THE INFLUENCE OF BICARBONATE BUFFERS ON MILK PRODUCTION AND ACID-BASE BALANCE IN LACTATING DAIRY COWS

Abstract

Two 4 × 4 Latin square feeding trials were conducted to investigate the influence of 0.75% sodium bicarbonate (NaHCO3), 0.75% potassium bicarbonate (KHCO3) and 0.66% ammonium chloride (NH4Cl) on production and acid-base parameters of dairy cows. Buffer supplementation did not improve feed intake or milk production compared to the control ration of 50% concentrate, 50% barley silage (DM basis). Apparent digestibilities of dry matter, acid detergent fiber and crude protein were not influenced by treatment. Buffer supplementation resulted in an increase in milk fat and total solids content in trial 2 but not in trial 1. In comparison to the two buffered rations, NH4Cl induced a mild form of acidosis as evidenced from reduced (P < 0.05) blood pH, HCO3, BE and urine pH values in trial 1 and blood HCO3 and urine pH in trial 2. In addition, DM and concentrate intake were reduced in trial 2 with NH4Cl supplementation. Treatment did not affect the molar proportions of the major rumen volatile fatty acids (VFA). It is concluded that milk fat production did not respond as expected to buffer supplementation due to a failure to influence the pattern of rumen VFA production. The control ration did not stress the acid-base homeostasis of the animal. Consequently, buffer supplementation did not lead to any improvement in systemic acid-base status. Key words: Dairy cattle, milk production, potassium and sodium bicarbonate, ammonium chloride, acid-base balance