Effect of dietary calcium and stage of lactation on potassium balance in lactating Holstein cows through 20 weeks of lactation

Potassium balance in dairy cows has been related to lactation performance and metabolic response to heat stress. Potassium balance was evaluated in 18 lactating Holsteins, 10 primiparous and 8 multiparous, during wk 2, 5, 8, 11, and 20 of lactation using 4-d total collection trials. Cows were fed diets containing 0.52, 0.78, and 1.03% Ca from calving. Dry matter and K intake increased as lactation progressed, but cows were in negative K balance in early lactation, with a nadir at wk 2. Urinary excretion was the primary route of K excretion, and proportion of K excreted via urine was affected by dietary Ca (greatest with 0.78% Ca) and parity (greater in first lactation cows). Parity had no effect on K balance. As Ca concentration in the diet increased, the amount of K in feces decreased, suggesting increased apparent K absorption.