Abstracts Health Sciences

Study of immune response and uptake of lipid-soluble vitamins by dairy cattle

by Burim Namik Ametaj

min A, D and E are lipid-soluble nutrients essential for many physiologic and immune functions. Effects of active metabolites of vitamin A and D, retinoic acids (RA) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D 3), respectively, are mediated by their nuclear receptors. Because of the well-known roles of these vitamins, they are fed to periparturient cows and neonatal calves at levels that exceed NRC requirements by several fold. There are concerns that feeding greater than the NRC requirements of these vitamins might have deleterious effects on their uptake and on the functional capacity of the immune system. The objective of the first two studies was to evaluate the in vitro effects of 1,25(OH)2D3, two synthetic analogues of vitamin D, and all-trans-, 9-cis-, 13-cis-, and 9,13-dicis-RA on interferon-gamma (IFN-gamma) secretion by mononuclear leukocytes (MNL) from postparturient cows and nulliparous heifers. We showed that 1,25(OH)2D3 and its fluorinated analog (Delta22-26-F3-1,25(OH)2 D3) inhibited IFN-gamma secretion. Our results showed that individual RA isomers had no effect on IFN-gamma secretion whereas combinations of all-trans-RA with 9-cis-, 13-cis-, or 9,13-dicis-RA and of 9-cis-RA with 13-cis- or 9,13-dicis-RA as well as 1,25(OH)2D3 with 9-cis-RA inhibited IFN-gamma secretion. These results and those indicating 1,25(OH)2D3 and RA potentiate IgM production by bovine MNL, suggest that these vitamins may selectively promote differentiation of bovine T-cell subsets toward a Th2-like phenotype. In the third study, we evaluated feeding 20- to 40-fold the NRC requirements of vitamin A and two forms of vitamin E (alcohol and acetate ester) on the uptake of vitamin E by plasma lipoproteins in newborn calves. Our results showed that feeding greater than the NRC requirement of vitamin A decreases concentrations of vitamin E in plasma lipoproteins. Because of the critical antioxidant role of vitamin E, the health-related consequences associated with depression of lipoprotein vitamin E must be investigated. The form of vitamin E had no effect on concentrations of vitamin E associated with plasma lipoproteins suggesting the more stable and less costly RRR-alpha-tocopheryl acetate be used as a dietary supplement in calves.