Merging pets when moving in together usually has a happy ending, but it can take time, patience, medication (for the pet) or the help of an animal trainer or behaviorist, said Dr. Chessie Green, who heads the North Carolina Veterinary Medical Association in Raleigh, N.C.
"It goes pretty well for probably eight out of 10 of my clients who blend their families," she said. "Most people don't consider their pets before moving in."
Making it work involves many variables. But Valarie Tynes, a veterinarian and behaviorist in Sweetwater, Texas, has one key observation: "A cat or a dog that has not spent much, if any, time around other dogs and/or cats during their adolescence will be much less likely to ever get along well with other animals."
Getting two adult cats to live in peace can take longer and pose greater challenges than blending dogs, Tynes said. "It's very important that people realize that some cats and cat/dog combinations may never work great," she said.
When putting dogs together, Green suggests introducing them on neutral territory first, using leashes. "Do it in a neighbor's yard or the park or a friend's house, where the dogs don't have a stake." Don't convey your own anxiety by holding the leashes too tight. "Dogs can read that," Green said.
Let them sniff each other and investigate, and pay attention to their body language. Are their ears down or back, indicating anxiety, fear or aggression? Are their tails up or down? Down might mean they're feeling anxious or scared; up signals confidence. A tail straight out can mean either neutral feelings or aggression, Green said.
Barking is okay. "It's just another means of communication for dogs. They may even growl or snarl at each other a little bit, and that's okay initially because it's establishing who's dominant and who's submissive."
What happens on neutral ground may or may not carry over to cohabitation, Green said, noting that some breeds are more territorial than others. "You might have to do it all over again" when you get home, she said.
Providing separate spaces at first is a good idea. That can mean giving dogs their own rooms or crates, especially when nobody is home. Make sure to reward good behavior and set up separate feeding stations to avoid conflict, Green said.
But if a truly bad situation doesn't improve over time — it could take six weeks or longer — and health issues have been ruled out, an animal behaviorist should be consulted, Green said.