Patience is the key to success in pet introductions.
Several short introductions (5 – 10 minutes) after a few days of acclimation to the new home are best.
Confine one or both cats and then swap spaces for a little while to get them used to each other’s scents. If one cat is to be confined, it should be the new cat. Rubbing one cat with a towel, and then rubbing the other with the same towel is another way to get them used to each other’s scents. This needs to be done at minimum daily. One rub of the towel won’t do it.
Make sure that whatever space is used for confinement is comfortable, and has all that kitty needs. It is also probably not a good idea to confine the new cat in the resident cat’s favorite territory. For example if your resident cat spends all day and half the night in your bedroom, put the new cat in the bathroom, or a spare room.
Another trick, especially in the early introductory phase, is to put the new cat in a carrier, and let them sniff each other.
Never leave new pets alone with each other. Always supervise the interactions until you are sure they are getting along.
Introductions are best done during meal or treat times so that there is a positive association with the newcomer. Use food treats to reward good behavior, but do not “punish” bad behavior. If growling and aggression occur, go back to the previous step for a few days, and then try again.
Hissing is usually okay, as long as it doesn’t progress to growling. It usually means back off, I need more space.
Be sure to spend quality time with the resident cat. There is a tendency to want to spend a lot of time with the new cat, but the old cat needs reassurance that he or she is not being replaced.
If a fight should break out, be very careful. Pet guardians (doesn’t that sound better than “owner”) have been bitten while trying to separate fighting cats. Use a broom to get between them, or throw a towel or water over them. A wet floor is better than a trip to the emergency room for you, and a trip to the vet for the cats.
After they have calmed down, examine each one to be sure there are no bite wounds or severe scratches. Sometimes if cats are having a very hard time adjusting, your vet may prescribe medication or herbal remedies to calm them during this acclimation period. Also, a product called “Feliway”, which is a spray with natural pheromones can have a calming influence on the cats.
Again remember that patience is the key. It may take weeks or even months for cats to acclimate to each other. For some lucky souls, the cats will get along right from the start. However, most of us need to work at getting our feline friends comfortable with each other. Some cats will never like each other, but most will come to a state of peaceful coexistence if they are allowed to acclimate in their own time and their own way.