The Calcium and Phosphorus Metabolism of Heavily Milking Cows

Abstract

Summary 1. A series of calcium and phosphorus balances on cows when in heavy, medium, or in low milk production and when dry, on a ration of timothy hay, corn silage, and grain indicates that the ration supplied sufficient calcium and phosphorus for the production of at least 10,000 pounds of milk a year. During the height of production the animals were frequently in negative balance but subsequently positive balances made up the loses. 2. Positive calcium and phosphorus balances were obtained in heavily milking cows when the above ration of timothy hay, corn silage and grain was supplemented with bone flour. A cow producing 80 pounds of milk a day showed positive calcium and phosphorus balances. 3. Positive calcium balances were obtained in heavily milking cows on a ration of alfalfa, silage and grain. 4. Cows fed a low calcium ration utilized calcium more efficiently than when the ration was high in this element. 5. There was a tendency for cows in heavy milk production to utilize both calcium and phosphorus more efficiently than when in low production or during the dry period. 6. The total intake of calcium or phosphorus has a greater significance in the utilization of these elements than has the Ca/P ratio in the food. We wish to thank Professor S. E. Crowe for assistance in the statistical treatment of the results.