FRESNO, Calif. (AP) — Investigators looking into California's first case of mad cow disease say they have tracked down at least one of her offspring in another state.It was euthanized and tested for the disease, also known as bovine spongiform encephalopathy (BOH'-vyn SPUN'-ji-form en-se-fah-LAH'-puh-thee). The test was negative.USDA officials said Wednesday that the diseased cow had at least one other offspring within the last two years, but it was stillborn. They did not say how that carcass was disposed.The USDA announced April 24 that the nation's fourth case of mad cow disease was discovered in the 10-year-old cow. It had been euthanized and at a Tulare County dairy and sent to a rendering plant. That dairy and another associated with it are under quarantine.A calf ranch where the cow was raised also is under investigation.