Polarbears International

Could the lack of a key amino acid contribute to bone disease in captive polar bear cubs? Thanks to funding from PBI and other sources, a team of researchers from the San Francisco Zoo and LeBonheur Children's Medical Center is investigating this question.

The problem of bone frailty was well-publicized in 1994 when the Denver Zoo bottle-fed two polar bear cubs, Klondike and Snow, after they were abandoned by their mother. Both cubs developed rickets, leading zoo veterinarian David Kenny to give them an injection of Vitamin D and modify their diet. Kenny later analyzed serum from wild polar bears and discovered that it contained large amounts of Vitamin D. New research shows that taurine, an amino acid, may play an important role in allowing that vitamin to be absorbed.

"Studies have shown that taurine-free formulas in infants have led to Vitamin D deficiencies with nutritional rickets," says lead researcher Gail Hedberg, RVT, of the San Francisco Zoo. "Captive white Bengal tigers and leopards have also had problems due to lack of taurine, as have domestic and barnyard cats."

These findings--and the presence of rickets and poor bone density in captive polar bear cubs--led Hedberg and her co-researchers, Freeland Dunker, DVM, of the San Francisco Zoo and Russell Chesney, MD, of LeBonheur Children's Medical Center at the University of Tennessee, Memphis, to examine whether a lack of taurine could lead to metabolic bone disease in captive polar bears.

The team's objective is to examine blood and maternal milk samples from both captive and free ranging polar bears. In addition to testing for taurine, the team will look at each sample's Vitamin D levels. Preliminary work done with samples from the San Diego Zoo, San Francisco Zoo, Detroit Zoo, and Sea World San Diego show that taurine levels in both plasma and whole blood are sixty percent lower in captive polar bears than in four-month-old wild cubs.

In conducting their study, the team will rely on blood and milk samples from a wider group of North American zoos. These will be compared with samples from wild bears provided by Dr. Andrew Derocher of the Canadian Wildlife Service (formerly with the Norwegian Polar Institute) and Dr. Robert J. Letcher of the Great Lakes Institute for Environmental Research, University of Windsor, Ontario, Canada. In addition, the team will benefit from guidance provided by Dr. Quinton Rogers, professor of Nutrition and Veterinary Sciences at the University of California, Davis.

Findings from this research will help zoos further understand the importance of taurine in zoo carnivore diets.

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