The Calcium and Phosphorus Metabolism of Heavily Milking Cows

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Abstract
The experiments reported in this paper are part of a mineral feeding project instituted for the purpose of studying the effects of different calcium and phosphorus levels and different mineral supplements on the growth, health, reproduction and milk pro- duction of dairy cattle from six months to five years of age. ~ The investigations of Forbes and his associates (1) indicated that the calcium and usually the phosphorus balances were negative when milk production exceeded 10 pounds per day. Losses of these elements occurred with liberally milking cows regardless of the supply in the ration. Similar results were reported by Hart, Steenboek, Hoppert, Bethke, and Humphrey (2), Meigs, Blather° wick, and Cary (3), and Meigs, Turner, Harding, and Hartman (4). However, Hart, Steenbock, Hoppert and Humphrey (5) stated that they were able to maintain heavily producing cows in positive calcium balance by feeding alfalfa hay cured under caps, and to reduce losses of calcium and phosphorus in cows receiving timothy by the addition of bone meal. Hart and his associates (6) also maintained positive calcium balances by the addition of marl. Miller and his associates (7) reported increased calcium reten- tion after supplementing the basal ration with bone meal. At the Vermont Agricultural Experiment Station (8) positive calcium and phosphorus balances were maintained when bone meal and limestone rock were added to the ration of liberally milking cows. Perkins and Monroe (9) secured positive calcium balances with liberally milking cows on a narrow ration. Our own experience indicated that (a) cows could usually be
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