More than half of the 96 baby rats that were launched on the research flight have died from starvation and dehydration. The surrogate rat mothers which readily accepted and nursed babies that were not their own on Earth either would not let them feed or did not produce enough milk for nursing in space, said NASA's chief veterinarian, Joseph Bielitzki.
"Mortality at 50 percent on this type of study is really not expected and really unacceptable," Bielitzki said Tuesday. "We will certainly conduct a detailed investigation into what the causes of this failure were."
Forty-six rats died over the weekend; some had to be killed by the astronauts because they were so sick. Four others died Monday and Tuesday, including two that the crew had to euthanize. NASA reported today that yet another young rodent had to be killed late Tuesday.
Some of the sick rats were fed a solution of Gatorade and water by hand to nurse them back to health. Astronaut-veterinarian Richard Linnehan reported Tuesday evening that the animals had improved.
"Most of the animals are looking really good right now," Linnehan told Mission Control. "We've still got a bit of morbidity, but things are settling down. I think we're OK."
The deaths prompted criticism from People for the Ethical Treatment of Animals, which accused NASA of having an "appalling record" in animal research.
"It can't keep animals alive on the ground or in space," said Mary Beth Sweetland, director of research, investigations and rescue for the animal rights group.
But shuttle Commander Richard Searfoss said Linnehan had done everything he could to prevent the deaths.
"He has been a real hero in the care and nurturing that he has given to some of the animals that had some problems," Searfoss said.
While the animals received extra care, human experiments continued Tuesday. Crew members Jim Pawelczyk and Jay Buckey had hairlike electronic needles inserted into their knees to measure blood-pressure control in weightlessness.
Likened to acupuncture, the test could help scientists learn more about a disorder that causes people to faint or feel lightheaded after standing up. Many astronauts experience those problems when they first return from space.
By Pauline Arrillaga