Colo was the first gorilla in the world born in a zoo and has surpassed the usual life expectancy of captive gorillas by two decades.
"Colo just epitomizes the advances that zoos have made, going all the way back to her birth at Columbus," said Dr. Tom Meehan, vice president for veterinary services at Chicago's Brookfield Zoo and veterinary adviser to a national gorilla species survival plan.
Today, zoo veterinarians regularly treat animals for heart and kidney disease, arthritis, dental problems and cancer.
Hundreds of people gathered at the zoo Thursday to see Colo, singing "Happy Birthday" moments before the gorilla ambled into an enclosure decorated with multicolored construction paper chains and filled with cakes such as squash and beet and cornbread with mashed potato parsley frosting.
At Seattle's Woodland Park Zoo, staff members use acupuncture, massage, laser therapy, and heat and joint supplements to help Emma, a 13-year-old rabbit.
At the National Zoo in Washington, Shanthi, a 42-year-old Asian elephant with arthritis, receives osteoarthritis therapy and was recently fitted with specially crafted front foot boots to help her feet heal as medications are applied.
"Geriatrics is probably one of our most common medical challenges that we face in a zoo situation," said Dr. Keith Hinshaw, director of animal health at the Philadelphia Zoo.
Coldilocks, a 36-year-old polar bear at the Philadelphia Zoo and considered the oldest polar bear in the U.S. The bears' typical lifespan in captivity is 23 years.
The zoo says treating her early for kidney disease appears to have helped prolong her life.