Overview
An ear tag usually carries an Animal Identification Number (AIN) or code for the animal, or for its herd or flock. This identification number (ID) may be assigned by some national organisations (usually in the form of Property Identification Code, or PIC), or they may be handwritten for the convenience of the farmer ("management tags"). 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 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, each bovine animal having a passport document and tag in each ear carrying the same number. Sheep and goats in the EU have a tag in each ear carrying the official number of their flock and also 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).
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. 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; see below), implanted RFID tags (mice are too small to wear an ear tag containing an RFID chip), and dye.
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