Determination of vitamins D, A, and E in sera and vitamin D in milk from captive and free-ranging polar bears (Ursus maritimus), and 7-dehydrocholesterol levels in skin from captive polar bears

Abstract

The difference between serum levels from 36 captive and 56 free‐ranging polar bears (Ursus maritimus) for 25‐hydroxyvitamin D (25‐OH‐D) was found not to be significant (mean ± SD = 348 ± 215 nmol/L [captive], 360 ± 135 nmol/L [free‐ranging], t = 0.30, df = 52.8, P = 0.76), whereas the difference for retinol and α‐tocopherol was significant (retinol, 1.37 ± 0.67 μmol/L [captive] 1.89 ± 0.63 μmol/L [free‐ranging], t = 3.88, df = 72.4, P <0.001, α‐tocopherol, 18.56 ± 18.56 μmol/L [captive], 48.76 ± 13.92 μmol/L [free‐ranging], t = 7.85, df = 61.9, P < 0.001). Due to the high fat content in the polar bear diet, seal blubber may be the source of these fat‐soluble vitamins. Six skin biopsies were analyzed from captive polar bears at the Denver Zoological Gardens for 7‐dehydrocholesterol levels and found to contain 0.11 ± 0.03 nmol/cm2. This finding also helps to support the contention that the source of vitamin D for polar bears may be ingestion and not cutaneous production. Vitamin D content in the milk from one captive sow in the den (0.14 nmol/g) and 10 free‐ranging sows with cubs of the year out on the ice pack (0.0042 ± 0.0073 nmol/g) were also evaluated. It would be helpful to evaluate additional milk samples from denning and non‐denning sows with cubs to see whether vitamin D content varies according to the stage of lactation. Zoo Biol 17:285–293, 1998. © 1998 Wiley‐ Liss, Inc.

Growth and development of Polar bearUrsus maritimuscubs at Denver Zoological Gardens

“…The disadvantage of black skin is that it acts like sun block and inhibits the epidermal production of vitamin D 3 (Holick, 1994). Polar bear skin has about 10% of the ability to produce this vitamin when compared to human skin (Holick, 1992;Kenny et al, 1998). Ongoing research at the Denver Zoological Gardens indicates that Polar bears may be satisfying their vitamin D 3 requirements primarily through ingestion and not through cutaneous production.…”

Physiological limit of the daily endogenous cholecalciferol synthesis from UV light in cattle

“…In humans, pigs and cattle, UV light is a significant source of endogenous D 3 (Horst and Littledike, ; Webb et al., ), whereas species evolved and living in habitats lacking in, or void of, sunlight obtain vitamin D solely from dietary sources as either D 2 or D 3 . For example, polar bears have very low capacity for D 3 synthesis in the skin, probably due to adaptation to heavy fur coverage at far northern latitudes and a marine diet high in D 3 (Kenny et al., ) and in mole rats, which live under ground, plasma concentrations of 25OHD 3 can only be increased through oral supplementation with D 3 and not by exposure to UV light (Pitcher et al., ), probably because their natural vitamin D source is D 2 from moulds in their diet. Isolated skin from fur‐covered animals such as rats, rabbits and guinea pigs can synthesise D 3 (Bekemeier, ), and the plasma concentration of 25OHD 3 in rats does increase during UV‐light exposure (Lawson et al., ) but it has been speculated that D 3 in rat skin is synthesised in the sebum on the fur and subsequently ingested by the rat during grooming (Carpenter and Zhao, ).…”

Milk composition in free‐ranging polar bears (Ursus maritimus) as a model for captive rearing milk formula

“…Previous data for milk composition of polar bears in studies by Baker et al [1963], Cook et al [1970], and Jenness et al [1972] utilized 10 samples collected during lactation (7–29 months). New data emerged evaluating early and mid‐lactation samples as described by Derocher et al [1993a] and Kenny et al [1998] with a much larger sample pool >100 and all five references were used to design hand‐rearing formulas for polar bear cubs in captivity [Hedberg, 2002; Slifka and Jacobson, 2005].…”

“…Five of the last 20 hand‐reared polar bear cubs less than 3 months of age developed metabolic bone disease that was linked to nutrient deficiencies [Hedberg et al, 2009]. In 1994, these deficiencies were corrected in two hand‐reared cubs at the Denver Zoo, Denver, CO by supplementing the milk formula with cod liver oil [Kenny et al, 1999] as a source for increasing fat [Hedberg, 2002] and especially the long‐chain omega‐3 FA and vitamin D [Kenny et al, 1998].…”

“…The study of Derocher et al [1993a] provides reasonably complete information on the composition of polar bear milk for total solids, total protein, total lipids, ash, carbohydrates, and gross energy. However, limited data are available for Vitamin D 3 [Kenny et al, 1998] and there is also a lack of information on the other fat‐soluble vitamins including vitamin A (retinol) and vitamin E (α‐tocopherol). Similarly, there are no published data on the complete fatty acid and free amino acid composition of polar bear milk.…”