Every day about the same time, Missy gets a pill that’s popped out of a 28-day blister pack similar to the ones that millions of women take to keep from getting pregnant. But Missy isn’t like most females on a birth control prescription. She’s a chimp.

Because chimpanzees share a similar anatomy to humans, they can take the same pill in much the same way as a woman does. But because they are animals, Dallas Zoo keepers sometimes have to come up with ways to disguise it.

Missy prefers to take her pill diluted in brightly colored juice, but Koko, who is no longer on birth control, would take hers only when it was mixed into oatmeal or served from a favorite pirate cup.

"They're smart," said Tami Jochem, assistant supervisor of primates at the Dallas Zoo. "Everyone has their own little idiosyncrasies that we cater to, of course."

There are a number of reasons why zoos use birth control — breeding recommendations, space constraints, health concerns — but it's all done under the careful watch of keepers looking out for side effects and ensuring that social structures are maintained.

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Human-like options

Like the pill Missy takes because keepers aren’t sure if the 52-year-old chimp is in a menopause-like state, many of the contraceptive options used at the Dallas Zoo are widely familiar to humans — oral, shots or implants.

“There’s not really a market for wild animal contraceptives, so we do adapt products that are approved for humans,” said Dr. David Powell, director of the Association of Zoos and Aquariums Reproductive Management Center at the St. Louis Zoo. “But there’s never going to be enough tigers or capybaras for any drug company to go through the millions of dollars to develop a specific contraception for Asian small-clawed otters.”

But researchers did develop Suprelorin, an implant that costs $30 to $60 and was originally created for ferrets because the pet trade is full of them.

With an implant, keepers don't have to worry about whether or not the animals are actually taking a contraceptive.

“The biggest problem we have with oral contraception in animals is poor compliance: They spit their pills out, or they don’t eat enough of the feed or something like that,” said Dr. Christopher Bonar, Dallas Zoo director of animal health.

With the exception of Missy's pills and a shot primates can get, most of the animals on birth control have implants or injectable formulations prepared by veterinarians that differ from what is used in humans, Bonar said.

There’s also hysterectomy or castration, an irreversible way to avoid long-term hormone therapy.

Bonar has performed vasectomies on both a rattlesnake and a lion.

His previous zoo decided to perform the procedure on the lion to keep the animal from impregnating its sister. Castration would have kept him from growing a mane, and the zoo wanted to keep the female off hormonal birth control because of its side effects.

Strictly animal options

There are options that humans can’t really relate to.

For snakes or birds, keepers can replace an egg with a decoy or choose not to incubate.

Immunocontraception, originally developed for feral horses, works by tricking the female's body into creating antibodies against its own egg so the animal doesn't become pregnant, Powell said.

The Dallas Zoo employs the method for its naked mole rat.

The animal is also capable of a kind of contraception that requires no human intervention.

A queen naked mole rat suppresses the ability for all other females in the group to cycle or reproduce. As soon as the queen dies, there’s a fight to take her place, Powell said.

Contraceptive measures can have side effects on animals, including an increased risk of cancer and difficulty becoming pregnant later.

“Sometimes altering their hormonal cycles alters their behavior and position in the social structure,” Bonar said.

Experts are also researching the physical effects of taking away the ability to breed.

Deborah Chase, vet tech, left, holds a helmeted guineafowl as Dr. Chris Bonar, director of animal health at the Dallas Zoo, injected a solid birth control implant into Zotz, Pez and Skittle on Aug. 31, 2017. (David Woo / Staff Photographer)

Birth of animal contraception

The idea of developing contraception for zoo animals dates to the 1970s, when zoos realized there was not enough space to hold all the new offspring, Bonar said.

Around that time, biologists also started to learn the negative effects of inbreeding and zoos adopted a more thoughtful process that eventually led to the creation of the Species Survival Plan.

The plan, which manages 500 animal populations and is overseen by the Association of Zoos and Aquariums, plays matchmaker for animals at accredited zoos across the country.

When deciding where to place animals, studbook keepers and species coordinators consider the overall population of animals in human care and weigh the needs of different institutions: Does a zoo have space to take in a giraffe? Could it use a companion for an animal or another tiger for public display?

Breeding recommendations are made to prevent inbreeding and ensure good genes don't pass out of the population.

That’s where the Reproductive Management Center comes in. The center gathers and provides data to zoos about contraceptive use, efficacy, reversibility and safety to help keepers make decisions about how to help animals breed or not.

Part of that work is expanding research into how to promote reproduction for struggling species, such as cranes, and to ensure zoo populations are sustainable, Powell said.

According to plan

Beyond space constraints and genetic concerns, there are social implications to weigh before putting an animal on birth control.

A zoo with only female gorillas may feel it needs a male for the troop’s social hierarchy. But if not all the animals have been recommended for breeding, contraception is necessary, Bonar said.

It may also be required for animals that have already reproduced many times and spread their genes throughout the population.

Zoos also factor in weather.

When Boipelo arrived in Dallas in March, the hippopotamus, a notoriously fertile breed, was put on birth control to prevent her from delivering a baby in the winter.

Like in humans, hormonal measures aren’t always 100 percent effective.

Boipelo’s mate, Adhama, was transferred to Dallas from the Los Angeles Zoo because a female hippo there became pregnant despite being on birth control, said Harrison Edell, the Dallas Zoo's vice president of animal operations.

Though staff — and guests — get excited when an animal has a baby, zoos try to ensure all births are planned.

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“These are not babies we use to support the budget; the babies are produced to be part of carefully managed program,” Edell said, citing the Species Survival Plan.

When Lina gave birth in March through C-section to the zoo's first lion cub in 43 years, it was after years of weighing with the Species Survival Plan's lion coordinator at the Denver Zoo the pros and cons of breeding a lion who previously had two stillborns.

"It’s real easy to take a pot shot and say we created a cute baby lion because we wanted to boost attendance,” Edell said. “Do people come up to the zoo to see a baby lion? Of course, she’s pretty damn cute. ... But there’s so much more to it than that."

Birth control at the Dallas Zoo

Source: The Dallas Zoo