Exhausted from a two-week flight that killed many of the animals on board, Columbia's astronauts said the casualty rate would have been higher if they hadn't set up an intensive care unit and supplied nonstop TLC.

As it was, 57 of 96 baby rats came back dead, victims of maternal neglect."When you initially see this, you say, `Oh, no!' Then we started treating. I guess the veterinarian in me kicked in," Richard Linnehan said late Sunday after the space shuttle landed, ending a 16-day mission that was the most in-depth study ever into how the brain operates in space.

Scientists want that question answered before planning possible moon colonies or a trip to Mars. Linnehan said the mission also provided immediate lessons for the international space station, to be assembled in orbit beginning this year.

The mortality rate was even higher among the young sword-tail fish that flew on the mission: 200 dead out of 225, most likely because their water was too warm. But the astronauts didn't learn about that until after they landed; they didn't have access to the fish in orbit.

They did have access to the rats, however, and did everything in their power to save the tiny, emaciated rodents once it became clear they were quickly dying of dehydration.

To the crew's astonishment and dismay, the surrogate mother rats couldn't - or wouldn't - feed the young animals.

"I've been a zoo veterinarian. I've been a laboratory animal veterinarian. I've worked on animals from newts all the way up to rhinoceroses," Linnehan said. "So we get up there and we opened up the cage and we saw this and I'm like, `Well, this doesn't look good.' "

As the astronaut in charge of Columbia's lab and the only veterinarian on board, Linnehan immediately assembled a critical care unit. Night after night, after their other work was done, he and his crewmates tended to the rats: They fed them, warmed them, washed them and dried them - one by one.

"I got my crash course in veterinary emergency medicine from Rick, and I think it worked out really well," said astronaut-physician Dave Williams.

The four medical men on board made do with four or five hours of sleep a night for several nights in a row. Commander Richard Searfoss fretted about his crew's health, even though no one complained.

After landing Sunday, the astronauts were hustled off Columbia. Six of the seven crew members left on stretchers; doctors wanted them reclining to preserve the lingering effects of their weightlessness. Ten hours later, they were still undergoing medical exams; the tests were expected to go on for days.

Linnehan said that on future flights, young animals' cages must be improved. The baby rats aboard Columbia simply floated away from their surrogate mothers and couldn't figure out how to get back to nurse. The mother rodents also were stressed out by the strange space environment.