Microchip implant (animal)

For use in humans, see Microchip implant (human).
Microchip implant in a cat.
An RFID chip (also known as PIT tag) next to a grain of rice.

A microchip implant is an identifying integrated circuit placed under the skin of an animal. The chip, about the size of a large grain of rice, uses passive RFID (Radio Frequency Identification) technology, and is also known as a PIT tag (for Passive Integrated Transponder).

Externally attached microchips such as RFID ear tags are commonly used to identify farm and ranch animals other than horses. Some external microchips can be read with the same scanner used with implanted chips.

Uses and benefits

Animal shelters, animal control officers and veterinarians routinely look for microchips to return lost pets quickly to their owners, avoiding expenses for housing, food, medical care, outplacing and euthanasia. Many shelters place chips in all outplaced animals.

Microchips are also used by kennels, breeders, brokers, trainers, registries, rescue groups, humane societies, clinics, farms, stables, animal clubs and associations, researchers, and pet stores.

Microchips can activate some pet doors[1] programmed to recognize specific animals.

Some countries require microchips in imported animals to match vaccination records. Microchip tagging may also be required for CITES-regulated international trade in certain endangered animals: for example, Asian Arowana are tagged to limit import to captive-bred fish. Also, birds not banded who cross international borders as pets or for trade must be microchipped so that each bird is uniquely identifiable.


Information about the implant is often imprinted on a collar tag worn by a pet

Microchips can be implanted by a veterinarian or at a shelter. After checking that the animal does not already have a chip, the vet or technician injects the chip with a syringe and records the chip's unique ID. No anesthetic is required. A test scan ensures correct operation.

An enrollment form is completed with chip ID, owner contact information, pet name and description, shelter and/or veterinarian contact information, and an alternate emergency contact designated by the pet owner. Some shelters and vets designate themselves as the primary contact to remain informed about possible problems with the animals they place. The form is sent to a registry, who may be the chip manufacturer, distributor or an independent entity such as a pet recovery service. Some countries have a single official national database. For a fee, the registry typically provides 24-hour, toll-free telephone service for the life of the pet. Some veterinarians leave registration to the owner, usually done online, but a chip without current contact information is essentially useless.

The owner receives a registration certificate with the chip ID and recovery service contact information. The information can also be imprinted on a collar tag worn by the animal. Like an automobile title, the certificate serves as proof of ownership and is transferred with the animal when it is sold or traded; an animal without a certificate could be stolen.

Authorities and shelters examine strays for chips, providing the recovery service with the ID number, description and location so they may notify the owner or contact. If the pet is wearing the collar tag, the finder does not need a chip reader to contact the registry. An owner can also report a missing pet to the recovery service, as vets look for chips in new animals and check with the recovery service to see if it has been reported lost or stolen.

Many veterinarians scan an animal's chip on every visit to verify correct operation. Some use the chip ID as their database index and print it on receipts, test results, vaccination certifications and other records.

Some veterinary tests and procedures require positive identification of the animal, and a microchip may be acceptable for this purpose as an alternative to a tattoo.

Components of a microchip

A microchip implant is a passive RFID device. Lacking an internal power source, it remains inert until it is powered by the scanner.

Most implants contain three elements: a 'chip' or integrated circuit; a coil inductor, possibly with a ferrite core; and a capacitor. The chip contains unique identification data and electronic circuits to encode that information. The coil acts as the secondary winding of a transformer, receiving power inductively coupled to it from the scanner. The coil and capacitor together form a resonant LC circuit tuned to the frequency of the scanner's oscillating magnetic field to produce power for the chip. The chip then transmits its data back through the coil to the scanner.

Example of an RFID scanner used with animal microchip implants.

These components are encased in biocompatible soda lime or borosilicate glass and hermetically sealed. Barring rare complications, dogs and cats are unaffected by them.

