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Article

Dietary Vitamin A Modulates the Concentrations of RRR--tocopherol in Plasma Lipoproteins from Calves Fed Milk Replacer ^{1 ,2 ,3}

Burim N. Ametaj^*, Brian J. Nonnecke⁴, Sharon T. Franklin^**,5, Ronald L. Horst, Wayne R. Bidlack, Robert L. Stuart and Donald C. Beitz^*

^* Department of Animal Science, Iowa State University, Ames, IA 50011; National Animal Disease Center, Agricultural Research Service-U.S. Department of Agriculture, Ames, IA 50010; ^** Department of Dairy Science, South Dakota State University, Brookings, SD 57007; Department of Human Food Nutrition, California State University, College of Agriculture, Pomona, CA 91768; and Stuart Products, Inc., Bedford, TX 76022

⁴To whom correspondence should be addressed.

The practice of supplementing milk replacers fed to neonatal calves with high concentrations of vitamin A has raised concerns regarding the effect of excess vitamin A on the bioavailability of vitamin E. A 4 x 2 factorial experiment evaluated the effects of four dietary amounts of vitamin A [0, 1.78 [National Research Council (NRC)⁶ requirement, control], 35.6 and 71.2 µmol daily as retinyl acetate] and two forms of vitamin E (RRR--tocopherol and RRR--tocopheryl acetate, 155 µmol daily) on plasma RRR--tocopherol and RRR--tocopherol and RRR--tocopherol associated with plasma lipoproteins (Lp) from milk replacer-fed Holstein calves from birth to 28 d of age. The VLDL, LDL, HDL and very high-density lipoprotein (VHDL) fractions were separated by ultracentrifugal flotation, and the amount of vitamin E associated with each fraction was determined by normal-phase HPLC. The amount and distribution of RRR--tocopherol in Lp fractions were unaffected by the form of dietary vitamin E. Plasma and Lp RRR--tocopherol concentrations increased with age (P < 0.0001) and were maximal at 28 d of age. Concentrations of RRR--tocopherol associated with Lp were 25% (P < 0.01) to 39% (P < 0.0001) lower in calves fed 35.6 and 71.2 µmol of vitamin A daily than in control calves at 28 d of age. The RRR--tocopherol concentrations were unaffected by dietary vitamin A (P 0.05). In conclusion, dietary vitamin A modulated the amount and distribution of RRR--tocopherol in the circulation of milk replacer-fed neonatal calves. Because of the essential antioxidant role of vitamin E, the health-related consequences associated with the depression of the LP RRR--tocopherol concentrations in calves fed vitamin A at 35.6 and 71.2 µmol need to be investigated.

KEY WORDS: • calves • vitamin A • vitamin E • lipoprotein • milk replacer