Influences of Calcium Intake and Vitamin D Supplementation on the Composition of Lactating Cows’ Blood

Abstract

Two rations with Ca:P ratios averaging 1.1 :1 and 2.3 :1, each with and without 300,000 IU supplemental vitamin D3 weekly by capsule, were fed to study the effects on concentrations of calcium and several phosphorus fractions in blood of 46 Holstein cows, each for 1 to 3 lactations. High energy rations (alfalfa hay-sorghum grain-soybean oil meal), supplemented to furnish more than adequate phosphorus with calcium in the indicated ratios, were group fed to satiety. During the first year, following only 45-day pretrial treatment, serum calcium, inorganic phosphorus and magnesium were not influenced significantly by imposed treatments. During two succeeding years, preceded by at least 5-month pretreatment for all cows, plasma calcium was greater in blood from cows fed the lower calcium ration (432 observations). Vitamin D supplementation did not influence measured blood constituents but interacted with Ca :P ratios so the larger packed cell volume and greater phosphorus content of blood cells were associated with vitamin D supplement in the narrow Ca:P treatment and with no vitamin D supplement in the wider Ca :P treatment. Plasma phosphorus and plasma inorganic phosphorus were not influenced significantly by treatment. All measures, except blood cell phosphorus concentrations in cells and in blood, varied significantly with stage of lactation. © 1971, American Dairy Science Association. All rights reserved.