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

I. Calcium, Phosphorus, and Vitamin D^{1, 2,}

Animal and Dairy Science Department, University of Vermont, Burlington

ABSTRACT

Before attempting to reevaluate the recommended level of feeding of any nutrient or group of nutrients, it is extremely important to appreciate the complexity of the factors in our present recommendations and to determine if there have been significant changes on our feeding practices.

Experiments with a number of animal species have shown that efficiency of utilization of both calcium and phosphorus is reduced as the ratio is significantly changed from the generally recommended range of 1:1. However, there seems to be a tremendous species difference in an animal's ability to withstand this deviation. Bohstedt (1) noted with swine that when the ratio of calcium to phosphorus exceeded 1.5:1, the rate and economy of gain progressively declined. But the ruminant animal appears to be more resistant to vide calcium-to-phosphorus ration; exactly to what extent appears to be somewhat controversial. In general, work with ruminants other than dairy cows has indicated that ratios as high as 5:1 (3), 6.5:1 (6), and 10.5:1 (5) can be tolerated without any visible detrimental effect. The trials with the exceptionally wide ratios were conducted in the early 1930's.

¹ University of Vermont Agricultural Experiment Station Journal Article no. 153.

² This research was supported by Eastern States Farmers Exchange.