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Symposium: Re-Evaluation of Nutrient Allowances for High-Producing Cows

II. Calcium, Phosphorus, and Vitamin D¹

Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster

ABSTRACT

In the re-evaluation of the calcium, phosphorus, and vitamin D requirements of high-producing cows, it may he helpful to consider the complexity of the factors that influence dietary needs under different conditions. The decrease with increasing age in the ability of the cow to absorb calcium from the feed and to mobilize stored calcium, plus increased endogenous excretion with advancing age (5), suggests that the age of the cow needs to be taken into consideration in estimating her needs.

More information is needed on the limitations imposed on milk production, especially in high producers, by insufficient calcium or phosphorus intake. Under these conditions the apparent adaptive ability of the cow to conserve calcium, the efficiency of the parathyroids in regulating blood calcium, the extent and availability of the stored calcium, and perhaps the amount of vitamin D in the feed may all be important factors in determining the amount of calcium and phosphorus available for milk synthesis.

¹ Published with the approval of the Associate Director of the Ohio Agricultural Research and Development Center as Journal Article no. 61–65.