Vitamin A repletion in thoroughbred mares with retinyl palmitate or beta-carotene.
Forty-five Thoroughbred mares used in an 8-mo depletion study were kept for an additional 20 mo on the same three forage diets (15 mares each): 2-yr-old orchardgrass hay and vitamin A-free concentrate on a drylot (HC); pasture, orchardgrass/alfalfa hay, and vitamin A-free concentrate (PHC); or pasture and orchardgrass/alfalfa hay only (PH). Each diet group was divided into three subgroups, and mares (n = 5) in each group were given either retinyl palmitate (A) at twice the NRC (1989) recommended daily intake, the equivalent amount of vitamin A in the form of water-dispersible beta-carotene (B), or the vehicle (C). Vitamin A status was monitored with serum retinol and a relative dose response (RDR) test every 60 d. In the C subgroups, retinol concentration was 18.65 +/- .84 micrograms/dL (mean +/- SE) and the RDR was 16.26 +/- 1.72% over the 20 mo. Retinol and RDR fluctuated seasonally regardless of supplementation. Vitamin A status, based on serum retinol (P = .001) and RDR (P < .001) values, was lower in the HC than in the PH and PHC. Vitamin A status, based on retinol (P = .05) and RDR (P = .013) values, was improved by retinyl palmitate supplementation in all diet groups, but not by water-dispersible beta-carotene supplementation. Supplementation of the HC mares with vitamin A matched the serum retinol, but not the RDR, of the two pasture, control subgroups. Thus, replete vitamin A status in previously depleted mares was barely obtained by supplementation with twice the currently recommended daily intake of vitamin A.
Greiwe-Crandell
K M
KM
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306, USA. kcrandel@ix.netcom.com
Kronfeld
D S
DS
Gay
L S
LS
Sklan
D
D
Tiegs
W
W
Harris
P A
PA
D000818:Animals; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D004224:Diterpenes; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses / Q000097:blood / Q000378:metabolism*; D000084562:Retinyl Esters; D012621:Seasons; D014801:Vitamin A / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D019207:beta Carotene / Q000008:administration & dosage / Q000494:pharmacology*
D004224:Diterpenes; D000084562:Retinyl Esters; D019207:beta Carotene; D014801:Vitamin A; C014794:retinol palmitate