Modulation of fat-soluble vitamin concentrations and blood mononuclear leukocyte populations in milk replacer-fed calves by dietary vitamin A and beta-carotene

Dairy calves (n = 18), separated from dams at birth, were fed 1 L of pooled -colostrum. For the remaining 7 wk of the study, they were fed one of three diets consisting of either a custom-formulated milk replacer without vitam in A (controls), or supplemented with retinyl palmitate (equivalent to 32,0 00 IU of vitamin A/d) or with beta-carotene (equivalent to 20,000 IU of vit amin A/d). Plasma retinol, beta-carotene, and RRR-alpha-tocopherol concentr ations were lowest at birth, and increased substantially from birth to 1 wk postpartum in all groups, a probable consequence of ingestion of colostrum . From 1 to 7 wk of age, retinol concentrations were greatest in retinyl pa lmitate-supplemented calves, intermediate in beta-carotene-supplemented cal ves and lowest in control calves. At 2, 3, 5, 6, and 7 wk, RRR-alpha-tocoph erol concentrations were lower in retinyl palmitate-supplemented calves tha n in control calves. A negative correlation between plasma retinol and vita min E concentrations existed from wk 2 to 7, suggesting vitamin A influence s the absorption and distribution of RRR-alpha-tocopherol. Supplemental ret inyl palmitate, but not beta-carotene, was associated with a reduction in t he percentage of blood mononuclear leukocytes expressing CD2, CD4,and CD8 T cell antigens and interleukin-2 receptors. By wk 7, leukocyte populations from retinyl palmitate-supplemented calves were more similar to those from adult cattle than those from control calves, suggesting that supplemental v itamin A, as retinyl palmitate, affects the maturation of the neonatal immu ne system. Differences in the composition of blood mononuclear leukocyte po pulations may represent changes in immune competency.