Breeding Restraint at the Zoo

Watching the two female Masai giraffes at the Los Angeles Zoo, it is easy to imagine them loping across the savannas of their native Africa. Like their kin in the wild, the slender giants browse, chew their cud and rub their long necks together.

One is pregnant. The other is in a state unknown in nature: She is on birth control.

While the arrival of a baby elephant or panda is often a major media event, preventing unwanted pregnancies is also a key part of captive breeding programs today.

Because of better nutrition and healthcare, and more naturalistic exhibits that allow greater access to others of their species, zoo animals reproduce like never before and routinely live into old age. As a result, contraception has become crucial to keeping zoo populations from exploding.

“It’s a huge part of our job now,” said Cynthia Stringfield, senior veterinarian at the L.A. Zoo.

In some countries, surplus animals are put down. But because Americans won’t tolerate such treatment, most North American zoos practice a form of planned parenthood, aided by a growing pharmacopeia of birth-control agents and techniques.

During most of the 20th century, spaying and castrating were the standard ways to keep animals from reproducing. But zoos now avoid those practices whenever possible. Such surgeries permanently banish the individual from the breeding pool and can cause undesirable physical and behavioral changes.

Lions whose testes have been removed gain weight and lose their manes. Castrated elk develop weirdly shaped antlers. A chimp who has been neutered may have trouble bonding with his fellow males.

Separation of males and females keeps animals from breeding, but disrupts the normal relationships among social animals. By using the new contraceptive implant Deslorelin, the L.A. Zoo can keep its yellow-footed rock wallabies together, while preventing them from “breeding like bunnies,” Stringfield said.

While not foolproof, birth-control options for zoo animals have surged in the last decade, from sustained-release implants to a vaccine that makes eggs resistant to sperm.

But birth-control decisions remain complex. In addition to efficacy and safety, zoos must take into account reversibility, cost and possible impact on a fetus or nursing young, Stringfield said.

She regularly consults the website of the American Zoo and Aquarium Assn.’s Contraceptive Advisory Group, which for 15 years has collected data on a dozen contraceptives in nearly 300 species, from bats to dolphins.

The original animal birth-control device was probably the desert diaphragm devised centuries ago by Arabs who inserted small stones into the vaginal canals of camels. When the L.A. Zoo wanted to keep its camels from reproducing, it temporarily sterilized its male with the synthetic hormone Lupron. Used to treat human endometriosis, the drug would have cost $48,000 annually, had it not been donated by the manufacturer.

After consulting the association’s contraceptive website, Stringfield put a gorilla on human birth-control pills. The ape had been on an anti-fungal medication that could have caused birth defects, and the pill seemed like the safest option.

With endangered and rare animals, genetic concerns often drive contraception. The sex lives of all 50 Masai giraffes in North American zoos, including L.A.’s four, are managed by a Species Survival Plan, developed by a committee of the zoo and aquarium association.

A reproductive future has been worked out for each animal, based on complex calculations of which pairings will maximize genetic diversity and long-term survival of the world’s tallest land animal.

To avoid inbreeding, the planners first translate the relatedness of any two animals into a kinship number. For instance, .125 indicates first cousins, .25 a brother and sister, .5 a parent and offspring.

“It’s kind of like computerized dating,” said Jay Kirkpatrick, a veterinarian at ZooMontana, who pioneered the use of a contraceptive vaccine that keeps wild horses from overrunning Maryland’s Assateague Island National Seashore.

In the wild, many animals have incest-avoidance mechanisms that minimize inbreeding. For instance, young male elephants usually leave their birth group, as do young male lions, mandrills and Belding’s ground squirrels.

But captive animals aren’t free to find a new neighborhood. As a result, zoos have seen considerable inbreeding and its attendant genetic ills.

In the late 1970s, biologist Katherine Ralls found that inbreeding harmed 41 out of 44 populations at the National Zoo in Washington, D.C; a third of the offspring of siblings died.

When possible, zoos intervene. A recent contraceptive implant will increase the odds that Elinya, a young yellow-footed rock wallaby, does not breed with her father, also at the L.A. Zoo.

And since captive birds can’t fly away to avoid mating with close relatives, the zoo will send a rare male screamer -- a South American bird hatched in Los Angeles last year -- to the Palm Beach Zoo in Florida. Removing nests or putting dummy eggs in them is often enough to keep bird populations in check.

Zoo population planners think like chess players, planning far ahead, weighing kinship numbers, the health of each animal and other factors, in hopes of coming up with pairs that will produce healthy young with diverse genes.

