the effectiveness of this regimen might be improved if buffer is combined with a rapidly released or unprotected dietary buffer.

Key Words: sodium bicarbonate • rumen pH • buffering capacity

Submitted on October 12, 1990
Accepted on December 26, 1990

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