Lisa M. Mazzaro; J. Lawrence Dunn; Harold C. Furr; Richard M. Clark
University of Connecticut, Storrs, CT; Mystic Marinelife Aquarium,
Most institutions in the United States supplement the diets of their pinnipeds with a number of vitamins including vitamin A. The amount of vitamin A supplementation varies greatly. Before guidelines for vitamin A supplementation can be made more must be learned about the absorption and metabolism of vitamin A in pinnipeds. This study investigated the effect of vitamin A supplementation (10,000 IU compared to 50,000 IU/day) on plasma kinetics of vitamin A in northern fur seals. Didehydroretinol (vitamin A2) is a naturally occurring, biologically active form of vitamin A that has been used to assess vitamin A status in rats and humans. In this study two adult female northern fur seals were given an oral dose of vitamin A2 (100 ug/kg body weight) before and after a one month period of high vitamin A supplementation. Blood samples were drawn over a 5 day period after ingestion of vitamin A2. Plasma was analyzed for vitamin A1 and A2 by high performance liquid chromatography. The time of apparent maximum absorption, mean sojourn time (MST), and disposal rate (DR) were determined for vitamin A2 analog.
High vitamin A supplementation had no effect on the amount of time vitamin A spends in the body before irreversible utilization (MST). There was also no apparent effect on DR with vitamin A supplementation, suggesting that excess vitamin A is being stored in the liver. The animals in this study had a vitamin A requirement, based on DR, which ranged from 300 to 600 IU/day. For most other mammals, the vitamin A dietary requirements range from 1500 to 4000 IU/kg dry diet (NRC, 1987). In conclusion, it appears that supplementing with 10,000 IU vitamin A per day is adequate and that there is no justification for supplementation with greater amounts of vitamin A.