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Effects of Dietary Vitamin D₃ on Concentrations of Vitamin D and Its Metabolites in Blood Plasma and Milk of Dairy Cows¹

Nutritional Physiology Group, Department of Animal Science, Iowa State University, Ames 50011

E. Travis Littledike and Ronald L. Horst

National Animal Disease Center, Agricultural Research Service, US Department of Agriculture, Ames, IA 50010

ABSTRACT

To determine the effect of supplemental dietary vitamin D₃ on concentration of vitamin D and its metabolites in milk, 20 Holstein cows were assigned to four groups and fed either 0, 10,000, 50,000, or 250,000 IU of vitamin D₃/d beginning approximately 2 wk prepartum and continuing through wk 12 of lactation. Samples of blood plasma and milk were assayed for concentrations of vitamin D, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and 24,25-dihydroxyvitamin D. Only the daily dosage of 250,000 IU caused significant increases of concentrations of vitamin D or 25-hydroxyvitamin D in plasma. Concentrations of vitamin D and 25-hydroxyvitamin D in milk were approximately equal and averaged .2 ng/ml. Little 1,25-dihydroxyvitamin D and no 24,25-dihydroxyvitamin D could be detected in milk from any of the four treatment groups. Cows fed 250,000 IU of vitamin D₃/d produced milk containing 54 IU of vitamin D activity per liter, whereas unsupplemented cows produced milk containing 17 IU/L. Oral supplementation with up to 250,000 IU of vitamin D₃/d does not increase effectively vitamin D activity of milk.

¹ Journal Paper No. J-11504 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project 2393.

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