Knoxville, TN (WOKI) Zoo Knoxville is mourning the loss of Dolly, a 56-year-old Southern white rhinoceros who called Zoo Knoxville home since 1976.

Zoo officials making the announcement Thursday say Dolly was euthanized humanely following a decline in her mobility.

Zoo Knoxville says that Dolly’s care team had been managing age-related conditions for some time, but in recent days, her mobility declined significantly despite ongoing medical support. After careful evaluation, the veterinary team, in collaboration with specialists from The University of Tennessee College of Veterinary Medicine, determined that there were no remaining treatment options that could maintain Dolly’s quality of life. With her well-being as the top priority, the difficult decision was made to humanely euthanize Dolly.

“This is an emotional time for everyone who has cared for and loved Dolly,” said Bill Street, President and CEO of Zoo Knoxville. “She was a remarkable animal, and her impact on this zoo and the people who have met her is immeasurable. Our priority was her comfort and dignity, and we take comfort in knowing she was surrounded by the people who knew her best.”

Born in the Hluhluwe-Imfolozi Park in South Africa, officials say Dolly was the oldest rhino in the United States and was one of the first white rhinos housed at Zoo Knoxville.

The zoo adds that Dolly was a very successful mother, raising 10 calves over her lifetime.