Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/1999
Publication Date: N/A
Citation: Interpretive Summary: Newborn calves are born with minimal reserves of vitamins A and E because the transfer of these vitamins from the pregnant cow to the fetus is limited. Both vitamins have been shown to be essential in assuring normal growth and optimal function of the immune system. Natural deficiencies of these vitamins at birth are overcome by feeding colostrum within hours after birth, but for management reasons dairy-breed calves are frequently separated at birth from the dam and placed on a diet consisting of milk replacer. Because commercially available milk replacers contain vitamin A at levels exceeding current recommendations of the National Research Council (NRC) by greater than 20-fold and previous research has suggested that dietary vitamin A may influence absorption of other nutrients, the present study evaluated the effects of dietary vitamin A (from 0 to 68,000 International Units [IU]/day) on the amount of vitamin E in the circulation nof Holstein calves fed milk replacer. When compared to vitamin E concentrations in calves receiving vitamin A at the NRC recommended level (1700 IU/day) for large-breed calves, vitamin E concentrations in the circulation of calves given excess vitamin A (greater than or equal to 34,000 IU/day) were substantially reduced. The amount of vitamin E associated with the lipoprotein fractions of the blood of calves given excess vitamin A was also substantially reduced when compared to calves given recommended levels of vitamin A. Because vitamin E is an essential antioxidant and free radical scavenger in the body, these results raise concerns regarding the widely accepted practice of supplementing commercial milk replacers fed to newborn calves with escess vitamin A. These results will greatly benefit the dairy producers and industry.
Technical Abstract: 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 4 dietary amounts of vitamin A [0, 1.78 (NRC requirement, control), 35.6 and 71.2 micromole daily as retinyl acetate] and 2 forms of vitamin E (RRR-alpha-tocopherol and RRR-alpha-tocopherol acetate (155 micromole daily) on plasma RRR-alpha-tocopherol and RRR-gamma-tocopherol and RRR-alpha-tocopherol associated with plasma lipoproteins from milk replacer-fed Holstein calves from birth to 28 d of age. The VLDL, LDL, HDL and VHDL fractions were separated by ultracentrifugal flotation, and the amount of vitamin E associated with each fraction was determined. The amount and distribution of RRR-alpha-tocopherol in lipoprotein fractions were unaffected by the form of dietary vitamin E. Plasma and lipoprotein RRR-alpha-tocopherol concentrations increased with age and were maximal at 28 d of age. Concentrations of RRR-alpha-tocopherol associated with lipoproteins were 25-39% lower in calves fed 35.6 and 71.2 micromole of vitamin A daily than in control calves at 14 and 28 d of age. RRR-gamma-Tocopherol concentrations were unaffected by dietary vitamin A. In conclusion, dietary vitamin A modulated the amount and distribution of RRR-alpha-tocopherol in the blood 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 lipoprotein RRR-alpha-tocopherol concentrations in calves fed vitamin A at 35.6 and 71.2 micromoles daily need to be investigated.