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Ask a Vet: Does a Microchip Prove Ownership of a Cat?

Legally the answer is clear -- no -- but pet owners and vets argue a lot over the issue.

Dr. Eric Barchas  |  Nov 24th 2015


I recently asked the veterinary technicians who work at my office to take X-rays of a cat who had been coughing. The X-rays were compatible with feline asthma.

There also was an incidental finding.

Microchips show up on X-rays as bright white structures that look like rice grains embedded underneath the skin between the shoulders above the chest. They regularly show up in chest radiographs. Two such structures were visible on the X-rays of the cat with asthma. The cat had been microchipped twice.

Double microchipping is quite common. I estimate that I see two microchips in a patient’s X-rays at least once a month. In most cases, both chips are fully functional. A second chip may be placed by a veterinarian or shelter who fails to scan the cat before placing it, or who uses a scanner that is not compatible with the first chip.

Double microchipped cats add a twist to a controversy that has surrounded microchips from the start.

What, exactly, does a microchip prove?

Most people assume that a microchip provides definitive proof of ownership of a cat. But if that were the case, who would own the cat if there were two microchips registered to different people?

Several controversies and scandals surrounding microchips have arisen over time. When microchips were first released, some people fervently opposed them because they were afraid that pet microchipping was a first step toward human microchipping and universal government surveillance. I suspect those same people have GPS-enabled cell phones in their pockets right now. For the purpose of government surveillance, microchips are unnecessary and obsolete. That controversy is dead.

Later, a study found a link between microchips and cancer. A furor ensued. However, it was unfounded — it turns out that the link has been proven only in mice that were genetically engineered to be predisposed to cancer. Things are largely quiet on the microchip/cancer front.

Another controversy is well known to veterinarians but not among members of the public. I’m referring to market share wars among companies using competing proprietary technology. For many years most microchip scanners could not read all microchips, potentially leading to euthanasias in shelters who could not identify owners. However, universal chip readers are now available and in wide use. This unnecessary and profit-driven controversy thankfully is largely behind us.

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Business people and money by Shutterstock.

For years, many shelters and humane societies were not scanning stray animals who came through their doors. This shocking scandal has abated as scanning has become the norm (and often is required by law) at shelters across the U.S.

That just leaves one major, simmering controversy.

Does a microchip prove ownership of a pet?

There are two sides to the argument. One side cites the obvious: If a person microchips his pet and registers the chip, he is the likely owner.

The other side counters that things often go wrong in the process. Some cats have two chips that might be registered to different people. Also, the person or organization that registers a microchip often turns out not to be the owner.

For instance, many pets are chipped at shelters. The chips may initially be registered to the shelter. If a person adopts the cat and fails to update the registration he is still the owner, even though the microchip says otherwise.

Other cats might change owners when they are sold, given away, or abandoned. The new owner might fail to update the chip registration.

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Adoptapalooza 2015 by Shutterstock.

And, incredibly, some people might engage in malicious behavior involving microchips. I know of a case in which a vindictive person gave her pet to a friend. The friend did not update the microchip’s registration. The friendship fell apart, and the original (former) owner contacted the microchip company in order to falsely report the pet as stolen. I also have heard of microchip registration abuse during feline custody disputes among divorcing couples.

When it comes to the subject of what microchips prove, there is no shortage of arguing that goes on in veterinary circles. However, from a legal standpoint, things are relatively clear. The Veterinary Information Network’s in-house attorney, Raphael Moore, has stated it unequivocally: In the eyes of the law, microchip registration is nothing more than product registration with a marketing company. On its own it proves nothing. However, it, along with other evidence such as receipts for pet licenses and veterinary bills, can be used in a court proceeding to help establish ownership.

Therefore, in the long run your cat’s microchip might help you if you find yourself in an ownership dispute. And it definitely should help if your cat gets lost and is taken to a vet or shelter by a good Samaritan.

But don’t expect a vet to seize a cat if the cat’s microchip is registered to someone else. Even if a microchip did definitively prove ownership, by law vets can’t seize pets.

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