Implant location

In dogs and cats, chips are usually inserted below the skin at the back of the neck between the shoulder blades on the dorsal midline. According to one reference, continental European pets get the implant in the left side of the neck.[2] The chip can often be felt under the skin. Thin layers of connective tissue form around the implant and hold it in place.

Horses are microchipped on the left side of the neck, halfway between the poll and withers and approximately one inch below the midline of the mane, into the nuchal ligament.

Birds are implanted in their breast muscles. Proper restraint is necessary so the operation requires either two people (an avian veterinarian and a veterinary technician) or general anesthesia.

Implanted microchips can distort magnetic resonance imaging (MRIs), including those of the spinal cord.[3]

Animal species

Horse microchipping

Many animal species have been microchipped, including cockatiels and other parrots, horses, llamas, alpacas, goats, sheep, miniature pigs, rabbits, deer, ferrets, penguins, sharks, snakes, lizards, alligators, turtles, toads, frogs, rare fish, chimpanzees, mice, and prairie dogs—even whales and elephants. The U.S. Fish and Wildlife Service uses microchipping in its research of wild bison, black-footed ferrets, grizzly bears, elk, white-tailed deer, giant land tortoises and armadillos.

Worldwide use

Microchips are not yet universal, but they are legally required in some jurisdictions such as the state of New South Wales, Australia[4] and the United Kingdom (since 6 April 2016[5]).

Some countries, such as Japan, require ISO-compliant microchips or a compatible reader on imported dogs and cats.[6]

In New Zealand, all dogs first registered after 1 July 2006 must be microchipped. Farmers protested that farm dogs should be exempt, drawing a parallel to the Dog Tax War of 1898.[7] Farm dogs were exempted from microchipping in an amendment to the legislation passed in June 2006.[8] A National Animal Identification and Tracing scheme in New Zealand is currently being developed for tracking livestock.

In April 2012 Northern Ireland became the first part of the United Kingdom to require microchipping of individually licensed dogs.[9] Dog microchipping became mandatory in England on 6 April 2016.[10]

In Israel, microchips in dogs are mandatory.

Australia has a National Livestock Identification System.

The United States uses the National Animal Identification System for farm and ranch animals other than dogs and cats. In most species except horses, an external eartag is typically used in lieu of an implant microchip. Eartags with microchips or simply stamped with a visible number can be used. Both use ISO 15 digit microchip numbers with the U.S. country code of 840.

Cross-compatibility and standards issues

In most countries, pet ID chips adhere to an international standard to promote compatibility between chips and scanners. In the United States, however, three proprietary types of chips compete along with the international standard. Scanners distributed to United States shelters and veterinarians well into 2006 could each read at most three of the four types. Scanners with quad-read capability are now available and are increasingly considered required equipment. Older scanner models will be in use for some time, so United States pet owners must still choose between a chip with good coverage by existing scanners and one compatible with the international standard. The four types include:

Numerous references in print state that the incompatibilities between different chip types are a matter of "frequency". One may find claims that early ISO adopters in the United States endangered their customers' pets by giving them ISO chips that work at a "different frequency" from the local shelter's scanner, or that the United States government considered forcing an incompatible frequency change. These claims were little challenged by manufacturers and distributors of ISO chips, although later evidence suggests the claims were disinformation. In fact, all chips operate at the scanner's frequency. Although ISO chips are optimized for 134.2 kHz, in practice they are readable at 125 kHz and the "125 kHz" chips are readable at 134.2 kHz. Confirmation comes from government filings that indicate the supposed "multi-frequency" scanners now commonly available are really single-frequency scanners operating at 125, 134.2 or 128 kHz. In particular, the United States HomeAgain scanner didn't change excitation frequency when ISO-read capability was added; it's still a single frequency, 125 kHz scanner.[21]

