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KANGAROO STUDY MAY BEGET A LEAP IN BIRTH CONTROL OPTIONS

Four kangaroos underwent innovative operations last week at the St. Louis Zoo: They got vasectomies from a medical researcher who is developing a reversible method of the birth control measure for humans.

"This is new, brand new," said Lourens Zaneveld, the researcher who performed the surgery.Zaneveld, a professor of obstetrics and gynecology at Rush Presbyterian St. Luke's Medical Center in Chicago, said he was surprised when Cheryl Asa, the Zoo's reproductive biologist, enlisted his services.

Zaneveld has been working on a method of male birth control in which silicone plugs are inserted to block the vas deferens, the duct that carries sperm from the testicles. The procedure is reversible because the silicone can be removed later.

The plugging procedure is in the clinical trial stage on humans in America. A similar method, in which liquid silicone is injected, is being used in China, Zaneveld said.

Asa said birth control is important in zoos because of the danger of inbreeding when animals are displayed in colonies. She said space limitations also are important, and the zoo has enough kangaroos and impalas.

Sterilization of animals is not considered an option for many species because that would remove them from the captive gene pool, which is becoming increasingly important as animals become threatened in the wild.

"We need contraception," she said. "Birth control pills work in great apes, but they have to be given orally each day.

"You can do that with great apes because you can put it in a raisin or something, but you couldn't do it with some other species - lions, say."

Implants containing hormones that block ovulation - much like Norplant, approved late last year for humans - also have been used in animals, she said.