Microchip implant (animal)

Microchip implant (animal)
Microchip implant in a cat.

A microchip implant is an identifying integrated circuit placed under the skin of a dog, cat, horse, parrot or other animal. The chips are about the size of a large grain of rice and are based on a passive RFID (Radio Frequency Identification) technology.

The use of externally attached microchip devices such as RFID ear tags (piercings rather than implants) is another, related method commonly used for identifying farm and ranch animals other than horses. In some cases the external microchips may be readable on the same scanner as the implanted style.


Uses and benefits

Microchips have been particularly useful in the return of lost pets. They can also assist where the ownership of an animal is in dispute.

Animal shelters and animal control centers benefit using microchip identification products by more quickly and efficiently returning pets to their owners. When a pet can be quickly matched to its owner, the shelter avoids the expense of housing, feeding, providing medical care, and outplacing or euthanizing the pet. Microchipping is becoming standard at shelters: many require all outplaced animals to receive a microchip, and provide the service as part of the adoption package. Animal-control officers are trained and equipped to scan animals.

In addition to shelters and veterinarians, microchips are used by kennels, breeders, brokers, trainers, registries, rescue groups, humane societies, clinics, farms, stables, animal clubs and associations, researchers, and pet stores.

Several countries require a microchip when importing an animal to prove that the animal and the vaccination record match. Microchip tagging may also be required for CITES-regulated international trade in certain rare animals: for example, Asian Arowana are so tagged, in order to ensure that only captive-bred fish are imported.

System of recovery

Effective pet identification and recovery depend on the following:

  • A pet owner either adopts a pet at a shelter that microchips some or all adoptee animals, or the owner with an existing pet brings it to a veterinarian (or a shelter) that provides the service.
  • The shelter or veterinarian does a pre-scan to verify that the animal initially does not have a chip, selects a microchip from their stock, makes a note of that chip's unique ID, and then inserts the chip into the animal with a syringe. The injection requires no anesthetic.
  • Before sending the animal home, the vet or shelter performs a test scan on the animal. This helps ensure that the chip will be picked up by a scanner, and that its unique identifying number will be read correctly.
  • An enrollment form is completed with the chip number, the pet owner's contact information, the name and description of the pet, the shelter's and/or veterinarian's contact information, and an alternate emergency contact designated by the pet owner. (Some shelters or vets, however, choose to designate themselves as the primary contact, and take the responsibility of contacting the owner directly. This allows them to be kept informed about possible problems with the animals they place.) The form is then sent to a registry keeper to be entered into its database. Depending on regional custom, selected chip brand, and the pet owner's preference, this registry keeper might be the chip's manufacturer or distributor, or an independent provider. In some countries a single official national database may be used. After receiving a registration fee, the registry keeper typically provides a 24-hour, toll-free telephone service for pet recovery, good for the life of the pet. Some veterinarians do not complete the registration on the owner's behalf. In these situations, the owner must register the animal, usually through an online application. A failure to complete this step will lead to a pet whose chip can be read but whose owner cannot be contacted due to the lack of information associated to the chip's unique ID.
  • The pet owner is also provided the chip ID and the contact information of the recovery service. This is often in the form of a collar tag imprinted with the chip ID and the recovery service's toll-free number, to be worn by the animal along with a certified registration certificate that can be sold/transferred with the pet. This ensures proper identification when an animal is sold or traded. A microchipped animal being sold or traded without a matching certificate could be a stolen animal.
  • If the pet is lost or stolen, and is found by local authorities or taken to a shelter, it is scanned during intake to see if a chip exists. If one is detected, authorities need to figure out which recovery service has the owner record, because there may be several different ones, each competing for the patronage of the pet owner. (Issues and solutions dealing with the problem of multiple registries have been moved to the article Pet recovery service.) They then call the recovery service and provide them the ID number, the pet's description, and the location of the animal. If the pet is wearing the collar tag, anyone who finds the pet can call the toll-free number, making it unnecessary to involve the authorities. (The owner can also preemptively notify the recovery service directly if a pet disappears. This is useful if the pet is stolen, and is taken to a vet who scans it and checks with the recovery service.)
  • The recovery service notifies the owner that the pet has been found, and where to go to recover the animal.

