HANFORD, Calif. (AP) — Federal and state agriculture officials are working to find out more about a California dairy cow that was found to have mad cow disease.

The finding announced yesterday is the first new case of the fatal brain disease in the U.S. since 2006 and only the fourth ever discovered in the country.

The cow died at a dairy and was randomly selected for testing at a transfer facility. A plant official says the cow had exhibited no outward symptoms of the disease.

Agriculture officials say the animal had an atypical form of mad cow, meaning it did not get the disease from eating infected cattle feed. A veterinary expert calls the case "a random mutation."

California health and food officials are assuring consumers that the food supply is safe, noting that the cow had not been headed for human consumption and people cannot get the disease from drinking milk.

The head of the Western United Dairymen says state and federal officials plan to test other cows that lived in the same feeding herd as the infected cow.