Effect of Varying Dietary Ratio of Sodium and Chloride on the Responses of Lactating Dairy Cows in Hot Weather

Twenty-four lactating Holstein and Jersey cows were fed concentrate mixtures formulated to supplement total diets with 1) no added sodium chloride, 2) 1.0% sodium chloride, 3) 1.14% calcium chloride, and 4) 1.45% sodium bicarbonate during a 9-wk continuous trial, Experiment 1. Responses measured were body temperature, respiration rate, milk yield, milk composition, and 15 blood variables to evaluate acid-base status and express metabolic profile. Treatments affected body temperature and pH, bicarbonate, total carbon dioxide, and base excess of blood. No treatment affected milk yield and composition. Differences in dietary electrolytes had little influence on responses. In a second experiment immediately following the first, a 1-km walking stress was imposed during midafternoon on 3 days; treatment did not influence change in response variables or recovery from stress although Jerseys recovered faster than Holsteins.