Dietary Vitamin A Modulates the Concentrations of RRR-α-tocopherol in Plasma Lipoproteins from Calves Fed Milk Replacer

摘要

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 × 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-α-tocopherol and RRR-α-tocopheryl acetate, 155 μmol daily) on plasma RRR-α-tocopherol and RRR-γ-tocopherol and RRR-α-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-α-tocopherol in Lp fractions were unaffected by the form of dietary vitamin E. Plasma and Lp RRR-α-tocopherol concentrations increased with age (P 0.0001) and were maximal at 28 d of age. Concentrations of RRR-α-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-γ-tocopherol concentrations were unaffected by dietary vitamin A (P ≥ 0.05). In conclusion, dietary vitamin A modulated the amount and distribution of RRR-α-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-α-tocopherol concentrations in calves fed vitamin A at 35.6 and 71.2 μmol need to be investigated.