SAN ANTONIO -- A federal complaint has been filed with the U.S. Department of Agriculture alleging inadequate conditions at the San Antonio Zoo.

"We're concerned that the zoo plans to bring in another elephant into an exhibit that really isn't fit to hold just one," said Catherine Doyle, a captive elephant specialist with the group In Defense For Animals.

The group and other animal advocates say Lucky, the zoo's lone elephant, should be retired to a sanctuary in Tennessee.

"She's looking good now. I've seen her today and I saw her yesterday and she's moving well," said Dr. Mel Richardson, Lucky's former veterinarian for five years.

Yet, Richardson said that he's still concerned about her health.

"I know what she had when I left. I don't think it went away," said Richardson, who believes Lucky showed signs of arthritis in her feet as a result of walking on concrete after 47 years of captivity.

Zoo director Steve McCusker disagrees.

"She's on dirt. She's got full pool she can get in. There's grass growing in that facility," McCusker said. "They don’t notice those things."

McCusker also said the female elephant, alone now for two years since her companion had to be put down, does not need to go to a sanctuary.

"Lucky is fine here. Lucky is healthy. Lucky is content," said McCusker, who calls many of the allegations serious, but incorrect.

In an effort to confirm Lucky's condition, Richardson has requested that the zoo to allow him to review its records.

But McCusker has refused to release Lucky's medical records.

"We have offered for them to come in and look at them," McCusker said.

Whether another elephant is brought in to keep Lucky company may depend on the outcome of the USDA investigation into the complaint filed by In Defense of Animals.

A new, larger native habitat for elephants at the San Antonio Zoo will be part of Phase 3 of its Africa Live exhibition. But McCusker said that's still several years away, depending on funding.

McCusker said when that happens Lucky will not be relocated. Instead, she will live out her days at the San Antonio Zoo.

"Elephants mean money. It's what makes the world go around. It's a business," Richardson said of the zoo's rejection to allow Lucky to go to a sanctuary.