Effect of Dietary Calcium and Sodium on Potassium Requirement for Lactating Dairy Cows

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Abstract
The effect of dietary Ca and Na on the K allowance of 0.7-0.8% for lactating cows was studied. First-lactation cows (12) in midlactation were fed 3 diets containing 0.52, 0.77 and 1.04% K with 4 dietary Ca concentrations 0.50, 0.69, 0.87 and 1.03%. Increasing dietary K from 0.52-1.04 increased intake of dry feed as a function of body wt. With rations containing 17% coarsely ground fiber, increasing dietary Ca up to 1.03% increased intake and milk production 1.3 kg/day and 1.6 kg/day linearly. Cows (16) in midlactation were fed rations with 2 K (0.42 and 0.84%) and with 2 Na concentrations (0.31 and 0.52%). Increasing dietary K increased dry matter intake 1.2 kg/day. Dietary Na had no effect on intake. K had no effect, but increasing Na decreased fat-corrected milk 1.7 kg/day. Of K, Na, Mg and Ca in serum, K was the element most consistently affected. Increasing dietary K to 0.77 and 0.84% increased serum K. Dietary Ca and Na had little effect on K required for lactating cows.