CHICAGO—To the casual eye, Tippy might appear to be a regular Labrador. He loves sunbathing at the park, watching squirrels, and getting loads of attention from passersby.

Tippy and Katherine Mathers enjoy a day at the park.

But Tippy is not a normal dog. By veterinarians' standards, he is 65 pounds overweight.

A closer examination of Tippy's body reveals a rounded abdomen, thick limbs, and a fleshy neck and back. And, unlike dogs seen on television and in magazines, Tippy does not have a discernible waistline or ribcage.

"I don't care if people say he's chubby," said Tippy's owner Katherine Mathers, gently scratching the dog's protruding belly. "So what if he doesn't look like the dog in the Iams commercial? What's more important: having a perfect body or being happy? I love him whether he's 25, 50, or even 150 pounds overweight. In fact, I think he's the cutest dog in the world."

"Yes, you are!" said Mathers, waving the remaining half of her cookie in front of Tippy's nose.

Mathers is not alone in defending her pet. Amid a barrage of commercials for new diet dog and cat foods, many owners say that their pets are being held to impossibly high animal-body standards perpetrated by the media.

"I don't care what anyone says, my Sassy looks good," said Janice Guswhite, owner of a Persian longhair that cannot climb the stairs to her home's second floor without becoming short of breath. "Who's to say how big a cat is supposed to be, anyway?"

The American Veterinary Medical Association is trying. The organization recently announced that nearly one-fourth of all U.S. cats and dogs are overweight. While many owners say they are comfortable with their pets' extra weight, the AVMA says ignoring pet obesity could have dire health consequences.

"Many pet owners might think it's cute when Sparky lies next to his food bowl all day because he doesn't have the energy to walk away from it," said Dr. Ken Janokovski, spokesman for the AVMA. "But overweight animals are susceptible to diabetes, heart disease, arthritis, pancreatitis, and a host of other illnesses."

"By simply lowering the number of times you fill the food bowl, and providing enough space to exercise, you can dramatically increase your pet's quality of life," Janokovski said. "Pets are part of your family. You should treat them accordingly."

In spite of the possible health risks, many owners of so-called obese pets insist that a few extra pounds can't hurt their dogs, cats, or guinea pigs.

"Animals know how and when to eat by instinct," said Travis Linsom, owner of a clinically overweight hamster. "Oscar only eats what he needs, then keeps the rest in his pouch while he sleeps in the corner all day. That's just how hamsters are. I'm not going to force Oscar to get on the wheel just because some vet is freaking out about hypoglycemia."

Pet body-image activist Miriam Grimer said owners shouldn't let doctors dictate their pets' weight.

"It's insulting that 'experts' are telling our pets how to live," Grimer said. "Our pets are perfectly fine with the way they look. No animal should be forced to live up to the unobtainable standard of beauty on the cover of a magazine like Cat Fancy."

Preferring terms like "plump," "stout," and "curvy," Eric Willis said he's proud that his 110-pound golden retriever has "a little something on the hindquarters."

"Jasmine might not be able to run as fast as other dogs, but when I take her to the park, you can bet she gets noticed by the male dogs," Willis said. "Not like Clementine, that skinny little English pointer down the block. Her owner must not care about her at all. "

Pet owners like Willis say they have no intention of changing their feeding habits.

"No one's going to tell me that Tippy isn't beautiful the way he is," Mathers said. "If he wants to lose weight, that's fine. But he doesn't have to do it for me, or the vet, or even my husband, who doesn't want Tippy allowed in the living room because of his intestinal troubles. I think Tippy's perfect, even if he can't fit through his doggy door anymore."