title: Use of the relative dose response (RDR) assay to determine vitamin A status of calves at birth and four weeks of age.
abstract: An accurate assessment of vitamin A status can be determined by analysis of liver biopsy samples; however, liver biopsies are not always feasible. Plasma concentrations of vitamin A do not provide an accurate indication of vitamin A status. The objective of this study, therefore, was to determine the ability of the relative dose response assay to indicate the vitamin A status of Holstein calves. Calves were obtained at birth and assigned to vitamin A treatments (0, 1700, 34,000, or 68,000 IU/d) added to milk replacer. Liver biopsies and relative dose response assays were performed at birth and 4 wk. Calves supplemented with 1700, 34,000, or 68,000 IU of vitamin A/d had adequate (greater than 20 microg/g) liver concentrations of vitamin A at 4 wk of age. The relative dose response assay at 4 wk was correlated with liver concentrations of vitamin A. Both the relative dose response assay and liver concentrations of vitamin A indicated that calves not supplemented with vitamin A had low vitamin A status, whereas other treatment groups had adequate vitamin A status. Plasma concentrations of retinol increased by 4 wk of age in calves receiving supplemental vitamin A at 34,000 IU and 68,000 IU/d and decreased in unsupplemented calves; however, all calves had concentrations of <20 microg of retinol/dl of plasma. The relative dose response assay agreed with liver biopsies as an indication of vitamin A status, whereas plasma concentrations of retinol incorrectly indicated all treatment groups were deficient in vitamin A.
authors.affiliation: Dairy Science Department, South Dakota State University, Brookings 57007, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Hammell
authors.forename: S T
authors.initials: ST
authors.lastname: Franklin
authors.forename: B J
authors.initials: BJ
authors.lastname: Nonnecke
mesh_terms: D000821:Animal Feed; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D002417:Cattle / Q000378:metabolism*; D003126:Colostrum / Q000737:chemistry; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D008099:Liver / Q000737:chemistry*; D008297:Male; D009752:Nutritional Status; D011897:Random Allocation; D014801:Vitamin A / Q000008:administration & dosage / Q000032:analysis / Q000097:blood*
chemical_list: D014801:Vitamin A