Twelve wild mares that tested positive for a lethal virus have been put to death.

The mares had 12 foals, 11 of which also tested positive. They still are being examined. Animal-rights activists contend the foals may have tested positive because of antibodies from their mothers and may not have the infectious disease.Glen Foreman, BLM spokesman, said a veterinarian euthanized the last mare Monday afternoon. The horses will be buried in a 6-foot-deep trench.

The foals could be sent to another state for research on equine infectious anemia as soon as mid-July.

The mares were the last of the positive-tested horses in the BLM's roundup in eastern Utah. An outbreak of the virus on the Ute Indian Reservation in April prompted the roundup. Of the 440 horses gathered, 60 tested positive.

A federal judge from Washington issued two reprieves this month to save the foals from euthanasia. The latest reprieve - which ends July 20 - gives the BLM a chance to try to find a state willing to take the foals.

Universities in Kentucky and Oklahoma want the foals but are awaiting approval by state veterinarians.

Researchers want to study how the virus is transferred from the mother to the foals. The BLM had kept the mares alive thinking the universities might use them in a study, but the schools said Monday that they didn't want them.

The BLM has been testing the foals' blood as part of the research. Foreman said the amount of antibodies in the positive horses is diminishing.