FORT WORTH, Texas -- A 40-year-old elephant died while trying to give birth to a calf that also died, zoo officials said.

Babe, an Asian elephant that arrived at the Fort Worth Zoo in 1991 for its breeding program, was the oldest female elephant there.

Last month as the end of her 22-month gestation period neared, elephant keepers started watching her around the clock, zoo officials said.

Babe went into labor Sunday afternoon and her contractions continued for two days, but the calf did not move into the birth canal. Although Babe rested and did normal physical activity, her health unexpectedly declined and she died Thursday morning in her sleep.

Ron Surratt, the zoo’s director of animal collections, said staffers were stunned and having a difficult time with the loss.  The zoo has six other elephants.

A necropsy showed that Babe had a torn uterus, which probably caused her death, said zoo spokeswoman Remekca Owens. The calf that died during labor was full-term, she said.

In 2002, Babe gave birth to a full-term stillborn calf.

About a third of Asian elephant births result in a dead or

stillborn calf, according to the Association of Zoos and Aquariums.  Only three Asian elephants were born in North American animal facilities last year, zoo officials said.

Two elephants, both 49 and African, died last year in Texas zoos. Tanzy died in August at the Abilene Zoo, two years after gaining national attention when zookeepers gave her the anti-anxiety drug Xanax to ease her grumpiness. Alport died in November at the San Antonio Zoo after she was diagnosed with a ligament injury.

According to a 2004 study, the average life expectancy of Asian and African elephants in captivity in North America is 45 years and 33 years, respectively.

Asian elephants, which are endangered in the wild, weigh 3 tons to 6 tons and are up to 12 feet tall, and females have small tusks that seldom protrude beyond the lip. African elephants, which are threatened in the wild, weigh 4 tons to 7 tons and are up to 14 feet tall.