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Zoo Biol. 2011 Sep-Oct;30(5):550-65. doi: 10.1002/zoo.20375. Epub 2011 Jan 18.

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

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Veterinary Department, San Francisco Zoological Gardens, One Zoo Road, San Francisco, California 94132, USA.


The goals of this study were to have an improved understanding of milk composition and to help create a suitable milk formula for cubs raised in captivity. Milk samples were evaluated for fat, fatty acids, carbohydrate, vitamin D(3), 25(OH)D(3), vitamin A (retinol), vitamin E (α-tocopherol), protein, and amino acids. Total lipids in milk did not differ for cubs (mean ± SEM = 26.60 ± 1.88 g/100 ml vs. yearlings 27.80 ± 2.20 g/100 ml). Milk lipids were of 23.6% saturated fatty acid for cubs and 22.4% for yearlings. Milk consumed by cubs and yearlings contained 43.8 and 42.0% mono-unsaturated fatty acids and 23.4 and 21.9% polyunsaturated fatty acids, respectively. Carbohydrate content was higher in milk for cubs (4.60 ± 0.64 g/100 ml) than for yearlings (2.60 ± 0.40 g/100 ml). Vitamin D(3) concentration of milk was 18.40 ± 5.00 ng/ml in early lactation compared with 7.60 ± 2.00 ng/ml for mid-lactation. 25(OH)D(3) was lower in milk consumed by cubs (162.00 ± 6.70 pg/ml) than in milk consumed by yearlings (205.00 ± 45.70 pg/ml). Vitamin A concentrations were 0.06 ± 0.01 and 0.03 ± 0.01 µg/ml for cubs and yearlings, respectively. Vitamin E was higher in milk consumed by cubs (20.16 ± 4.46 µg/ml) than by yearlings (7.30 ± 1.50 µg/ml). Protein content did not differ in milk available to cubs (11.40 ± 0.80 g/100 ml compared with milk for yearlings 11.80 ± 0.40 g/100 ml). Taurine was the most abundant free amino acid at 3,165.90 ± 192.90 nmol/ml (0.04% as fed basis).

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