Effect of the plane of nutrition on the ash constituents of cow's milk
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Only within the last few years has the importance of the mineral elements of food been recognized. The mineral elements are especially necessary during the period of growth, for, while they form but a very small part of the food, serious results occur when they are not present in sufficient quantity. Calcium and phosphorous are needed for the building up of bony structure. Rickets is sometimes caused by an insufficient supply of these in the food. A condition resembling rickets in children was produced in puppies by feeding them only lean and fat meat, while other puppies, from the same litter developed normally with the same food and, in addition, bones to gnaw. Phosphorous is needed for the central nervous system and iron in the hemoglobin of the blood. Since the mineral elements are so necessary in the food during growth, the ash constituents of cow's milk, which forms such an important part of the diet of infants, is of considerable importance in connection with the use of milk as food. One thing that might effect the mineral content of the milk, is the plane of nutrition of the cows. It is quite certain that all commercially kept dairy cows are at some periods underfed and at others overfed. It is possible that in the same herd and at the same time some cows may be underfed and others overfed. In times of drought when pasturage is poor or there is a shortage in the food supply, it is possible that the cows furnishing the milk for an entire city may be underfed. Just what effect the diet has on the mineral constituents of milk we do not know. It was with the hope of contributing something to the knowledge of milk as a food that the present investigation was undertaken.