In the future, it’s likely that all captive giraffes in North America -- except the 50 genetically distinct Masai -- will be allowed to interbreed. Giraffes are not technically endangered, and most of the 500 or so non-Masai in American zoos are hybrids -- the offspring of different subspecies.

Participating zoos are now deciding whether to continue to follow the binding directives of the Species Survival Plan or opt for a less restrictive Population Management Plan, with nonbinding breeding recommendations.

The pregnant Masai in Los Angeles is a 21-year-old named Asali, with an 18-inch purple tongue and eyelashes that look too lush to be real.

“She’s one of only two wild-caught females in North America,” said keeper Steve Tirotta.

Because of her wild parentage, Asali brings a fresh infusion to the gene pool -- in zoo speak, she is a much-sought-after “founder animal.”

Last summer, Asali mated with Artimus, a 7-year-old shipped from the San Diego Zoo and Animal Park. Their 6-foot-tall, 130-pound calf is due in September.

“We’re very excited,” said Tirotta. “It’s a new bloodline.”

While Asali and Artimus will probably breed again, Los Angeles’ 23-year-old male, Kito, is another matter.

In the past, zoos often let animals in captivity breed at will -- especially males, who pay little or no health price in reproducing. But Kito now has “DO NOT BREED” stamped next to his name in the giraffe master plan.

Having sired about 20 calves, Kito “may be No. 1, the most genetically represented Masai giraffe in North America,” said senior animal keeper Robin Noll. Conscientious animal managers “look at that and go, ‘Whoa.’ ”

However, nobody has delivered the don’t-breed message to Kito, clearly the local alpha male. The zoo could use Lupron on Kito, in effect, chemically castrating him.

“It’s also used on sex offenders to take away their sex drive,” Noll said.

But robbing Kito of his libido would also deny visitors the opportunity to see him woo a female -- part of the zoo’s educational mission.

Now that Asali is safely pregnant by a male with coveted genes, Kito is allowed near her. And, despite her pregnancy, she continues to behave in ways that arouse him. Nevertheless, Kito is able to determine that Asali is not ovulating, and eventually wanders away.

Neema, 17, already the mother of several calves, often remains cloistered in the giraffe barn, in view of the other animals but safely out of Kito’s reach. Zoo officials want her to reproduce in the future, but not yet.

Initially, Neema was on Depo-Provera, the same ovulation-interrupting drug many women use. A dart-full was shot into Neema’s flank with an air gun, a method far safer for a giraffe than one that requires anesthesia. But Depo-Provera is costly -- $1,000 a year for a giraffe, $2,000 for a hippo. And the appropriate dose, based on body weight and metabolic rate, is a matter of guesswork.

Last March, Neema was put on porcine zona pellucida vaccine, an immunocontraceptive derived from pigs’ eggs. Provided at cost -- $21 a dose -- by ZooMontana, the vaccine prevents pregnancy, but Neema continues to ovulate twice a month. And that’s a problem, given her arthritis.

“Hormonally, she still smells wonderful to the bulls, so they still want to mate with her every two weeks .... The last thing she needs is a horny boy chasing her around every couple weeks, aggravating her sore foot,” Tirotta said, explaining why she is kept apart.

In 1999, a young chimpanzee whose vasectomy failed caused three untimely pregnancies at the L.A. Zoo. Since then, the keepers have watched the chimps closely.

They make sure a female on birth-control pills actually swallows her pill, instead of hiding it in her cheek, then slipping it into another’s mouth. Often the pill is dissolved in juice or mixed with yogurt.

The keepers also make sure one tamarin, or monkey, doesn’t pick the stitches out of the incision of another who has had a surgical implant of melengestrol acetate, the synthetic form of the hormone progesterone.

And female keepers sometimes make an educated guess about how a particular contraceptive makes another female primate feel, L.A. Zoo veterinarian Leah Greer said.

An empathetic keeper of a chimp named Bonnie once told Greer: “I think Bonnie’s blue on this pill. I was blue when I was on it. I think we should switch.”

With zoo animals, contraception is never simple, no matter how much good data are available. Noll recently e-mailed Jay Kirkpatrick asking how soon Neema could be bred without fear of complications once she is off the vaccine.

Kirkpatrick’s e-mailed reply: One or two years, “if she behaves like a horse.”

Noll laughed. “That’s usually the case with exotics,” she said. “There’s so much we’re still figuring out.”