Many veterinarians perform test scans on microchipped animals every time the animal is brought in for care. This ensures the chip still performs properly. Vets sometimes use the chip ID as the pet's ID in their databases, and print this number on all outgoing paperwork associated with its services, such as receipts, test results, vaccination certifications, and descriptions of medical or surgical procedures.

Components of a microchip

Microchips are passive, or inert, RFID devices and contain no internal power source. They are designed so that they do not act until acted upon.

Most microchips comprise three basic elements: A silicon chip (integrated circuit); a coil inductor, or a core of ferrite wrapped in copper wire; and a capacitor. The silicon chip contains the identification number, plus electronic circuits to relay that information to the scanner. The inductor acts as a radio antenna, ready to receive electrical power from the scanner. The capacitor and inductor act as a tuner, forming an LC circuit. The scanner presents an inductive field that excites the coil and charges the capacitor, which in turn energizes and powers the IC. The IC then transmits the data via the coil to the scanner.

Example of an RFID scanner used with animal microchip implants.

These components are encased in a special biocompatible glass made from soda lime, and hermetically sealed to prevent any moisture or fluid entering the unit. Barring rare complications, dogs and cats are not affected physically or behaviorally by the presence of a chip in their bodies.

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. Continental European pets may be an exception; they get the implant in the left side of the neck, according to one reference.[1] The chip can often be manually detected by the owner by gently feeling the skin in that area. It stays in place as thin layers of connective tissue form around the biocompatible glass which encases it.

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

Birds' microchips are injected into their breast muscles. Because proper restraint is necessary, the operation either requires two people (an avian veterinarian and a veterinary technician), or general anesthesia is administered.

Animal species

Horse microchiping

Many species of animals have been microchipped, including cockatiels and other parrots, horses, llamas, alpacas, goats, sheep, miniature pigs, rabbits, deer, ferrets, penguins, 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 in universal use, but there are legal requirements in some jurisdictions, such as the state of New South Wales, Australia.[2] Some countries, such as Japan, require ISO-compliant microchips on dogs and cats being brought into the country, or for the person bringing the pet into the country to also bring a microchip reader that can read the non-ISO-compliant microchip.[3]

In New Zealand, all dogs first registered after 1 July 2006 are to be microchipped. Farmers protested that farm dogs should be exempt, drawing a parallel to the Dog Tax War of 1898.[4] Farm dogs were exempted from microchipping in an amendment to the legislation passed in June 2006.[5] A National Animal Identification and Tracing scheme in New Zealand is currently being developed for tracking livestock.

Australia has a National Livestock Identification System.

The National Animal Identification System is used in the United States. (It is applicable to farm and ranch animals rather than dogs and cats, and in most species other than horses, an external eartag device is typically used rather than an implant microchip. Eartags with microchips or those having only a visible stamped number can be used; either way, the 15 digit numbering scheme of the ISO type microchips is followed, using the U.S. country code of 840.)

Cross-compatibility and standards issues

In most countries, ID chips used in pets follow an international standard, enabling wide compatibility between the chips and scanners. But in the U.S., three proprietary types of chips compete for market share, along with the international type. Scanner models distributed to U.S. shelters and vets well into 2006 could each read at most three of the four types. (These "types" are also known as transmission protocols or standards) But now, several scanner models with quad-read capability are available, and increasingly, vets and shelters are considering these required equipment. Older scanner models continue to be distributed, and may be in use for some time, so U.S. pet owners still face a choice of getting a chip that gets best coverage on the older style scanners in use locally, or a chip with best acceptance in international travel. The four types include:

