Jeanette Potter

Jeanette Potter, left, a veterinary technician, and Eric Pihl hold Bonnie, Pihl's shepherd mix, during a free swim before beginning her exercise on the underwater treadmill at TheraPET in Buffalo Grove. (Andrew A. Nelles/For the Chicago Tribune)

Even before Eric Pihl pulls into TheraPET Wellness Center parking lot, his dog, Bonnie, climbs up from her lounging position in the back seat and eagerly looks out the window.

If only we all could get that excited about climbing on the treadmill to lose weight.

Bonnie, a 5-year-old shepherd mix, needs to shed some pounds — and she's one in a growing number of big dogs and fat cats, experts say.

She already has dropped a few pounds since weighing in at 63, but Pihl and her veterinarian would like her to get down to 45 or 50. So after work on Thursdays, Pihl drives her to TheraPET in Buffalo Grove to get on the treadmill. The rest of the week, they take walks together through their Arlington Heights neighborhood.

Just like humans, pets are getting fatter. Fifty-four percent of dogs and cats are overweight or obese, reports the Association for Pet Obesity Prevention. The most common side effects are osteoarthritis; insulin resistance and Type 2 diabetes, primarily in cats; high blood pressure; heart and respiratory diseases; and joint problems.

Bonnie had surgery on one knee and might have to have another operated on, Pihl said.

But he hopes her weekly run on the underwater treadmill will help her shed weight and lessen some of the pressure on her joints. He also put her on a diet, cutting her commercial dog food intake in half and replacing it with filling, high-fiber green beans. She also gets dry Rice Chex as an occasional treat, and her dinner includes a 20-calorie chicken strip.

Vets suggest that dog owners replace treats with healthier selections such as carrots, celery sticks, low-sodium green beans and frozen yogurt. Bonnie doesn't mind the beans, "but only if they're cooked," said Pihl. "I tell her that if she ever runs away, she will have to learn how to build a fire."

Jeanette Potter, a veterinary technician at TheraPET, said 9 out of 10 dogs that come through the door are overweight.

"Bad hips, bad elbows, bad knees," she said. "And a lot of it has to do with being overweight."

Although cases like Bonnie's are complicated by thyroid problems, most pets can blame their best friend for their weight issues, experts say.

Pet owners become complacent, get busy and stop walking their dogs, reward them with fattening treats, equate food with love and maybe figure their cats prefer to sleep all the time.

Try a laser pointer to get your cat up and moving, suggests Maria Manrique, a veterinarian at the South Loop Animal Hospital who made a YouTube video about pet obesity for the American Veterinary Association.

"I have seen quite a bit of an increase in weight problems," she said.

Owners often insist they are only feeding a cup of food at meals, but the cup isn't a measuring cup. "It can be a Big Gulp cup, and they are not mentioning the treat here, rawhide bone there, or the table food," Manrique said.

"Feed only for meals, as opposed to leaving the food out. No table scraps. Give small treats cut into bits if you must give treats," she tells pet owners. "I always encouraged people to come in and get their dog weighed so they can keep track. There is no charge for weighing your pet."

Keeping a dog or cat at normal weight takes stress off joints and often eliminates the need for arthritis medications as they age, she said. "Respiratory compromise is also a big issue. Overweight animals are less able to take deep breaths, can overheat easily and have increased respiratory sounds."

Surgical anesthesia also becomes more risky as doctors have to adjust dosage for body weight, veterinarians said.

To promote awareness of pet obesity and inspire people to improve their pets' health, veterinarian John Bishop last year started a Biggest Loser competition at the Willow Grove Pet Clinic in Willowbrook. Prizes were awarded for the canine and feline patients that lost the largest percentage of body weight.