Scanner Compatibility table for chip types used in pets
Expected results for chip type
(OK=Good read
NR=No read
DO=Detect Only with no number given)
Scanner to test ISO Conformant Full Duplex chip AVID Encrypted "FriendChip" Original U.S. HomeAgain, AVID Eurochip,[Note 7] or FECAVA "Trovan Unique" and current AKC CAR chips
Minimal ISO Conformant Scanner (also must read HALF Duplex chips common in livestock ear tags) OK NR NR NR
AVID Basic U.S. Scanner[22] NR OK NR NR
AVID Deluxe U.S. Scanner NR OK OK NR
AVID Universal Scanner sold outside U.S.[23] OK OK OK NR Assumed
AVID MiniTracker Pro Scanner announced August 2008[24] OK OK OK NR according to some (Few have seen one.)
Various vintages of U.S. HomeAgain "Universal" Shelter Scanners by Destron/Digital Angel Corp. NR,DO, or OK OK OK Possibly all OK
Typical Destron/Digital Angel Corp. U.S. Veterinarian's scanner pre-2007


Trovan LID-560-MULTI per mfr. specifications on Web[26] OK OK OK OK
U.S. Trovan Pocket Scanner per AKC-CAR Web Site[27] DO OK OK OK
U.S. Trovan ProScan700 per AKC-CAR Web Site[28] OK OK OK OK
Original 2006 Datamars Black Label Scanner[29] OK OK OK OK but Reliability Questioned
Datamars Black Label Scanner "classypets" model[30] OK NR or DO? OK OK but Reliability Questioned
Banfield-Distributed 2004-2005 Vintage Datamars Scanners OK Possibly all DO OK Possibly all OK but Reliability Questioned (Undocumented Feature)
Datamars Minimax and Micromax[31] OK NR NR NR
Typical Homemade Scanner[32] OK OK but extra step required (web-based decryption service) OK OK

(For users requiring Shelter-Grade certainty, this table is not a substitute for testing the scanner with a set of specimen chips. One study[33] cites problems with certain Trovan chips on the Datamars Black Label scanner. In general, the study found none of the tested scanners to read all four standards without some deficiency. The study predates the most recent scanner models, however.)

Reported adverse reactions

RFID chips are used in animal research, and at least three studies conducted since the 1990s have reported tumors at the site of implantation in laboratory mice and rats.[34] Noted veterinary associations[35] responded with continued support for the procedure as reasonably safe for cats and dogs, pointing to rates of serious complications on the order of one in a million in the U.K., which has a system for tracking such adverse reactions and has chipped over 3.7 million pet dogs. A recent study found no safety concerns for microchipped animals with RFID chips undergoing MRI at one Tesla magnetic field strength.[36] In 2011 a microchip-associated fibrosarcoma was reported found in the neck of a 9-year old, neutered-male cat. Histological examination was consistent with postinjection sarcoma, but all prior vaccinations occurred in the hindlegs.[37]

See also


  1. For display, typically the three country/manufacturer code digits are followed by twelve digits of serial number to make a 15-digit numeric string.
  2. Curiously, an actual matching descriptive specification from the Federation of European Companion Animal Veterinary Associations, or one from Destron Corporation, remains illusive.
  3. The differences are obvious and easily surmounted by someone trying to make a scanner for a FECAVA chip specimen, so the Annex is still quite useful. (The actual FECAVA frequency-modulated signals are inverted (backwards) from the Annex specification.)
  4. This is found in clauses 2 and 6 of ISO 11785; the two actual conformant 64-bit types are described in clauses 6.1 and 6.2.
  5. Few of the petitioners bothered to ask AVID to add Trovan-chip compatibility at that time, as these chips would remain uncommon and obscure until 2007 in the U.S.
  6. In addition to its current scanners with full support for ISO full duplex chips, and maybe ten years production of earlier scanners with no ISO support, Destron/Digital Angel Corp. is also reported to have made in-between models circa 2006, one that gives a detection indication, but no number for ISO chips, and one model that gives either simple detection or full number readout, depending perhaps on the chip's manufacturer or some other factor. These models may be hard to discern without many specimen chips; upgrades may be available, especially to current customer partners of HomeAgain.
  7. A mention of a chip type called "AVID Travelchip" has been removed from this heading. It appears that "Travelchip" was actually a trademark not of AVID itself but of a chip distributor, which used it as a blanket term for several different chip types sold in value-added kits- firstly AVID Eurochips, later HomeAgain types both regular and ISO.


