Normal Variations in the Inorganic Phosphorus of the Blood of Dairy Cattle

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Abstract
The inorganic phosphate of the blood has been studied ex- tensively in recent years because of its relation to various prob- lems of nutrition, metabolism, and disease. In cattle the effect of the phosphorus level of the food on the percentage of inorganic phosphorus of the blood has already been demonstrated by us (1) (2). During the collection of these data we were impressed by the fact that unaccountable, and frequently large fluctuations may occur from day to day. This result led us to adopt the mean of the blood phosphate values obtained on three consecutive days as the probable true value. The day-to-day fluctuations, however, remained unexplained. The physiological factors influencing the concentration of blood phosphate have not been studied extensively. Havard andRcay (3) seem to have been the only workers who have noted marked periodic fluctuations. They report that the concentration of blood phosphate is very unsteady in human blood studied at hourly intervals when the subject is not kept completely at rest. Ordinary movements of the subject about the laboratory cause large variations. Havard and Reay believe that these changes are the result of exercise which they later (4) showed causes first a small rise and then a rapid fall in blood phosphate. In these studies the lowest level was reached hour after the period of exercise. working with rabbits, observed
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