An ear tag is a plastic or metal object used for identification of domestic livestock and other animals. If the ear tag uses Radio Frequency Identification Device (RFID) technology it is referred to as an electronic ear tag. Electronic ear tags conform to international standards ISO 11784 and ISO 11785 working at 134.2 kHz, as well as ISO/IEC 18000-6C operating in the UHF spectrum. There are other non-standard systems such as Destron working at 125 kHz. Although there are many shapes of ear tags, the main types in current use are as follows:
Flag-shaped ear tag: two discs joined through the ear, one or both bearing a wide, flat plastic surface on which identification details are written or printed in large, easily legible script.
Button-shaped ear tag: two discs joined through the ear.
Plastic clip ear tag: a moulded plastic strip, folded over the edge of the ear and joined through it.
Metal ear tag: an aluminium, steel or brass rectangle with sharp points, clipped over the edge of the ear, with the identification stamped into it.
Each of these except the metal type may carry a RFID chip, which normally carries an electronic version of the same identification number.
An ear tag usually carries an Animal Identification Number (AIN) or code for the animal, or for its herd or flock. Non electronic ear tags may be simply handwritten for the convenience of the farmer (these are known as "management tags"). Alternatively this identification number (ID) may be assigned by an organisation, such as the Meat and Livestock Association (MLA).Electronic tags may also show other information about the animal, including other related identification numbers; such as the Property Identiﬁcation Code (PIC) for the properties the animals have been located. In the case of MLA's NLIS the movement of certain species of livestock (primarily cattle, goats and sheep) must be recorded in the online database within 24 hours of the movement; and include the PICs of the properties the animals are travelling between. The National Livestock Identification System (NLIS) of Australia regulations require that all cattle be fitted with a RFID device in the form of an ear tag or rumen bolus (a cylindrical object placed in the rumen) before movement from the property and that the movement be reported to the NLIS. However, if animals are tagged for internal purposes in a herd or farm, IDs need not be unique in larger scales. The NLIS now also requires sheep and goats to use an ear tag that has the Property Identiﬁcation Code inscribed on it. These ear tags and boluses are complemented by transport documents supplied by vendors that are used for identification and tracking. A similar system is used for cattle in the European Union (EU), each bovine animal having a passport document and tag in each ear carrying the same number (see British Cattle Movement Service). Sheep and goats in the EU have a tag in one or both ears carrying the official number of their flock and also for breeding stock an individual number for each animal; one of these tags (usually the left) must have a RFID chip (or the chip may instead be carried in a rumen bolus or on an anklet).
An ear tag can be applied with an ear tag applicator, however there are also specially-designed tags that can be applied by hand. Depending on the purpose of the tagging, an animal may be tagged on one ear or both. There may be requirements for the placement of ear tags, and care must be taken to ensure they are not placed too close to the edge of the ear pinnae; which may leave the tag vulnerable to being ripped out accidentally. If there exists a national animal identification programme in a country, animals may be tagged on both ears for the sake of increased security and effectiveness, or as a legal requirement.If animals are tagged for private purposes, usually one ear is tagged. Australian sheep and goats are required to have visually readable ear tags printed with a Property Identiﬁcation Code (PIC). They are complemented by movement documents supplied by consignors that are used for identification and tracking.
Very small ear tags are available for laboratory animals such as mice and rats. They are usually sold with a device that pierces the animal's ear and installs the tag at the same time. Lab animals can also be identified by other methods such as ear punching or marking (also used for livestock), implanted RFID tags (mice are too small to wear an ear tag containing an RFID chip), and dye.
Other forms of animal identification
Pigs, cattle and sheep are frequently earmarked with pliers that notch registered owner and/or age marks into the ear. Mares on large horse breeding farms have a plastic tag attached to a neck strap for identification; which preserves their ears free of notches. Dairy cows are sometimes identified with ratchet fastened plastic anklets fitted on the pastern for ready inspection during milking; however NLIS requirements apply to cattle - including both dairy and beef animals. More commonly coloured electrical tape is used as short term ankle identifiers for dairy animals to identify when one teat should not be milked for any reason. Laboratory rodents are often marked with ear tags, ear notches or implantable microchips.
The National Livestock Identification System (NLIS) Australia, formerly used cattle tail tags for property identification and hormone usage declaration.