Birth Control for Zoo Animals: Do the Benefits Outweigh the Risks?

If it weren’t for Margaret Sanger underwriting research to create the first birth control in 1950, animals wouldn’t be joining the contraception club as they’re doing today. Yes, the sexual revolution wouldn’t have happened in the 1960s, the Supreme Court wouldn’t have legalized birth control in 1972 for all citizens, married or not, and the Affordable Care Act wouldn’t have mandated that insurance companies provide “free birth control” for women in 2009; but most importantly, across America, there would be unnecessary spaying and castrating of endangered species in zoos to control the overpopulation of animals, and there’d be a lack of control over animals’ gene pools.  

Centuries ago, camel drivers going on long voyages across the Sahara put pebbles in camels’ uteruses to prevent pregnancy. In the 1970s, zookeepers resorted to more humane options when trying to control the reproduction of big cats. Zoo populations were once unmanaged and a high rate of births was usually followed by breeding inactivity. As a result, zoos would replenish their animals by capturing them from the wild. When that practice was no longer allowed in the 1970s due to the growing list of endangered species, sometimes inbreeding in zoos would occur, and newborn animals would be more susceptible to disease, infant death, and health abnormalities.

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Now, since 1981, as part of the Association of Zoos and Aquariums’ Species Survival Plan, 223 accredited institutions have been using birth control as part of their breeding plans for animals ranging from various primates and hoofed species like giraffes and deer, to geese. Primates like the bonobo, orangutan and six female gorillas at the Cincinnati Zoo and Botanical Garden, take human birth control pills, while the hoofed animals get a vaccine. The langur, lar gibbon, and siamang primates receive hormonal implants. After the successful births of forty-eight gorillas at the Cincinnati Zoo, breeding has been on hold since 2006 for fear that zoo's gorillas are overrepresented in the North American population. Primate team leader Ron Evans says of the Cincinnati Zoo’s previous breeding achievements, “We’re a little bit of a victim of our own success.”

Managing the contraception of zoo animals, however, proves to be highly lucrative for the animals’ health, gene diversity, and the longevity of the species’ existence. According to Terry Roth, Cincinnati Zoo’s Vice President of Conservation and Science, “It is a very important part of what we do.  It’s being responsible.”

Along with contraception, zoos must also be aware of its space constraints and the animals’ lineages so that if necessary, the animals can be moved to other zoos to diversify the gene pool.  Zoos can prevent breeding by separating the males from the females, but that would add to space constraints and prevent healthy social groups from forming.  

At St. Louis Zoo’s AZA Wildlife Contraception Center, birth control is not as simple as slipping a few pills to primates and calling it a day. According to the center’s director, Cheryl Asa, “Every time we're treating a new species, we are trying to figure out what's the right dose, how long it is going to be effective and what the reversal rate will be.”  

To Roth, in Cincinnati, birth control is still “experimental." After all, there are possible risks. For example, the hormonal steroids in human birth control can sometimes overstimulate the uteruses of carnivores and cause cancer. According to Seed Magazine, the AZA is researching a non-steroid animal birth control option, called deslorelin. The drug shuts down the endocrine reproductive system for up to a year in dogs and two years in lions. Asa’s research group administers it experimentally to a variety of species, but it’s currently approved for use only in Australia and New Zealand.

As for wild animal birth control, the most successful on the market, much to the chagrin of hunters, is the porcine zona pellucida vaccine, which is a pig protein that targets the membrane surrounding all mammal eggs and prevents sperm from entering. Although foolproof with wild deer, mustangs, koalas, elephants, brown bears, and kangaroos, PZP’s success rate for humans is variable and has thus not been put on the market.

As diverse birth control methods are tested among an increasing amount of animal species, wildlife groups remain divided on this issue. The Humane Society may endorse the PZP vaccine and OvoControl as non-lethal population control tools,  but the environmental group, Friends of Wetlands and Wildlife, has claimed that putting west Bengal elephants on birth control would be a “killing exercise.”  

Come this winter in Cincinnati, two female gorillas, Anju and Asha, will be purposely taken off the pill after they become acquainted with the family of the zoo’s 450-pound silverback, Jomo. After a gorilla breeding dry spell, this should be an exciting event for Cincinnati, and perhaps they’ll be able to reclaim their Newsweek Studio 54 status as having “the world’s sexiest zoo."

Allen Rutberg from the Center for Animals and Public Policy at Tufts Cummings School of Veterinary Medicine claims, “This (i.e. use of birth control) really crosses the boundary between human cultural activity and ‘the wild’. That is kind of the joke: The human influence on so-called wild populations is so pervasive that this is just another way in which people are attempting to influence wildlife.”  

Is it necessarily a bad thing that humans are influencing the health of wildlife in positive, productive ways, despite the possible shortcomings? Hasn’t this “one health” approach to birth control been effective? Tell us what you think in the COMMENTS below.

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Alessandra Rizzotti is the Associate Features Editor at Good Magazine and a writer for  She's been published in Smith, Heeb, and Neave's online magazines and currently runs the Los Angeles storytelling show, In Bloom: Stories About Growing Up, Still Growing, Or Never Growing Up At All.  Her corgie and three tuxedo cats are too cute for words.