Response of dairy cows to sodium bicarbonate and limestone in early lactation.

A total of 108 dairy cows at three locations were fed a diet supplemented with sodium bicarbonate and limestone during the first 16 wk of lactation. Complete mixed diets were fed for ad libitum intake and consisted of concentrate and corn silage (60:40, dry matter). The four treatments were: 1) basal diet, 2) basal plus 1.2% sodium bicarbonate, 3) basal plus 1.4% limestone, and 4) basal plus 1.2% sodium bicarbonate plus 1.4% limestone. Dry matter intake was increased for 8 wk by sodium bicarbonate, then decreased from wk 9 to 16. Intake was decreased by limestone alone or in combination with sodium bicarbonate. Sodium bicarbonate increased milk production for 8 wk and 4% fat-corrected milk for 16 wk. Average dry matter intake, milk production, and 4% fat-corrected milk (kg/day) for the 16 wk were: 1) 20.2, 31.1, 27.3; 2) 19.8, 32.0, 28.7; 3) 18.9, 31.4, 27.9, and 4) 18.4, 29.7, 27.2 for diets 1 to 4. Ruminal pH was decreased, and volatile fatty acid concentration was increased by added sodium bicarbonate and appeared to result from increased feed intake. Digestibility of nutrients was unaffected by supplements. Sodium bicarbonate affected regulation of blood and urine pH and concentration of electrolytes more than limestone. Serum magnesium was reduced with sodium bicarbonate, although not beyond normal physiological reference range.