Twenty-four lactating cows were assigned randomly to three treatments to evaluate responses to large differences of dietary sodium and chloride. Treatments were corn-cottonseed meal-corn silage based complete rations with either: 1) .23% sodium chloride (control), 2) control plus 2.28% calcium chloride, or 3) control plus 1.70% sodium bicarbonate. Treatment effects were significant for urine pH (7.96, 5.41, 8.18), blood pH (7.50, 7.39, 7.49), partial pressure of oxygen (91.2, 99.4, 86.3 mm Hg), partial pressure of carbon dioxide (34.60, 30.57, 32.98 mm Hg), bicarbonate (26.20, 18.06, 24.64 meq/liter), total carbon dioxide (27.51, 19.18, 25.88 mM/liter), base excess (4.50, -4.31, 3.13 meq/liter), plasma chloride (93.4, 102.8, 95.7 meq/liter), serum potassium (3.26, 4.24, 4.14 meq/liter), and inorganic phosphorus (7.11, 5.61, 6.80 mg/100 ml). Blood glucose (45.1, 43.0, 55.5 mg/dl) and blood urea nitrogen (11.8, 8.7, 11.9 mg/dl) exhibited treatment effects. Respiration rates, 84.8, 61.8, 89.9 per min, and body temperatures, 39.7, 39.0, and 40.0 degrees C were significantly different. Lower intake of the high chloride diet and higher intake of the bicarbonate diet were probably responsible for some of the effects. Dietary electrolytes should receive attention in formulation because acid-base status of the animal is determined, in part, by ionic concentration and balance of the diet.

Twelve Holstein and eight Jersey cows in the first half of lactation were assigned to one of four concentrate formulations to provide supplemental sodium salts in the total diet dry matter of 1) .5% sodium chloride, 2) .5% sodium chloride plus .72% sodium bicarbonate, 3) .5% sodium chloride plus .72% sodium bicarbonate, and 4) 1.44% sodium bicarbonate to measure effects on body temperature and respiration rate, milk yield and composition, and blood components that reflect acid-base balance. After data were adjusted for body weight, age, and a covariate based on differences within individuals in the standardization period, they were analyzed with a model that included breed, treatment, week, temperature-humidity index, and interactions. Cow fed sodium bicarbonate and no supplemental sodium chloride had lower body temperatures than the other groups. High sodium and chloride in basal diet and drinking water prevented the large change in dietary amount and ratio of these two electrolytes that treatments were designed to impose. More stringent control of dietary amounts and greater heat stress will be necessary to show effects of these elements on acid-base balance.