Dog breeds

The blood test identifies genes from a base of 157 breeds, according to the Web site of Mars Inc., the company that offers the test through vets' offices. It costs about $200 but includes a veterinary appointment for reviewing the results.

Smith advocates for the blood-work test not only because it accesses more breeds but because, depending on the DNA results, some dog owners may need follow-up counseling.

"Some people might've been happy with what they thought they had, then something like 'Rottweiler' shows up," said Smith. "All of a sudden, they're looking at their dog through a completely different pair of eyes."

A veterinarian can reassure owners that "the dog you now have more information about is the dog you still love," she said.

Theresa Brady, a MetaMorphix marketing representative in Calverton, Md., said the two DNA tests are equally effective, even though her company's cheek-swab method tests for fewer breeds.

"DNA is DNA," she said. "The sampling method doesn't make a difference."

Smith and other vets caution that the DNA tests are "for fun and entertainment" — not for diagnostic purposes.

"It's just a test for owners," said vet Kelly Best of Arvada Flats Veterinary Hospital, in Colorado. "I don't know that it has any medical benefits at all."

Even for purebreds predisposed to certain diseases, their genetic dilution in a mutt makes concern about the diseases negligible, she said.

And no one has come knocking on her door asking for the test.

Smith, however, has run the blood test on many dogs.

"It's like Christmas day when (clients) get to open their results," she said. "A lot of times people are right, and a lot of times they're wrong."