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The Mineral Metabolism of the Beef Steer

(From the Institute of Animal Nutrition, Pennsylvania State College, State College, Pa.)

A series of 10 nutritive balances of the calcium, magnesium, phosphorus, and nitrogen of normal feeds at four planes of nutrition, with each of two two-year-old steers, was determined in experimental periods mostly 18 days in length.

The planes of nutrition studied were, (a) half of the energy-maintenance requirement, (b) maintenance, or energy equilibrium, (c) half more than maintenance, and (d) twice maintenance.

A ration of corn (maize) meal and alfalfa hay, in equal weights, was fed at each of the four planes of nutrition; and in addition a ration of alfalfa hay alone was fed at the energy-maintenance level, with each steer.

The mineral metabolism of the steers was found to be of the normal character for growing animals, and not to be characterized by the peculiarities of the mineral metabolism of the milk-producing cow.

The balance data signify that with the mixed ration of corn meal and alfalfa hay, at planes of twice maintenance, half more than maintenance, and maintenance, the intake of calcium, magnesium, phosphorus, and nitrogen was adequate; that at the plane of half of the energy-maintenance requirement the intake of magnesium was adequate, of calcium was at about the point of equilibrium, and of phosphorus and nitrogen was definitely insufficient; while with the ration of alfalfa hay alone at the maintenance level the intake of all elements studied was adequate.

Eighteen-day balances of mineral elements such as calcium and phosphorus, which are utilized to the extent of considerable proportions of the usual intake of the same, are of value as indicating the adequacy of the quantities present to serve the nutritive requirements of the animal, though a continuous series of such balances would yield more reliable data; but balances of mineral nutrients such as magnesium, which are utilized in small proportions of the usual intake, are of much less certain significance, and cannot be closely interpreted—especially in view of the great complication of factors, other than the quantity present, which enter into the determination of the balance of intake to outgo.