Controlled Ruminal Infusion of Sodium Bicarbonate. 2. Effects of Dietary and Infused Buffer 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 NaHCO₃ infusion on ruminal environment of cows receiving dietary sodium bicarbonate. Sodium bicarbonate (110 g) was mixed with 3.8 L of water and infused at a constant rate into the rumen from 0 to 2, 2 to 4, or 4 to 6 h postfeeding twice daily. All cows were fed sorghum silage and concentrate in a 35:65 DM ratio for 45 min twice daily. Ruminal fluid was collected at feeding and every 30 min postfeeding for 8 h on the last day of each 1-wk experimental period. Dry matter intake was not affected by NaHCO₃ infusion. Yields of mik and its components were reduced with 4- to 6-h NaHC03 infusion. At certain isolated times, especially during infusion, NaHCO₃ infusion increased ruminal fluid buffer. Concentrations of ruminal fluid total VFA were not affected by NaHCO₃ infusions, whereas acetate to propionate ratio tended to be reduced. Ruminal liquid volume tended to be increased by 0- to 2-h NaHCO₃ infusion, and ruminal outflow rate tended to be reduced by the 2- to 4-h infusion. Intraruminal infusion of NaHC0₃ into cows receiving supplemental dietary NaHCO₃ altered ruminal acid-base status as typically reported for those receiving dietary NaHCO₃; however, these alterations were not accompanied by shifts in ruminal VFA patterns or in milk composition that normally result from such feeding regimens. The effects of NaHCO₃ infused directly into the rumen may be different from those of dietary NaHCO₃ and are possibly related to the different time of entry into the rumen relative to feeding.

Key Words: sodium bicarbonate • rumen pH • buffering capacity

Submitted on December 10, 1990
Accepted on May 16, 1991