Birth control drug has health repercussions for zoo animals.
Isis the lioness arrived at Chicago’s Brookfield Zoo six years ago with a job: give birth. Brookfield hadn’t seen lion cubs in decades.
The zoo carefully planned her courtship with its new male, Zenda. Keepers took Isis off birth control. The community was excited. But nothing happened.
And it wasn’t just at Brookfield. The lioness Asali, at Ohio’s Columbus Zoo, wasn’t getting pregnant either. Nor was Kiki in Atlanta or Neka in Oregon. At the same time, scientists at the St Louis Zoo were coming to a startling conclusion: dozens of lionesses, including Isis, had been on birth control – but the drug wasn’t wearing off. The implants, meant to last six months to a year, were still in effect three, four, even five years later.
Now US researchers are trying to figure out the extent of the problem, the impact on zoo breeding programmes – and whether some of these animals will ever bear offspring again.
The Wildlife Contraception Centre, an arm of the Association of Zoos and Aquariums housed at the St Louis Zoo, is the distributor of Suprelorin, the drug used on the lionesses, to accredited zoos in North America. The centre has recorded more than 3,300 treatments for about 1,600 exotic animals, from polar bears to monkeys to meerkats.
But it has documented only 88 animals that have “reversed” – gotten pregnant or produced sperm – in nearly a decade of treatments. Of the 200-plus species treated, the centre has seen reversals in just 50. Not one of the six or seven polar bears given Suprelorin, species experts said, has had cubs. It’s far too early to draw permanent conclusions, researchers say. Many of the zoos caring for those animals have not yet tried to breed them. Still, the zoo community is unsettled.
“I think we also should use a lot more caution when we make the decision to place an animal on contraception,” said Budhan Pukazhenthi, a reproductive physiologist at the Smithsonian Conservation Biology Institute at the National Zoo in Washington who works with lions.
Spokesmen for Virbac Corp, the US subsidiary of a French pharmaceutical group that makes Suprelorin, haven’t returned multiple e-mails and phone calls on this subject.
The issue is key to the future of North American zoos. Still transitioning from the years of cages and pits, zoos now often say they exist for two primary reasons: to educate the public on wildlife conservation, and to provide a backup plan should species die out. To accomplish the first goal, leaders prefer to exhibit animals in wild settings – herds of elephants, bands of gorillas, prides of lions. But to achieve the second, and for the ongoing health of their animals, they need to carefully watch those family groups, and only allow breeding between individuals of the right genetics, at the right time.
The alternative, zoo leaders note, is to kill unwanted animals, as do some European zoos. Recently, the Copenhagen Zoo in Denmark shot a two-year-old male giraffe with a bolt gun, dismembered it in public and fed the remains to its lions – despite an online protest petition with thousands of signatures.
Contraception, Copenhagen Zoo officials noted, has health repercussions.
At last fall’s Association of Zoos and Aquariums conference in Kansas City, contraception centre leaders called a special session on the topic to plead for data from the continent’s zookeepers. They have some numbers: 118 lionesses had been treated with Suprelorin, said Hollie Colahan, large mammal curator at the Denver Zoo and coordinator of the association’s lion species survival plan. Only nine had documented reversals.
Like most US zoos, Brookfield has long had lions. They are popular animals and draw crowds. They also weren’t really a priority 30 years ago, said Bill Zeigler, Brookfield’s senior vice president of collections and animal care. Zoos have limited space, and give priority to endangered animals. Lions weren’t endangered. Tens of thousands roamed the plains and savannas in Africa.
Then they started dying in the wild by the thousands. Some were killed by diseases like canine distemper, a virus that ravaged jackals, foxes and dogs. But far more died by spear, trap and poison as their territory collided with human expansion, and African farmers and herders protected their land and livestock, according to Luke Hunter, president of the wild cat conservation group Panthera.
Suddenly zoos were more interested in telling the story of lions, Zeigler said. Brookfield, however, didn’t have a female. And the zoo couldn’t decide on its own to find and breed lions. Zoo leaders, through the Association of Zoos and Aquariums, had created formal programmes to keep zoo populations of endangered species full of animals of different ages and genetics. Those programmes, called species survival plans, dictated who would breed, and when. It was years before Brookfield got tapped.
