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Effects of Varying Amounts of Calcium and Phosphorus in Rations for Dairy Cows¹

Department of Animal Sciences and Industry
and Department of Veterinary Medicine and Surgery, Oklahoma State University, Stillwater 74074

ABSTRACT

Different dietary percentages and ratios of calcium and phosphorus were studied with 48 dairy cows in a randomized block design. The respective members of each block were assigned to one of three ration treatments: a) Ca: P ratio approximately 3:1, 0.4% phosphorus; b) Ca:P 3:1, 0.6% phosphorus; and c) Ca:P 1.5:1, 0.6% phosphorus. Response criteria were blood mineral concentrations, milk yield and composition, parturient paresis, and reproductive performance. Average blood serum inorganic phosphorus was lower (P < .05) in the cows fed the 0.4% phosphorus ration than in the other treatment groups at all times, except on the day of calving. Blood serum calcium was highest in the group fed the 0.4% phosphorus ration. No differences in blood serum magnesium, potassium, copper and zinc, or in milk production and composition were attributed to the ration treatments. In the lowest phosphorus group (.4% P), incidence of ovarian dysfunctions was higher, and in addition, a larger number of services per conception were required in the second breeding season.

¹ Journal Article 2106 of the Agricultural Experiment Station, Oklahoma State University, Stillwater. This research was supported in part by Farmland Industries, Inc., Kansas City, Missouri.

² Taken from a thesis presented to the Graduate College, Oklahoma State University, by the senior author in partial fulfillment of the requirements for the M.S. degree.

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