Responses of Holstein calves to dietary calcium, phosphorus, and vitamin D3 using response surface techniques

The metabolism of calcium, phosphorus, and vitamin D has been a classical topic of nutrition studies through the past fifty years. Many experiments have been conducted to determine the relationship of calcium, phosphorus, and vitamin D in the animal body. All results have led to the conclusion that vitamin D will affect the absorption and/or retention of calcium and phosphorus, and the amount of calcium will affect calcium and phosphorus metabolism. However, the effect of the dietary level of phosphorus has been questioned (1, 56, 65, 69). The chemistry and site of the majority of these actions is still to a great extent unknown.

The usual procedure for studying a problem of this type is to hold two of the factors constant and vary the third. Information obtained from studies of this type is limited in that it relates to only one set of conditions. A mathematical description of responses as related to any dietary combination within limits of calcium, phosphorus, and vitamin D would be desirable.

The primary objective of this study was to quantitatively relate calcium, phosphorus, and vitamin D over a comparatively wide range of each and to determine the dietary combinations for maximum absorption, retention, and growth in the dairy calf. A secondary objective was to check the validity of mathematical techniques in describing biological systems.