The U.S. Department of Agriculture has lifted a quarantine on two California dairy farms now that it has determined a recent outbreak of mad cow disease linked to the farms was not caused by infected cattle feed.

The department announced Friday that most cows raised with or related to the ten-year-old cow have died, saying it's unlikely other cows are infected.

The department said it is investigating around ten to 12 cows born at the same time and in the same area as the diseased cow which may be located if records are available.

The World Organization for Animal Health said it agrees with the U.S. investigation that the recent case of mad cow was atypical.