Provide the new cat or kitten with its own room containing all resources: Set the new cat up in a room with a litter tray, food and water as well as a scratch post and some toys. Access to a high shelf or a shelf in a cupboard should be made available if possible, where it can hide, or be above ground level, so it can have the opportunity to climb or jump up and explore.
Install Feliway diffuser/s to promote sense of security and wellbeing to both cats. One can be installed in the bedroom of the new cat, and one in the main area of the house.
The resident cat should have several feeding stations and several places to drink. He should also have places to hide or places that are elevated for him to perch on and observe. Cats like to jump and climb, and having access to shelves or hidey holes above ground level, where they can perch and observe will also give them an added sense of security. He should also have two litter trays in different areas, preferably in a quiet location for privacy!
Use a cloth to collect odours from face and flank of each cat. (Each cat should have his own cloth, label it and keep it in a plastic bag, be careful not to mix cloths up at this point – we suggest a blue hanky and a red hanky for easy identification and no chance of static shocks!). When feeding, petting or playing with either cat, briefly present it with the opposing cat’s cloth to smell. At first they may hiss or back away, and if they do react this way, don’t pick them up or pat them, because occasionally they may transfer aggression onto you.
Eventually, after repeated presentation with the cloth the cat will eventually ignore the scent or may actually react positively to it. When both cats are acting this way, move onto the next stage.
Keep the cloths together in a bag so that the scents mix, and present the mixed scents to the cats in the same way that you did before. Once there is positive reaction to the mixed scent, rub the scents on objects that the cats will frequently smell, or rub up against, including furniture, and even yourself!
Allow the new cat to explore
Next, allow the new cat to explore the house alone, (put the resident kitty away in a room that he enjoys being in for a few hours) and find out where all resources are, and hiding places etc. This helps him to learn all the escape routes, hidey holes etc, so he will feel less vulnerable when they do meet. When he is confident, and using the resources available, it will be time to move onto the next stage. Some cats are more confident and outgoing than others, so it may take a couple of days, or a couple of weeks, depending on personality, and early experiences.
Face to Face
Now it is time to let them meet! Managed meetings must be arranged, so they can see each other without a risk of attack. Perhaps the pet carrier may work for you, or having a mesh door between them, where they can see and smell each other. If using a mesh door, rub the scents of both cats on the door before. Here you can feed them, on either side of the screen, slowly over time bringing the bowls closer together at feeding times, or distract them with a game. They will begin to associate each other with something positive, hopefully!
The key is to take it slow, it may take a week, it may even take a month or two, depending on each individual cat . A younger kitten of the opposite sex is often accepted quicker by the resident cat, than an older cat. Remember not to move onto the next stage if either cat is still showing either fear or aggression.
It is most important that there are enough resources for the cats which include “safety spots”.
The general rule is one litter tray per cat plus one extra, so in a household having two cats, you would need three litter trays, in different locations. The same goes for food and water, high hideaway holes, shelves etc etc. This is particularly important for indoor cats, where they rely totally on us to provide them with these resources. Any competition or perceived competition for resources can cause stress, which can lead to behavioural problems like aggression and urine spraying.