Yellowstone Bison Bronx Zoo

In this July 4, 2012 photo provided by the Wildlife Conservation Society, a male American bison calf walks with its surrogate mother at the Bronx Zoo. The purebred Yellowstone bison was born at the Bronx Zoo on June 20, 2012 after scientists were able to successfully implant a genetically pure embryo into a the commercial bison joining the calf. (AP Photo/Wildlife Conservation Society, Julie Larsen Maher)

Julie Larsen Maher

DENVER — A purebred Yellowstone bison is growing up at the Bronx Zoo after scientists were able to successfully implant a genetically pure embryo into a commercial bison.

The zoo and Colorado State University announced Thursday that the surrogate bison gave birth to a healthy male calf at the zoo on June 20.

In October 2011, a team led by reproductive physiologist Jennifer Barfield took embryos from Yellowstone bison kept at a federal facility at the university, washed them free of disease and implanted them in a group of surrogates. An ultrasound two months later revealed that one was pregnant and that bison was taken to the zoo in New York City, along with the other bison, in April.

While many bison have been bred with cattle, Yellowstone National Park has one of the world's largest and most genetically pure bison herds. However, about 40 percent test positive for exposure to brucellosis, which can cause pregnant animals to miscarry. Concern about the disease has prevented the animals from being taken out of the park to reproduce.

The zoo and Barfield both said it was the first time a genetically pure bison has been born as a result of an embryo transfer.

"It gives us an avenue to bring some of their valuable genes out of the Yellowstone population," Barfield said of the technique.

The zoo has long been interested in establishing a breeding herd of genetically pure bison that can help establish herds at other zoos. The new calf however will not go on exhibit.

"The Bronx Zoo played an important historical role in the recovery of the American bison. By establishing a pure herd the zoo will be, in essence, returning to its roots," Pat Thomas, the zoo's general curator and associate director and the vice president of the Wildlife Conservation Society, said in a statement.

Another round of embryo transfers is planned for the fall.

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