"I just brought a new cat/kitten/beagle into my home, and my old cat is freaking out and won't accept it. Help!" This is one of the most common questions I get on United Cats. Does Dear Abby answer crucial life questions like this? No. Fortunately United Cats has vast and formidable resources to focus on this problem. And note that while I refer to cats below, the same techniques can be used with dogs. Aggressive dogs are beyond the scope of my expertise though, and should consult your veterinarian or one of the sites listed below for your dog related behavioural concerns.

Unfortunately by the time most people ask the question, it's too late. The secret to introducing a new animal into an established home is to do the introduction right. Just plunking a new cat or dog on the floor and saying "Guess what Fluffy!" is almost certain to fail. Most cats are territorial and are not keen on having new animals in their territory. And some cats are genetically programmed to strike out from home and establish new territories when the next litter of kittens arrives.

The basic secret is to do it gradually with positive reinforcement the whole way. If at all possible the new animal should be confined to a separate area of the home during the break-in period. If your home is so small that this is not possible your difficulties during this period are going to be greatly magnified. Also the selection of a new animal to move in with your existing pet(s) is important, as a general rule it is easy to bring kittens into a new home. Introducing an adult cat is trickier, but can still succeed with patience.

After an area is set up for the new resident get a clean cotton rag. During the period that the animals are separated, regularly rub your existing cat with this rag. It will be used when they finally meet nose to nose so to speak. If you can handle the new cat before it is even brought home, do so. Then return home and play with or pet your existing cat. It will be able to detect the scent of the other cat, this is good. Have a brief but positive interaction with the existing cat.

Then bring your new cat into the home. Preferably in such a way that the existing cat comes into no contact whatsoever. Play with and handle the new cat, then go play with the existing cat. Then you simply want to continue this for several days, meanwhile lowering the barriers between them so to speak. At the end of several days they should be allowed to sniff each other under the bottom of a closed door.

At this point progress can be slow or fast depending on the cats and their temperament. With kittens it is usually fairly quick cause once settled the kitten is going to be desperate to interact with the other cat, and adult cats generally find kittens much less of a threat. Proceed with mutual play sessions, possibly propping the door open very slightly so the cats can see each other.

When it is time for them to meet face to face, take the rag you have been preparing, and thoroughly rub down the newcomer with it. This can be especially effective if the newcomer is a kitten. Allow them to meet face to face, however keep the first meeting brief. Reinforce the cats if they are adapting well, ignore them if they aren't. I used the rag technique on my neutered male cat when I brought two new kittens into my home. He took one sniff of the kittens when he met them (they had been in separate rooms for days) and you could practically see the light bulb go on in his head. "Why, I have kittens! I'm a dad!" Within hours they were playing together. Many thanks to Dr. Kim Tavenier DVM for this suggestion.

That about covers it. Some cats may take a long time to adjust, some cats may adjust in no time. Some cats may never fully adjust. The more gradual and positive the introduction, the better the chance of eventual success.

If you have already brought a new animal into a home and are having trouble getting them to adjust, the situation is more complicated. If you can separate them and reintroduce them as above, do so. In any case it is crucial in this situation to reinforce the positive interactions and ignore the negative ones. Do not attempt to punish the cats for fighting or growling, simply separate them and ignore them if there is a problem. It can take a much longer time to get animals to adjust if the introductions weren't made properly so to speak, but it is possible.

I also recommend consulting any or all of the sites below with your cat behaviour issues:

Petpsych.com
Feline Behavior
Cats International