title: Plasma vitamin A levels in cattle in response to large doses of vitamin A.
abstract: A dose response procedure was developed for evaluating vitamin A status and utilization in cattle. This could be useful for evaluating diets, vitamin A stores and homeostatic control of vitamin A. Three experiments were designed to determine: 1) size of vitamin A dose required to increase plasma vitamin A concentrations; 2) time after dosing when plasma vitamin A concentrations peak, and 3) if changes in plasma vitamin A concentrations are useful in assessing dietary vitamin A utilization. Using twenty-four steers and heifers, the first two experiments showed that 30X or 40X daily vitamin A requirement (daily requirement calculated as X = body weight in kilograms times 55 International Units of vitamin A) given orally was sufficient to cause plasma vitamin A concentrations to rise 20 hours after dosing. Plasma vitamin A concentrations increased (P less than .01) from 57 to 81 micrograms/dl and 64 to 84 micrograms/dl after a 30X or 40X treatment, respectively. Twenty-X daily requirement resulted in a slight increase after 20 hours (P greater than .05). Seventy-two feedlot steers were used in experiment three to determine if diet affects vitamin A dose response. Variations in feed intake, monensin in the diet or a single dose of vitamin E did not cause significant changes in plasma vitamin A response to vitamin A dosage. Steers receiving monensin had higher initial plasma vitamin A concentrations, but no differences were observed after dosing. Results indicate that dose responses may be useful in assessing dietary vitamin A utilization.
authors.affiliation: Department of Animal Science, University of Kentucky, Lexington 40546.
authors.forename: M L
authors.initials: ML
authors.lastname: Westendorf
authors.forename: G E
authors.initials: GE
authors.lastname: Mitchell
authors.forename: N
authors.initials: N
authors.lastname: Gay
authors.forename: R E
authors.initials: RE
authors.lastname: Tucker
authors.forename: N
authors.initials: N
authors.lastname: Bradley
mesh_terms: D000284:Administration, Oral; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D009752:Nutritional Status; D014801:Vitamin A / Q000008:administration & dosage / Q000097:blood*
chemical_list: D014801:Vitamin A