  1. Sureflap microchip cat flap
  2. Microchip Implantation Sites (World Small Animal Veterinary Association).
  3. Saito M, Ono S, Kayanuma H, Honnami M, Muto M, Une Y (May 2010). "Evaluation of the susceptibility artifacts and tissue injury caused by implanted microchips in dogs on 1.5 T magnetic resonance imaging". J. Vet. Med. Sci. 72 (5): 575–81. doi:10.1292/jvms.09-0386. PMID 20086326.
  4. WSAVA - Australian Microchip Standard
  5. Entering Japan: Dogs & Cats.
  6. Masters, Catherine (25 March 2006). "The year of the dog war". The New Zealand Herald. Retrieved 25 October 2011.
  7. Farm Dogs Exempted from Microchipping
  8. BBC news story about introduction of law.
  9. "Dog microchipping becomes compulsory across UK". BBC News. 2016-04-06. Retrieved 2016-10-19.
  10. Pet's Death Rekindles Electronic ID Debate in JAVMA News
  11. Trovan Chips Adopted by Los Angeles in 1996.
  12. http://www.rfidnews.com/avidopenletter.html
  13. "B" Country List (Search for "Home Again microchips are ISO compatible" in the text.)
  14. ISO Standards Discussion (Search for "as compliant" in the text.)
  15. The TRAVELchip Single (Search for "Complies with" in the text.)
  16. ISO Standards Combined Text ("FECAVA" discussion starts on page 16 of the PDF file.)
  17. Pet's Death Rekindles Electronic ID Debate in JAVMA News (Search for "best" in the text.)
  18. APHIS Comment Submission from Digital Angel Corp (page 2, item 4 in the referenced .doc file.)
  19. Avid Announces New Scanner to Reunite More Lost Pets with Their Families
  20. U.S. FCC database search form (Submit the form with "Grantee Code" and "Product Code" for each individual scanner; for the new universal Digital Angel/HomeAgain Scanner, still operating at 125 kHz codes "C5S" and "HS9250L"; for a recent AVID scanner, operating at 134.2 kHz, codes "IOL" and "-134-AV1034I" .)
  21. Descriptions of AVID Scanners (Search for "only the AVID" in the text.)
  22. Test Results from American Humane (Search for "in use in canada" in the text.)
  23. Avid Announces New Scanner.
  24. Test Results from American Humane (Search for "unless vet is with a shelter" in the text.)
  25. Trovan Multi Scanner specifications (Apparently applies to models sold outside U.S.)
  26. Using The AKC-CAR Multi-System Pocket Scanner (U.S. Model says "Detect Only" on ISO chip type.)
  27. AKC CAR Scanners
  28. Datamars Multi Scanner specifications.
  29. Datamars Multi Scanner specifications.
  30. Datamars Scanner Descriptions.
  31. Software for Homemade Scanners- Chip Type Listing.
  32. Nov. 2007 Scanner Evaluation from EID Limited.
  33. Lewan, Todd. "Chip Implants Linked to Animal Tumors". The Washington Post. Retrieved 12 May 2010.
  34. Position Statement from World Small Animal Veterinary Association.
  35. Baker, Martin A.; MacDonald, Iain (2011). "Evaluation of veterinary radiofrequency identification devices at 1T". Veterinary Radiology & Ultrasound. 52 (2): 161. doi:10.1111/j.1740-8261.2010.01762.x.
  36. Carminato A, Vascellari M, Marchioro W, Melchiotti E, Mutinelli F (December 2011). "Microchip-associated fibrosarcoma in a cat". Vet. Dermatol. 22 (6): 565–9. doi:10.1111/j.1365-3164.2011.00975.x. PMID 21535253.
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