SAN FRANCISCO — A 350-pound Siberian tiger that mauled an experienced San Francisco Zoo keeper so badly she could lose her arm had no history of violence, prompting an investigation into what led to the vicious attack.

The tiger would likely remain on view Saturday, zoo officials said, even as the woman underwent emergency surgery to save her lacerated limb.

At least 50 visitors were at the zoo's big cat exhibit, called the Lion House, when the tiger, Tatiana, reached through her cage's iron bars and grabbed the keeper Friday afternoon, said Robert Jenkins, the zoo's director of animal care.

"We're still trying to figure out what happened and why it happened," Jenkins said.

The woman was rushed into surgery at San Francisco General Hospital and remained hospitalized Friday night. Her family requested that details of her condition not be released at this time, zoo and hospital officials said.

"My understanding is the injuries are not life-threatening, but perhaps limb-threatening," Fire Chief Joanne Hayes-White said.

The trainer has been an animal keeper at the zoo since 1997. Her main job is taking care of the zoo's four lions and three tigers, Jenkins said.

The attack happened during a regular 2 p.m. public feeding, during which keepers typically deliver a meal of fortified horse meat through a small slot.

"No matter how familiar you get with these animals, they're still wild animals," Jenkins said. "You have to have a healthy respect for them and be aware of what can happen."

The 3-year-old tiger arrived at the San Francisco Zoo from the Denver Zoo more than a year ago. There were no previous incidents of aggression against humans involving Tatiana, said Ana Bowie, a Denver Zoo spokeswoman.

The mauling was the first attack of its kind against a human at San Francisco Zoo, Jenkins said.

According to its Web site, San Francisco Zoo is one of the only zoos in the U.S. where visitors can see big cat feedings.