Finally, in 2008, the association’s lion team sent the zoo Isis, age two, from the Fort Worth Zoo, and Zenda, also two, from San Diego’s Wild Animal Park. They introduced the cats slowly. Sex between wild animals isn’t a sterile event. “Lion mating involves teeth and claws and a little bit of blood,” said Denver’s Colahan. When things don’t work out, animals can die.
So Brookfield first put Isis and Zenda in nearby pens; they could see and likely smell each other, but couldn’t touch. They progressed to an exhibit with a steel mesh – called a “howdy” gate – separating the lions. After four months, keepers lifted the gate.
The zoo association, however, didn’t immediately give Brookfield the green light to breed. Lions are assigned a number that designates their genetic worth. Isis and Zenda weren’t the most genetically valuable at that moment, so the association team didn’t move them to the front of the line. Besides, Isis was still a little young. So, in 2009, Brookfield put Isis on one dose of Suprelorin.
The drug was a godsend at first. From 1975 until the early 2000s, keepers used the drug melengestrol acetate, or MGA. But as the years of treatment mounted, zoos were discovering lionesses with diseased reproductive tracts. Sometimes the cats died. In 2002, a group of scientists published a paper after studying preserved tissue from more than 200 wild cats. MGA, they found, was tied to uterine overgrowth, lesions, sterility and, sometimes, cancer. At that point, zoos basically stopped using MGA. And for a few years, leaders didn’t know what to do. Most simply didn’t implant their lions with any contraceptives.
Then Cheryl Asa, director of the contraception centre and of research at the St Louis Zoo, stumbled onto Suprelorin, developed in Australia for domestic dogs by a company called PepTech Animal Health, later purchased by Virbac. It was – and still is – unapproved for use in the United States. But Asa helped swing a deal with the US Food and Drug Administration (FDA): the contraception centre would import the drug for investigational use and centre staffers would carefully track all treatments.
An FDA spokeswoman declined to comment, saying federal regulations bar the department from even acknowledging the existence of such a study. But the zoo community embraced it. Early studies – some by PepTech itself – indicated Suprelorin was safe, effective and promised to be reversible. For several years, all went well.
Emerging side effects
Keepers were perhaps the first to realise something was wrong. In 2009, Zoo Atlanta had seven lions: four adults and three new cubs. “We had a lot of lions to manage,” said Rebecca Snyder, the zoo’s curator of mammals. Atlanta put Kiki, its new mum, on one dose of Suprelorin. (It could have put Kiki’s mate, Kamau, on the contraceptive. But Suprelorin makes male lions lose their manes, something no one likes.) A year later, however, Kiki wasn’t coming back into heat. Atlanta began to wonder if she would ever get pregnant again.
In 2012, the zoo association’s Population Management Centre analysed the status of zoo lions. In general, the study found, things were fine. Still, it warned, “If the females on contraceptive do not breed again, the population will experience a much more severe decline.”
No matter how this ends, some zoo staffers say they’ll be more cautious going forward.
“I think it was sort of recommended across the board without really knowing what the long-term consequences were going to be,” said Zoo Atlanta’s Snyder. “I think we all learned a lesson from that.”
The call for data from other zoos, Asa hopes, will help flesh out the issues. Still, Asa and her team have already learned some things. The implant breaks up under the animal’s skin. If veterinarians can remove it first, animals reverse more quickly. And some animals, for no particular reason, seem to be recovering on their own. Neka, in Oregon, had three cubs in September. Kiki had four in November.
Others are still waiting. It’s now been three or four years since the Columbus Zoo gave lionesses Asali and Kazi their last dose, and they still aren’t pregnant.
But Brookfield’s still hopeful. Isis showed signs of going into heat last fall, Zeigler said. Zenda seemed interested. But, still, no success.
“This is why we brought this pair in,” Zeigler said. “And it’s sort of been a waiting game ever since.” — St. Louis Post-Dispatch/McClatchy Tribune Information Services