Scientists bemoaned a judge's decision halting the killing of bison inside Yellowstone for disease research.

Three pregnant bison were shot by national park rangers Monday before U.S. District Judge George Revercomb in Washington, acting on a request from animal-rights activists, issued a restraining order pending a hearing April 15."Just three animals - what can you say?" said Jay Kirkpatrick, a veterinary reproductive physiologist at Eastern Montana College. "Twenty-five was the absolute minimum number to make these experiments statistically sound."

But Wayne Pacelle, national director of the Fund for Animals, called the decision "a stay of execution" for the bison.

"They can still get accurate and useful information without shooting pregnant cows," said Pacelle, whose group sought the restraining order. "We acknowledge that the data are useful, but the end doesn't justify the means."

Plans had called for killing 25 bison so that scientists could determine how many Yellowstone bison are infected with the contagious disease brucellosis and whether the disease is the same strain that can infect cattle.

Brucellosis, which is spread by contact with body fluids, can cause cattle to abort. It also can cause incurable undulant fever in humans. The disease's symptoms include fever, headaches, depression and general aching.

"We're disappointed," said Don Davis, the veterinary pathologist from Texas A&M University who heads the research team. "We're not happy to see any animals killed. But that's the only way to get the information we need."