All pet owners want their cats or dogs to be bright-eyed and frisky forever. But the fact is, by the time an animal is 6, it has hit middle age – even earlier for large breeds of dogs – and the downward slide has begun. And with that decline come additional challenges for an owner.

Dr. Michael Flaherty, the chief veterinarian at PAWS Chicago, who also has a private practice in Glen Ellyn, Ill., says there are some things pet owners should watch for. Some problems, such as decreasing mobility because of arthritis, are obvious. But others might not be.

“Kidney disease is common in both dogs and cats as they get older,” Flaherty says. “Usually the first sign is an animal drinking a lot and urinating more frequently. Bad breath; they may be getting periodontal disease. Often it’s a sign there are other things going on. Heart disease is common in older animals, so shortness of breath is one thing we kind of look for.”

What can an owner do to forestall the effects of aging?

“Keeping them thin is important,” Flaherty says. “I usually talk to people when they bring animals in earlier in life. I forewarn them to keep them thin. A lot of problems later in life are lessened because they’re not carrying that extra weight. Dogs tend not to blow knees out or develop hip problems if they’re thinner.”

Keep animals active. For a dog, take them on walks (be sure to have the pet checked out first to make sure he’s up to it). Cats are a little more difficult.

“Flashlights and feather toys,” Flaherty says. “And a lot of people play with those little laser pointers. Even the older guys still have that prey drive and like to chase things. Get them to run around.”

Diet is also important. The premium foods and supplements offered at most pet shops really do work.

“Some of the prescription diets and senior diets have lower levels of salt and sodium in them, and they often have a higher quality of protein that’s easier for the kidneys to excrete,” Flaherty says.

And don’t be a stranger at the vet. Visit twice a year.

“Six months to a dog is like roughly three to five years for a person. Especially as they get older, they can age quickly in a six-month period.”