  • The ISO Conformant Full Duplex type is the pet chip type with the most international acceptance, being common in many countries including those of Europe since the late 1990s, and now widely adopted in Canada. It is one of two chip protocol types (along with the "Half Duplex" type sometimes used in farm and ranch animals) which conform to International Organization for Standardization standards ISO 11784 and ISO 11785. To support international/multivendor application, each of these chips contains either a manufacturer code.(99 manufacturer codes from 900 to 998 are supported.) or a country code (Values below 900 are assigned as country codes.) along with its main identifying serial number.[Note 1] In the U.S., the distributing organizations that introduced this type of pet chip have faced controversy. When 24PetWatch.com in 2003 and more famously Banfield Pet Hospitals in 2004 began distributing them, many shelter scanners in use couldn't read them. (Some still can't; asking local shelters about this may be a good idea even today.) At least one of the Banfield-chipped pets was discovered to have been needlessly euthanized,[6] and Americans debated the cause. Specifically, did this happen because "foreign" chips were sold to unsuspecting pet owners, or because scanners which were passed off as a Shelter-Grade product couldn't cope with "internationally standardized" chips? Or maybe both?
  • The Trovan Unique type is another pet chip protocol type used in U.S. pets beginning in 1990.[7] Then, due to patent problems, Trovan's implanter device was withdrawn from distribution in the United States and they became uncommon in U.S. pets, although Trovan's original registry database "infopet.biz" remained in operation. In early 2007, the American Kennel Club's chip registration database service, AKC Companion Animal Recovery Corp., "akccar.org", which had earlier been the authorized registry for HomeAgain brand chips made by Destron/Digital Angel corp., began distributing Trovan chips with a different implanter. These chips are read by the Trovan, HomeAgain (Destron Fearing), and Bayer (Black Label) readers. Despite multiple offers from Trovan to AVID [8] to license the technology to read the Trovan chips, AVID continues to distribute readers that do not read Trovan or the ISO compliant chips.
  • A third type sometimes known as FECAVA type or Destron type[Note 2] is available under various brand names. These include, in the U.S., "Avid Eurochip", the common current 24PetWatch chips, and the original (and still popular) style of HomeAgain chips. (although on request, U.S. HomeAgain and 24Petwatch now can supply the true ISO chip instead.) Chips of this type have 10 digit [hexadecimal] chip numbers. This "FECAVA" type is readable on a wide variety of scanners in the U.S., and has been less controversial, although its level of adherence to the ISO standards is sometimes exaggerated in some descriptions.[9][10][11] The ISO standard has an annex (appendix) describing three older chip types considered worthy of legacy support by scanners, and a 35-bit "FECAVA"/"Destron" type is one of them.[12] The common Eurochip/HomeAgain chips don't really agree with the annex description perfectly, although the differences might be considered overlookable by some.[Note 3] But the ISO standard also makes it clear[Note 4] that even chips (like the Trovan Unique chip) that do match one of the descriptions in the Annex are not "conformant"; only its 64-bit "full-duplex" and "half-duplex" types are "conformant". More visibly, the "FECAVA" type can't fit the ISO standard's required country codes or manufacturer codes. These chips, when implanted in traveling pets, may possibly be accepted by authorities in many countries where ISO chips are the norm, but not those that require literal ISO conformance.
  • Finally, there's the AVID brand Friendchip type, which is peculiar due to its encryption characteristics. The simple fact that a cryptographic feature is provided in a chip would not necessarily be unwelcome; few pet rescuers or humane societies would object to a chip design that outputs an ID number "in the clear" for anyone to read, and, in addition, has authentication features for use by scanners that know how to use them, for detection of counterfeit chips. But the "Friendchips" have been found lacking in actual authentication features, and rather easy to counterfeit well enough to fool the AVID scanner. Although there's no authentication encryption involved, there is obfuscation encryption, meaning decryption secrets are needed, to convert what the chip transmits into its original label ID code. Well into 2006, scanners containing the secrets were provided to the U.S. market only by AVID and Destron/Digital Angel Corp.; Destron/Digital Angel put the decryption feature in some, but not all, of its scanners possibly as early as 1996. (For years, typically its scanners distributed to shelters through HomeAgain had full decryption, while many sold to vets would just flash a message that an AVID chip had been found.) And well into 2006, both of these were resisting calls from consumers and welfare group officials to bring scanners to the U.S. shelter community combining AVID decryption capability with full ability to read ISO pet chips. Some complained[13] that AVID itself had long marketed combination pet scanners (compatible with all common pet chips except possibly Trovan) outside the U.S., and by keeping such technology out of the U.S., it could be considered partly culpable in the missed-ISO chips problem others blamed on Banfield.[Note 5] In 2006, the European manufacturer Datamars, a supplier of ISO chips used by Banfield and others, gained access to the decryption secrets, and began supplying scanners using them to U.S. customers. This "Black Label" scanner was the first four-standard full-multi pet scanner in the U.S. market. Then later in 2006 Digital Angel Corp. announced[14] it would supply a full-multi scanner in the U.S.[Note 6] Finally in 2008 AVID itself announced[15] a "breakthrough" scanner, although AVID's is still so uncommon in the field as of October 2010 that it's unclear whether it has support for the Trovan chip. Trovan itself also got the decryption technology somehow along the way, by 2006 or earlier, and now provides it in scanners distributed in the U.S. by AKC-CAR. (Some of these are quad-read, but others lack full support for the ISO chip.)

