The Curious Case of Contraceptives in U.S. Zoos

Some of the country’s captive animals are on birth control — and sometimes it works a little too well.

National Journal
Marina Koren
June 26, 2014, 1:10 a.m.

Each year, hun­dreds of an­im­als in European zoos are killed.

None of them are sick. Some are eu­th­an­ized in or­der to main­tain the num­ber of an­im­als a zoo is able to care for, oth­ers be­cause zoo­keep­ers do not find them suit­able for breed­ing. A gir­affe named Mari­us was killed this year for the lat­ter reas­on. The Copen­ha­gen Zoo, which eu­th­an­izes ap­prox­im­ately 25 healthy an­im­als every year, shot the gir­affe and then dis­membered it in front of vis­it­ors.

You won’t hear any­thing as gory or heart­less hap­pen­ing in the United States, though. That’s be­cause Amer­ic­an zoos prefer con­tra­cep­tion over eu­thanas­ia to curb pop­u­la­tions, pre­vent breed­ing, or pre­serve ge­net­ic qual­it­ies of a giv­en spe­cies. Creatures as big as lions and hip­pos and as small as meerkats and mice take birth con­trol — it’s crushed up in their feed, in­jec­ted in­to their veins, and im­planted un­der their skins.

The As­so­ci­ation of Zoos and Aquar­i­ums, the gov­ern­ing body of U.S. zoos, al­lows eu­thanas­ia, but it’s usu­ally re­served for ill or aging an­im­als. Plus, our an­im­al-lov­ing so­ci­ety can’t quite stom­ach the idea of put­ting down a zoo an­im­al for os­tens­ibly no reas­on, es­pe­cially chim­pan­zees and oth­er prim­ates, giv­en their sim­il­ar­it­ies to hu­mans.

“On an emo­tion­al level, I can’t ima­gine do­ing it and I can’t ima­gine our cul­ture ac­cept­ing it,” Cheryl Asa, the dir­ect­or of the Wild­life Con­tra­cep­tion Cen­ter, told Leslie Kauf­man of The New York Times in 2012, sug­gest­ing that con­tra­cep­tion is the bet­ter op­tion. “By pre­vent­ing the birth of an­im­als bey­ond car­ry­ing ca­pa­city, more an­im­als can be well cared for,” she said.

The Wild­life Con­tra­cep­tion Cen­ter, an arm of the As­so­ci­ation of Zoos and Aquar­i­ums, is the cap­it­al of exot­ic an­im­al con­tra­cep­tion in the U.S. Es­tab­lished in 1999, the St. Louis cen­ter provides in­form­a­tion about and mon­it­ors the use of con­tra­cep­tion for cap­tive wild­life in 200 Amer­ic­an zoos.

In the U.S., the ad­min­is­tra­tion of hor­mon­al birth con­trol in zoos began in the 1970s. Zoos were hav­ing trouble pre­vent­ing un­wanted preg­nan­cies and were selling or giv­ing away an­im­als they no longer had room for. The prac­tice co­in­cided with a grow­ing ac­cept­ance of birth con­trol use by hu­mans.

An­im­al birth con­trol comes in many forms: hor­mon­al treat­ments like pro­gestins, es­tro­gen, and pro­ges­ter­one; GnRH ag­on­ists, which sup­press the re­pro­duct­ive en­do­crine sys­tem; vac­cines, which cre­ate an­ti­bod­ies that block fer­til­iz­a­tion; and oth­ers.

Apes and mon­keys are the easi­est an­im­als to treat with con­tra­cept­ives, thanks to their bio­lo­gic­al re­semb­lance to hu­mans. They even ex­per­i­ence some of the same side ef­fects as wo­men on hor­mon­al birth con­trol, like weight gain. Car­ni­vores are the trick­i­est — the chem­ic­als that work on prim­ates ac­tu­ally stim­u­late car­ni­vores’ uter­uses, which can res­ult in tu­mor growth. Birth con­trol can also be ad­min­istered in male an­im­als, but zoos tend to avoid that prac­tice, es­pe­cially in lions. Some con­tra­cept­ive drugs cause lions to lose their bushy manes — and, by some ex­ten­sion, what makes vis­it­ors at­trac­ted to them.

But con­tra­cep­tion use in zoos has a dark side. Many drugs haven’t been com­mer­cially ap­proved by the Food and Drug Ad­min­is­tra­tion, yet they re­main in reg­u­lar use across the coun­try. The treat­ments are con­sidered “ex­per­i­ment­al,” and their use de­pends on ap­prov­al from the In­sti­tu­tion­al An­im­al Care and Use Com­mit­tee, which re­views pro­to­cols for an­im­al re­search. They must also be in com­pli­ance with the An­im­al Wel­fare Act, U.S. De­part­ment of Ag­ri­cul­ture-en­forced le­gis­la­tion that spells out an­im­al wel­fare reg­u­la­tions.

One of these ex­per­i­ment­al drugs — and one of the first ever to be used in zoos, in 1975 — Melengestrol acet­ate (MGA), led to neg­at­ive side ef­fects in cap­tive lions, in­clud­ing le­sions, ster­il­ity, and even death. In the early 2000s, it was re­placed by an­oth­er ex­per­i­ment­al con­tra­cept­ive called Suprelor­in, a GnRH ag­on­ist about the size of a grain of rice that is im­planted be­neath the an­im­al’s skin.

Suprelor­in re­mains in use today. It has also worked al­most too well, which has the zoo com­munity wor­ried. The slow-re­leas­ing hor­mones, meant to last six months to a year, were not wear­ing off sev­er­al years after the im­plants were re­moved from lions. “I think it was sort of re­com­men­ded across the board without really know­ing what the long-term con­sequences were go­ing to be,” Re­becca Snyder, the cur­at­or of mam­mals at Zoo At­lanta, told Dav­id Hunn of the St. Louis Post-Dis­patch in Feb­ru­ary. There, zoo­keep­ers are still wait­ing for a li­on­ess to get preg­nant after she stopped re­ceiv­ing birth con­trol. “I think we all learned a les­son from that.”

Ac­cord­ing to the Wild­life Con­tra­cep­tion Cen­ter, out of more than 200 spe­cies treated with Suprelor­in, only 50 have got­ten preg­nant or pro­duced sperm again after ceas­ing treat­ment — 88 an­im­als in total.

The use of con­tra­cept­ive drugs is a re­l­at­ively new ven­ture in the zoo busi­ness (and the hu­man busi­ness, too). Over the last few dec­ades, ex­perts have de­pended on tri­al and er­ror to find the right dosage based on an an­im­al’s age and be­ha­vi­or­al and so­cial factors. And they still can nev­er be sure how long it will take for an­im­als to re­gain their fer­til­ity once they’re off the med­ic­a­tion.

Re­search­ers say it’s far too early to draw con­clu­sions. Many zoos have not yet tried to breed an­im­als who were once ad­min­istered birth con­trol. But in the case of Suprelor­in and oth­er ex­per­i­ment­al drugs, the re­turn of fer­til­ity seems not to be guar­an­teed.

“I think we all should be wor­ried,” Bud­han Pukazhenthi, a re­pro­duct­ive physiolo­gist at the Smith­so­ni­an Na­tion­al Zoo’s Con­ser­va­tion Bio­logy In­sti­tute, told Hunn. “I think we also should use a lot more cau­tion when we make the de­cision to place an an­im­al on con­tra­cep­tion.”

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