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.

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