Calcium and Phosphorus Balances of Milking Cows Under Varying Conditions

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Abstract
The calcium and phosphorus balance trials with milking cows, upon which this paper is based, were started by the writer and his associates at the Vermont Experiment Station in 1924 and have been continued intermittently ever since. Nearly one hundred of these trials have been completed and others are now being conducted. Lack of time prevents any review of the work of other investigators. But at that time (1924) statements were made that not only heavily milking cows but also most cows giving in excess of 10 pounds of milk per day, were usually in negative balance as regards these minerals; and further that these losses, particularly of calcium, could not be prevented by feeding mineral supplements. Also it was claimed that usually 80 percent or more of the calcuim contained in the feed was excreted in the feces. The senior author was chairman of the College Feed Conference Board, which first approved the addition of mineral supplements to ready mixed dairy rations in the East. He planned these trials to determine whether or not cows fed on normal rations typical of North Eastern farm conditions, were usually in negative calcium and phosphorus balance and whether or not they would make use of these added minerals. Most of the cows used were producing from l1/^ to 2 pounds of butterfat per day while on trial. Only a bare summary of results without details can be given here. Detailed reports are being prepared for publication by the Vermont Experiment Station.

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