Dietary vitamin A modulates the concentrations of RRR-alpha-tocopherol in plasma lipoproteins from calves fed milk replacer

The practice of supplementing milk replacers fed to neonatal calves with hi gh 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 exp eriment 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 m u mol daily as retinyl acetate] and two forms of vitamin E (RRR-alpha-tocop herol and RRR-alpha-tocopheryl acetate, 155 mu mol daily) on plasma RRR-alp ha-tocopherol and RRR-gamma-tocopherol and RRR-alpha-tocopherol associated with plasma lipoproteins (Lp) from milk replacer-fed Holstein calves from b irth to 28 d of age. The VLDL, LDL, HDL and very high-density lipoprotein ( VHDL) fractions were separated by ultracentrifugal flotation, and the amoun t of vitamin E associated with each fraction was determined by normal-phase HPLC. The amount and distribution of RRR-alpha-tocopherol in Lp fractions were unaffected by the form of dietary vitamin E. Plasma and Lp RRR-alpha-t ocopherol concentrations increased with age (P < 0.0001) and were maximal a t 28 d of age. Concentrations of RRR-alpha-tocopherol associated with Lp we re 25% (P < 0.01) to 39% (P < 0.0001) lower in calves fed 35.6 and 71.2 mu mol of vitamin A daily than in control carves at 28 d of age. The RRR-gamma -tocopherol concentrations were unaffected by dietary vitamin A (P greater than or equal to 0.05). In conclusion, dietary vitamin A modulated the amou nt and distribution of RRR-a-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-alpha-tocopherol concentrations in carves fed vitamin A at 35.6 and 71 .2 mu mol need to be investigated.