The Mineral Metabolism of the Milch Cow

This investigation was suggested by the phenomenal mineral content of milk, and by observations on the behavior of milch cows which raised a question as to whether the mineral metabolism might not become a matter of critical importance in conditions of nutritional stress, especially as resulting from extreme develop ment of the lactating function through selective breeding.These observations were the following: (1) There is greater difficulty in getting a cow with calf after heavy and prolonged lactation than if bred comparatively soon after calving; (2) cows bred too young tend strongly to remain permanently small; (3) occasionally a cow will fail, unaccountably, after calving, to approach her normal milk production; (4) cows calving while in especially thin condition, or calving without having had an adequate dry, resting period, are apt to begin lactation at less than the normal rate, or, after a brief term of production, to fail abruptly; and (5) performance tests of milch cows, under conditions of forced production, have resulted in the loss of breeding capacity of so many superior cows as to occasion frequent comment and discussion among dairy cattle breeders.That these unfavorable conditions have resulted from nutritive depletion seems unmistakable.To determine the importance of mineral metabolism in this relation was the primary object of this study, the method being to ascertain through a series of income and outgo experiments the role of the several mineral elements, and also nitrogen, in the annual cycle of lactation and gestation.