The farm ministry began numbering all cattle in the nation Monday as part of emergency measures to cope with mad cow disease, tagging the first cow in Yamato, Gifu Prefecture.
The numbering system is being used to track all cows and to speed up the flow of information -- such as which cows might have been bred with the disease, should more mad cow cases arise.
About 270 cows at nine farms in Yamato will have been tagged by this evening, and the Agriculture, Forestry and Fisheries Ministry plans to have roughly 4.5 million beef cattle and dairy cows bearing 10-digit identification codes by March.
The ministry will also build a database to compile the cows' date of birth, breed, birthplace, movement records and other data in accordance with purchases and sales.
On Sept. 10, a cow in Chiba Prefecture was confirmed infected with mad cow disease in the nation's first case of the brain-wasting illness. Two more cases have since been officially announced.
Mad cow disease, known as Bovine Spongiform Encephalopathy, is believed to cause the human variant Creutzfeldt-Jakob disease in people who eat infected beef and has prompted widespread consumer anxiety.
The numbering system was introduced in Hokkaido, Akita, Aichi, Ehime, Kumamoto and Okinawa prefectures on an experimental basis in 2000.
But delays in tracking cows that were bred along with infected cows prompted the ministry to shift to full implementation of the system.