title: Effects of supplemental vitamin A on retinoic acid concentrations in the plasma of preruminant calves.
abstract: Neonatal calves are fed frequently milk replacers with vitamin A concentrations exceeding those recommended by the National Research Council. The vitamin A metabolite, retinoic acid (RA), affects profoundly cellular differentiation and homeostasis. For this reason, effects of dietary vitamin A on plasma concentrations of RA isomers in milk replacer-fed calves were examined. Male, Holstein calves (n = 24) were fed colostrum within 12 hours after birth and, thereafter, a custom-formulated low vitamin A milk replacer providing 0, 1700 [National Research Council (NRC) daily requirement for young growing calves] (controls), 34,000 (industry standard in the United States) or 68,000 IU of vitamin A daily. Concentrations of retinol and RA isomers in plasma samples collected from birth to 27 days of age were determined by HPLC. Retinol was affected by dietary vitamin A with higher concentrations occurring in calves supplemented with > or = 34,000 IU of vitamin A/day than in control (1700 IU of vitamin daily) and unsupplemented calves. Relative to controls, concentrations of all isomers of RA were higher in calves supplemented with > or = 34,000 of vitamin A daily during the experimental period. The predominant isomer in all calves was 9,13-dicis-RA. In control calves, 9,13-dicis-RA and 9-cis-RA were maximal at 1 to 6 days of age and then decreased progressively. In calves fed > or = 34,000 IU of vitamin A daily, concentrations of these isomers were markedly higher at 6 days of age, relative to controls, and remained elevated for the duration of the study. In all calves, retinol was correlated positively with 9,13-dicis- and 9-cis-RA from 9 to 27 days of age. 9,13-cis-Retinoic acid was correlated positively with 9-cis- and 13-cis-RA from 13 to 27 days of age. It is concluded that supplementing milk replacer-fed calves with vitamin A at levels exceeding current NRC recommendations by > or = 20-fold causes an elevation in plasma concentrations of retinol and retinoic acids. 9,13-dicis- and 9-cis-Retinoic acids were most affected by supplemental vitamin A. Physiologic consequences of increased plasma RA concentrations induced by high dietary levels of vitamin A warrant investigation.
authors.affiliation: National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, 2300 Dayton Avenue, Ames, IA 50010, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Nonnecke
authors.forename: R L
authors.initials: RL
authors.lastname: Horst
authors.forename: D C
authors.initials: DC
authors.lastname: Hammell
authors.forename: S T
authors.initials: ST
authors.lastname: Franklin
mesh_terms: D000821:Animal Feed; D000818:Animals; D000831:Animals, Newborn / Q000097:blood* / Q000378:metabolism; D002417:Cattle / Q000097:blood* / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003126:Colostrum; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D007536:Isomerism; D008297:Male; D014212:Tretinoin / Q000097:blood*; D014801:Vitamin A / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*
chemical_list: D014801:Vitamin A; D014212:Tretinoin