Controlled Ruminal Infusion of Sodium Bicarbonate. 3. Influence of Infusion Dose on Systemic Acid-Base Status, Minerals, and 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 effects of intraruminal NaHCO₃ infusion on temporal changes in ruminal and systemic acid-base status and mineral metabolism. Twice daily from 2 to 4 h postfeeding, cows were infused with 0, 110, 220, or 330 g of NaHCO₃ dissolved in 3.8 L of water. All cows had access to their TMR of sorghum silage and concentrate (35: 65, DM basis) for 2 h twice daily. Ruminal fluid, blood, and urine were collected at feeding and every 30 min postfeeding for 12 h on the last day of each 14-d period. Total urine volume also was measured during this interval. Infusion of buffer increased ruminal fluid buffering capacity transiently at 4.5 h postfeeding but otherwise did not markedly affect ruminal fluid acid-base status. Systemic acid-base status was unaffected by the buffer primarily because renal excretion of base successfully reduced systemic base load. Urine volume increased in response to NaHCO₃ infusion. Buffer infusion increased urinary excretion of Na, Mg, and K but decreased Ca excretion for 12 h postfeeding; C1 excretion was not affected. Buffer infusion tended to increase total VFA in ruminal fluid. Our data indicate that homeostatic mechanisms can eliminate exogenous base via the kidneys; hence, acid-base status was not perturbed by infusion of NaHCO₃. The increased excretion of Mg and K with buffer infusion indicates that the dietary requirements for these minerals may be increased by NaHCO₃. Although loss of Ca through the urine was reduced by buffer infusion, this reduction may indicate reduced availability of Ca to the cow. The diuresis accompanying large doses of NaHCO₃ may increase dietary requirements for some minerals.

Key Words: sodium bicarbonate • ruminal pH • buffering capacity • minerals

Submitted on June 9, 1992
Accepted on February 16, 1993

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