Effect of dietary sodium bicarbonate and magnesium oxide on production and physiology in early lactation.

Twenty cows were in an experiment to measure effects of dietary buffers, sodium bicarbonate and magnesium oxide, on ration adjustment and incidence of metabolic problems in the first 8 wk postpartum. Cows were fed 2.7 kg grain per day and alfalfa ad libitum prepartum and switched immediately to a complete ration of 40% corn silage and 60% concentrate (dry matter) postpartum. Treatments included 1.5% sodium bicarbonate and .8% magnesium oxide (total ration dry matter) fed in a 2 x 2 factorial arrangement. Cows receiving bicarbonate peaked 2 to 3 wk earlier in intake and averaged 2.1 kg per day greater intake than those fed the control diet. Actual milk production was increased by sodium bicarbonate with greatest differences for cows receiving both buffers averaging 3.8 kg per day more milk than control cows. Increases over co ntrols were 2.6 and 5.6 kg fat-corrected milk per day for cows receiving sodium bicarbonate alone or in combination with magnesium oxide, respectively. Sodium bicarbonate increased acetate to propionate molar ratios in rumen samples taken at 1 and 2 wk postpartum whereas neither buffer had any effect on rumen pH. Blood hematocrit and urine pH were not affected by treament. Magnesium oxide increased fecal pH .8 units and slightly decreased fecal starch, but sodium bicarbonate had no effect.