Microchip in pet may have a down side

Microchipping is sort of the pet world's equivalent of Mom and apple pie &

what's not to like?

Chipping promises to eliminate that sad refrain of "where, oh, where has my little dog gone?" The rice-grain-sized implants, usually inserted in the neck-shoulder area, transmit a unique ID number, which can then be traced to the owner's contact information. The chips are detected by hand-held scanners, which are becoming increasingly available at veterinary offices and animal shelters. Some diligent breeders &

as well as some commercial mass-producers, or "puppy mills" &

now routinely chip their puppies before they go to their new homes, so they can always be traced back to them in case of theft, loss or abandonment.

Until recently, the biggest concern over microchips was migration: There was some concern that the chips might inadvertently "travel" from the site of injection, making them harder to find and scan.

But then came news reports earlier this month that pointed to studies of lab mice and rats that had developed malignant tumors near or around the implanted chips.

Published in veterinary and toxicology journals, the findings are at least a reason for pause: A 1998 study of 177 mice reported an incidence of cancer of just over 10 percent. A French study in 2006 noted tumors in 4.1 percent of 1,260 microchipped mice. And a German study in 1997 linked cancer to microchips in — percent of 4,279 mice.

None of the studies had control groups of non-chipped mice, which means that there were no "normal" cancer rates to use as a comparison.

Many veterinary oncologists are on the fence about the cancer-chip connection: Although there have been no discernible increases of neck sarcomas in microchipped dogs, there are also no long-term studies of the effect of implantation.

No one disputes the importance of having a permanent identification on a companion animal: Collars and tags can and do get damaged, and a "nude" dog or cat is basically unidentifiable.

With dogs, at least, tattooing is one alternative.

The process is simple enough: The dog is placed on its side, usually with owners or helpers holding the feet and head. After the tattoo area &

ideally, the inner thigh &

is shaved, disinfected and coated with Vaseline, the tattoo number is applied.

"What I like about it is it's absolutely permanent," says Michel Berner of Fairchild, Wisc., who is a certified tattooist with Tattoo-A-Pet International, one of several tattoo registries. "It is indisputable proof that you own the dog, just like microchipping. And I've never seen any adverse effects, like an infection or reaction."

Berner says it takes about 10 minutes to tattoo a 10-digit AKC number on the average dog, no anesthesia required. While some people use their phone number as an ID, that's not advisable, as it can change. Tattoo registries are also an option, though there is no one central database.

In coated or hairy breeds, thigh tattoos aren't very practical, unless the area is shaved constantly. As an alternative, the inner ear can be tattooed, which is routinely done with racing greyhounds.

Berner admits there's not much of a call for animal tattooers. She knows of only three or four in her state, and, other than her own litters (she breeds Vizslas), she tattoos only about 20 dogs a year. Most compete in dog shows or field trials, where the tattooing tradition is still relatively strong. And while you can request a microchip at your vet's office, tattooing is something you need to seek out aggressively. (Berner recommends contacting a tattoo registry such as or to get the name of a tattooist near you.)

If tattooing is impractical for you or your dog, should you not microchip? While the medical jury is still out, the pragmatists point to the importance of having a mechanism to help return a lost animal to its owner.

"You can treat most cancers," wrote a dog enthusiast in a recent online debate about microchipping. "You can't treat a no-kill shelter's last-day policy."

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