Bison calf conceived at Toronto Zoo with frozen sperm from 1980

Two wood bison calves are seen in this photo from the Toronto Zoo.

A wood bison calf has been born at the Toronto Zoo as a result of artificial insemination with what is believed to be the longest stored sperm used in a successful zoo birth.

Two calves were born July 21 and 28, according to a statement issued Monday. The births are being called significant for two reasons.

One of the calves is a second-generation artificially-inseminated bison. Its mother was one of six artificially-inseminated wood bison born at the zoo. The other calf was conceived from 35-year-old sperm acquired from Elk Island, Alta., in 1980.

"To our knowledge, this is the longest stored sperm used to produce a successful AI birth in a zoo species," the statement said.

The Toronto Zoo is one of only a few zoos in North America that uses "biobanking" in its reproductive lab. Biobanking refers to the process of freezing living cells, such as sperm and embryos, for the purpose of preserving genetic diversity.

"This is an excellent example of genetic material used over 'time and space': the infusion of genetics into a herd many years after the donor is gone and translocation of genetics between locations," Gabriela Mastromonaco, curator of reproductive programs and research, said in the statement.

Wood bison are considered a threatened species in Canada due to ongoing disease and heavy hunting.

The zoo has been involved in wood bison conservation since 1977, the statement said. The program includes captive breeding and reintroduction of animals back into the wild.