Every bovine animal in the UK must have an
ear tag in each ear: a
primary tag in one ear, which must be a large yellow plastic tag, and a
secondary tag in the other, which may be similar to the primary, or it may be a smaller plastic tag (usually but not always also yellow) or a metal clip. Each tag must have the cattle passport number printed or stamped upon it, and the secondary tag may also include a
RFID chip bearing the same number in electronic form. Tags may also include the passport number as a
barcode, and they may have a space for "management information" to be written by the farmer (for example a name). The British ear tag and passport number is in the format
UK HHHHHH CNNNNN – this has been in use since 2002, before which other formats were used. The current format breaks down as follows: •
UK – the country code (electronic readers read the UK country code as 826, in line with
ISO 3166); •
H – a unique six-figure number given to each herd (usually one herd per farm, or sometimes one for each bovine enterprise on a farm); •
C – a check digit from one to seven. See below for calculation. •
N – a sequential five-figure number for each calf born into that herd (with leading zeros where necessary). Numbering example: If a herd had the number
123450, its first three calves would have the numbers: •
UK 123450 600001 •
UK 123450 700002 •
UK 123450 100003 The
check digit highlights a large majority of errors in reading or recording the sequential number. A single-figure error in either the herd number sequential number will not match the check digit, unless it happens to produce a figure differing by a multiple of seven. For example, a herd number of "123456" would have to be misread as "193456", or a sequential number of "00016" would have to be misread as "00086". Similar numbering is used for sheep and goats, with the omission of the check digit (and there is no individual paper passport). The number assigned to a sheep and goat flock is usually (but not always) the same six-figure number as that assigned to a cattle herd on the same farm. For tags in
Northern Ireland, the letters “UK” followed by the unique lifetime identification number consisting of the digit “9” followed by the herd number (3 to 6 digits in length), the individual animal code (1 to 4 digits in length) and a check digit (1 digit in length), each number group separated from the previous group by a space. ==Check digit==