Zoo Population Management
by | December 22nd, 2009

Andrea L. Goodnight, Associate Veterinarian Photo credit: Nancy Filippi

Open space is a prime commodity in almost any society. Who doesn’t like to “get away from it all” by finding a place where peace and quiet rule? At the Oakland Zoo, we strive to provide our animals with spacious enclosures, including areas that allow them to retreat from others. However, even with these spacious exhibits, there isn’t a lot of room for animal families to expand in size. Left unchecked, reproduction could result in overcrowded and unhealthy exhibit environments, decrease genetic diversity, and prevent natural social or family groups from living together. The bottom line is that there’s just not enough room in captivity for all of those animals.

In order to prevent such overpopulation, the Association of Zoos and Aquariums (AZA) formed a Wildlife Contraception Center in 1989. Based on the recommendations of reproductive physiologists, veterinarians, and animal husbandry experts, this group advises AZA institutions on the best ways, with minimal risk and discomfort for the animals, to prevent overpopulation in their collections. As an AZA accredited facility, the Oakland Zoo benefits from this expertise.

How do we accomplish contraception at the Zoo? Among the many possibilities are oral medications, including feed additives, liquids, or pills that animals consume daily. Some animals are given implants of contraceptives that may last for several years. Many hoofstock receive a vaccination that prevents the female’s eggs from being fertile. All of these methods are reversible, in case future breeding may be warranted. Surgical methods of contraception are also available. We consider these when permanent contraception is necessary or when disease is present in the reproductive organs.

Here are some examples of contraception in place at the Oakland Zoo: all non-breeding female giraffes receive liquid melengestrol acetate daily in a food treat and all non-breeding female chimpanzees receive a daily pill combination of norethindrone and estradiol (a human medication). Both male lions had vasectomies when they were younger. This technique was chosen in order to keep their hormones and male characteristics, including their manes, intact.

Zoo animals are not the only ones at risk of overpopulation. According to the American Veterinary Medical Association, millions of unwanted dogs and cats are euthanized each year because there are not enough homes for them. You can make a difference. Surgical contraception, by spay or neuter, not only helps decrease the pet population, but it also benefits each individual animal. When pets are spayed or neutered early in life, aggressive or unwanted behavior due to hormone cycles may be eliminated and the incidence of several types of reproductive cancers almost disappears.

Working together, AZA institutions strive to prevent overpopulation and maintain genetic diversity throughout the animal kingdom. The Oakland Zoo is proud to support the mission of promoting a natural balance of animal and human populations.

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