The zoo is not unique. Some 223 accredited institutions are members of the Association of Zoos and Aquariums and ascribe to the Species Survival Plan, which was set to up to carefully monitor animal breeding to promote genetic diversity, The Cincinnati Enquirer reported Sunday.
"It is a very important part of what we do. It's being responsible," says Terri Roth, the zoo's vice president of conservation and science.
The Cincinnati Zoo has been so successful in its gorilla breeding program, it's had to put a halt on new births since 2006 to prevent its gorillas' bloodlines from being overrepresented in the North American population, the Enquirer said.
"We're a little bit of a victim of our own success," animal caretaker Ron Evans said. "No zoo is an island. We all have to cooperate to properly manage species."
Some animals, like the gorillas, are given crushed up birth control pills -- just like what humans use -- while others receive vaccines or implants. The zoo avoids more permanent, surgical neutering so the animals can possibly be bred again in the future.