Effect of Ration on Free Choice Consumption of Calcium-Phosphorus Supplements by Dairy Cattle

Abstract

Daily individual consumption of dicalcium phosphate by 69 lactating Holstein cows was measured for 22 consecutive weeks in a continuous feeding trial. The four rations fed did not differ significantly in their influence on the amount of free choice mineral consumed. Individual variation in mineral consumption was large in all four ration groups. The correlation between free choice consumption of dicalcium-phosphate and the requirement for calcium and phosphorus was small though significantly different from zero,Three rations of greatly different calcium content were offered ad libitum to three groups of 15 yearling dairy heifers each in a 3×3 Latin square design with six-week periods. Each pen was offered a dicalcium phosphate (pH 3.5) and a defluorinated phosphate (pH 8.5). Type of ration had no significant effect on the total amount of supplement eaten. Dicalcium phosphate was preferred to defluorinated phosphate under all ration regimes. There appeared to be little relationship between consumption of the supplements and the need for calcium and phosphorus. There was no indication of an attempt by the heifers to narrow a wide calcium to phosphate ratio by selection of an appropriate mineral supplement or to widen a very narrow ratio by the same means.When dairy cows and heifers were fed rations which provided calcium and phosphorus in excess of requirements, luxury consumption occurred when simple calcium-phosphorus supplements were offered free choice.