Animal Identification Brochure
It is important, in most cases, to be able to identify individual animals in a study. In a few situations, small group identification may be enough if all of the animals in the group are to be treated in the same manner and if individual variations in response to a treatment are not to be accounted for separately.
Ideally, the method should ensure a permanent, indisputable identification of an individual and should not place a burden on the animal. Letters and numbers are often used to identify animals and these should not be so complex as to increase the risk of human error in the recording of data particularly in the transcription process.
Ear tags are commonly employed in farm animals (e.g., sheep, cattle) and sometimes in small laboratory animals, including mice. However, for these very small animals, the ear tags are heavy and distort the ears and are not recommended. In addition, it is often the practice to use two tags so that if one is lost, the animal will still be identified. Wing clips and leg bands are commonly used to identify birds. Collars with identification tags may be used for dogs and cats.
Tattooing, either with numbers and letters or with other codes, provides a good means of identification. There is some risk that the tattoos will fade and become illegible so they should be checked on a regular basis. Tattooing may be done on any part of the body but consideration should be given to a location where the tattoo may be read without excessive handling of the animal. Micro-tattoos which are small tattoo dots on specific parts of the body, can be useful particularly in albino animals.
Temporary or short term marking with various dyes is possible in some birds and animals, especially those with white areas of fur or feathers, or on the tails of some rodents. Marking pens may be used to apply the marks but as with other systems, the marks must be clear and the identity of the animal unmistakable. Depending on the type of marker used, renewal may be required as often as daily to ensure reliability.
Ear notching is another way of identifying small rodents and pigs, although tattooing is preferred. There is a universally recognized notching scheme for small rodents but others have devised their own pattern of coding. It is important to place the punches and notches accurately so that identification of the animal is indisputable.
The use of implantable microchips has increased since these provide a unique and tamperproof means of permanently identifying animals. These chips are glass encased passive transponders, i.e., they must be energized from outside for the information encoded on them to be released. This information is usually just an identification number but some of the newer microchips will also indicate the body temperature of the animal. The microchips and scanners are relatively expensive but are very useful where positive identification of valuable animals is required. The passive integrated transponder (PIT) tag is being widely used in salmonid aquaculture to identify tagged fish as they pass interrogation sites during their migration. The PIT microchip is implanted in the body cavity of the fish, rather than subcutaneously as in mammals.
Several of the techniques described above may be associated with pain to the animal (e.g., ear tagging, ear punching, microchip insertion, tattooing). This may necessitate the use of an analgesic. Small animals (e.g., mice) may be anesthetized with a volatile anesthetic which allows for quick recovery from the procedure. In larger animals, a local anesthetic may be sufficient to allow the procedure. For some animals, the use of a systemic analgesic like butorphanol may be sufficient to alleviate the pain.
Several other methods of identification have been used in the past but have limited if any application in the laboratory. Toe clipping to identify newborn rodents in a litter or for some wild animals (e.g., salamanders) is now considered inappropriate. Branding is also not necessary for the identification of cattle, horses, etc., as there are more humane ways to identify them. However, cattle or horses purchased from farm animal sources may have been branded previously.
Fish are often identified by clipping fins or by means of small tags on the gills or on the back.
Field biologists are interested in identifying animals to follow their activities in their home ranges or on migratory pathways. Radio transmitters are placed on a wide variety of animals from moose to small birds. These transmitters emit a radio signal that allowed the investigators to locate the source of the signals. Satellite and global positioning technology are also used. Some of these transmitters are applied externally to the feathers or fur and are designed to fall off the animal after a certain period of time. On birds, for example, the transmitter will be lost during the bird's annual molt.