A normally energetic cat becomes lethargic. A puppy who usually eats like a pig suddenly loses his appetite. Big or sudden changes in behavior could mean something else is going on—like an underlying medical issue.
“Usually when we talk about medical roots for behavior is when we see a change,” says Lindsay Lieberman, behavior and training coordinator at San Diego Humane Society’s Oceanside Campus. The most common sign of a possible medical issue is when cats pee outside their litter box or housetrained dogs urinate indoors, she says. That could indicate a urinary tract infection.
Other behaviors to watch for are changes in energy levels or appetite, over-grooming, and excessive paw licking. But exactly what that indicates can range from something minor, like an allergy or irritation, to a problem in their environment or something uncommon like obsessive-compulsive disorder. Even aggression can sometimes be caused by a medical issue, such as arthritis. Don’t jump to conclusions, but sudden changes in behavior are definitely worth consulting your vet. (Pets adopted from SDHS get a free vet checkup.)
One behavior not to worry too much about is a lack of appetite the first couple of days your new shelter pet is in their new home. Some animals are better than others at dealing with stress. “All they know is that they’re experiencing one more change in their life,” Lieberman says. It’s worth mentioning to your vet if it persists for longer than a couple days.