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 U.S. endangered their customers' pets by giving them ISO chips that work at a "different frequency" from the local shelter's scanner, or that the U.S. government considered forcing a change to a chip type that didn't operate at the same frequency as existing chips. The spread of these claims was little challenged by the manufacturers and distributors of the ISO chips, although later evidence suggests the claims were disinformation. In fact, all the pet chips operate slaved to the frequency of the scanner, and in practice, the ISO chips, although by design optimized to work best when given excitation energy at 134.2 kilohertz, have quite good readability working with 125 kilohertz excitation. Likewise, the "125 kilohertz" chip types are readable at 134.2 kilohertz. Confirmation of this comes from government filings which indicate that the supposed "multi-frequency" scanners now commonly available are really single-frequency scanners (each operating at 125 or 134.2 kHz, or an in-between frequency like 128 kHz.) In particular, the U.S. HomeAgain scanner didn't really change its excitation frequency when ISO-read capability was added; it's still a single frequency, 125 kHz scanner.[16]

Banfield Pet Hospitals for a length of time advocated and practiced double chipping with both ISO and "FECAVA" type chips. (By December 2009 they had switched back to ISO-only.) A consequence of an animal having multiple chips for any reason, whether by design or by oversight, is that, since typical shelter scanners stop scanning after finding one chip,[Note 7] and "Which one" can't be predicted, all of an animal's chip numbers need to be kept on file and address-updated with an appropriate database keeper for life. Presumably Banfield's enrollment forms had a space for "second chip number." The on-line enrollment forms of most registries could use some improvement in this regard. For best protection, the owner of multi-chipped pet may want to have each chip separately enrolled in its most customary or manufacturer-provided registry.

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 8] 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[17] NR OK NR NR
AVID Deluxe U.S. Scanner NR OK OK NR
AVID Universal Scanner sold outside U.S.[18] OK OK OK NR Assumed
AVID MiniTracker Pro Scanner announced August 2008[19] 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. Vet's scanner pre-2007


Trovan LID-560-MULTI per mfr. specs on Web[21] OK OK OK OK
U.S. Trovan Pocket Scanner per AKC-CAR Web Site[22] DO OK OK OK
U.S. Trovan ProScan700 per AKC-CAR Web Site[23] OK OK OK OK
Original 2006 Datamars Black Label Scanner[24] OK OK OK OK but Reliability Questioned
Datamars Black Label Scanner "classypets" model[25] 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[26] OK NR NR NR
Typical Homemade Scanner[27] 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[28] 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 tumors at the site of implantation have been reported in laboratory mice and rats.[29] Noted veterinary associations[30] 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[31]

