In February, the Curious Case of Bridget’s Mane at the Oklahoma City Zoo became a global sensation with news organizations including CNN, Fox News, National Geographic, The Washington Post and Newsweek providing coverage. Global media from Canada, Russia, the United Kingdom, India and Japan also shared Bridget’s story with their audiences. On social media, the Zoo was inundated with notes of well-wishes, questions about potential medical conditions and requests for updates as soon as they became available.
Bridget, the OKC Zoo’s 18-year-old African lioness, sprouted a mini-mane between March and November of 2017. Her sister, Tia, also 18, remained mane-less. Veterinary staff and caretakers developed behavioral training methods that would allow them to safely draw blood from Bridget’s tail without the need for anesthesia. They successfully obtained a sample from Bridget and submitted it along with a banked serum sample from Tia serving as a baseline, or control sample, for comparison. These blood samples were sent to the veterinary school laboratory at the University of Tennessee for analysis. The results are in.
The Zoo’s veterinary team expected to find elevated testosterone hormone levels, since this hormone is most directly responsible for the production of manes in male lions. What they found was somewhat unexpected: Bridget and sister Tia had almost identical testosterone levels.
Bridget’s levels of two other hormones, cortisol and androstenedione, were notably elevated compared to Tia. Cortisol is a hormone produced in the adrenal glands, which is a small endocrine organ located near the kidneys. It functions to regulate most body systems including immune response and metabolism. Bridget’s cortisol levels were 7.1 mg/dl, compared to Tia’s 2.68 mg/dl, or about 2.5 times higher.
Androstenedione is produced in the adrenal and reproductive glands. It’s a pre-cursor to sex hormones like estrogen and testosterone and can contribute to the development certain androgenic (male) traits or features. Bridget’s androstenedione levels were 2.82 ng/ml, compared to Tia’s 0.41 ng/ml, or about 7 times higher.
These results most likely indicate a benign hormone-secreting tumor has developed in one of Bridget’s adrenal glands. Zoo veterinary staff report her overall health is excellent for an 18-year-old and, besides a little extra fur, the condition won’t affect her quality of life. Bridget’s mini-mane is not likely to continue to grow, but only time will tell.
A frequent concern raised online by fans of Bridget regarding her diet impacting her hormone levels was addressed by Zoo veterinary staff. They clarified that Bridget’s diet is strictly monitored and that she, and all carnivores at the OKC Zoo, are fed only USDA-inspected and approved meat. Click here to read more about USDA’s food safety and inspection service.
Going forward, Zoo veterinary staff and caretakers will continue to monitor Bridget's health with periodic blood level checks two to three times annually to check for changes that might indicate additional steps are necessary.
Photo credit: Amanda Sorenson, carnivores caretaker