The following technique can be used to introduce a new kitten or cat to your other cat(s). I’ve been involved in pet rescue most of my life and this technique worked successfully every time. Over the years I’ve had to make a few modifications when introducing older males or feral cats, but in most cases this will work exactly as outlined. It’s assumed your pet is neutered and the new pet is either neutered or less than six months old.
If you have a choice you may want to follow a “wives tale” recommendation and pick a young new cat that is the opposite sex of your pet. For example if you have a neutered male select a female kitten or young female. If you have an older female, select a young male kitten. Many people believe these combinations are the best choices to insure a compatible match. There is some biological support for this argument, but I’ve merged many same sex, same age cats and it’s always been successful.
1. Before you bring a new kitten or cat home, make sure it is free of communicable diseases-Feline Leukemia, Distemper, Rabies, worms, and fleas. Most people avoid adopting a cat that has been exposed to Feline Aides, but there’s a mixed jury on how Feline Aides is spread. You may want to read about this topic and form your own opinion before you consider merging a cat exposed to FIV with a healthy cat.
2. While the cats are still in separate locations feed them both a large meal. For example, give both cats a meal that would be comparable to our thanksgiving dinner; choices include their favorite canned food, sardines, tuna, or chicken. Give them at least an extra half serving. You may also want to give a little natural herb relaxant such as “Rescue Remedy”.
3. Place the new cat or kitten inside a cat carrier approximately a half hour after the cats finish eating their large meal. Have a friend bring the new cat or kitten into your house and place the carrier in the middle of a living room floor-make sure there is a place where the new cat will be able to hide once it’s released from the cage (i.e. a sofa, chair, etc.). If you can’t find a friend, to bring in the carrier you can do this yourself, but you must ignore the new cat at all times.
4. Let your cats smell and hiss at each other with your cat running loose in your house and the new cat safe inside the carrier. Since both cats are full and relaxed-it may take 20-30 minutes before the cats notice each other.
5. One hour after you bring the new cat inside open the carrier door, but ignore both cats. Let the new cat come out as it feels ready, this may take up to 30 minutes. The cats may continue to hiss and scream at each other, but usually it’s pretty minimal. Most often the new cat will look for a safe place to hide such as under a sofa or chair. If the new cat runs to you, ignore it.
6. For the next 3-4 days, you must ignore the new cat. Allow your cats to scream and hiss at each other as much as they need to. This let’s your current pet and the new pet establish their own pecking order. The only time you want to interfere would be if the cats got in a bad fight. If this occurs throw a large amount of cold water on both cats, and start the process over. (One time I had to merge two older sickly male cats. They had both been “Tom” cats for years. After this one hour merger technique they got in a horrible fight. I broke up the fight with water, got a large dog crate and for two days I rotated which cat was in the cage and which cat got to be loose. At the end of two days, these cats got along great.)
A final thought, you may want to start the introduction at a time when you can be home for a few days. For example, if you work Monday through Friday, you may want to merge the cats on Friday night so you can observe them over the weekend.