See also


  1. ^ For display, typically three digits of country/manufacturer code are prefixed to twelve digits of the 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 would be obvious and surmountable to someone having a specimen of the "FECAVA" chips and trying to make a scanner for them, to the extent that the Annex is still quite useful to him. (The actual "FECAVA" chip's frequency-modulated signals are completely backwards/inverted from what the Annex calls for.)
  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 a lot of specimen chips; upgrades may be available, especially to current customer partners of HomeAgain.
  7. ^ It might be argued that Shelter-Grade scanners shouldn't do this.
  8. ^ 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. ^ Microchip Implantation Sites (World Small Animal Veterinary Association).
  2. ^ WSAVA - Australian Microchip Standard
  3. ^ Entering Japan: Dogs & Cats.
  4. ^ Masters, Catherine (25 March 2006). "The year of the dog war". The New Zealand Herald. http://www.nzherald.co.nz/topic/story.cfm?c_id=195&objectid=10374370. Retrieved 25 October 2011. 
  5. ^ Farm Dogs Exempted from Microchipping
  6. ^ Pet's Death Rekindles Electronic ID Debate in JAVMA News.
  7. ^ Trovan Chips Adopted by Los Angeles in 1996.
  8. ^ http://www.rfidnews.com/avidopenletter.html
  9. ^ "B" Country List (Search for "Home Again microchips are ISO compatible" in the text.)
  10. ^ ISO Standards Discussion (Search for "as compliant" in the text.)
  11. ^ The TRAVELchip Single (Search for "Complies with" in the text.)
  12. ^ ISO Standards Combined Text ("FECAVA" discussion starts on page 16 of the PDF file.)
  13. ^ Pet's Death Rekindles Electronic ID Debate in JAVMA News (Search for "best" in the text.)
  14. ^ APHIS Comment Submission from Digital Angel Corp (page 2, item 4 in the referenced .doc file.)
  15. ^ Avid Announces New Scanner to Reunite More Lost Pets with Their Families.
  16. ^ 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 (0.125 megahertz) codes "C5S" and "HS9250L"; for a recent AVID scanner, operating at 134.2 kHz (0.1342 megahertz), codes "IOL" and "-134-AV1034I" .)
  17. ^ Descriptions of AVID Scanners (Search for "only the AVID" in the text.)
  18. ^ Test Results from American Humane (Search for "in use in canada" in the text.)
  19. ^ Avid Announces New Scanner.
  20. ^ Test Results from American Humane (Search for "unless vet is with a shelter" in the text.)
  21. ^ Trovan Multi Scanner specs (Apparently applies to models sold outside U.S.)
  22. ^ Using The AKC-CAR Multi-System Pocket Scanner (U.S. Model says "Detect Only" on ISO chip type.)
  23. ^ AKC CAR Scanners
  24. ^ Datamars Multi Scanner specs.
  25. ^ Datamars Multi Scanner specs.
  26. ^ Datamars Scanner Descriptions.
  27. ^ Software for Homemade Scanners- Chip Type Listing.
  28. ^ Nov. 2007 Scanner Evaluation from EID Limited.
  29. ^ Lewan, Todd. "Chip Implants Linked to Animal Tumors". The Washington Post. http://www.washingtonpost.com/wp-dyn/content/article/2007/09/08/AR2007090800997_pf.html. Retrieved 12 May 2010. 
  30. ^ Position Statement from World Small Animal Veterinary Association.
  31. ^ "Evaluation of veterinary radiofrequency identification devices at 1T". Veterinary Radiology and Ultrasound. doi:10.1111/j.1740-8261.2010.01762.x. 

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