Description: When two cats in a household become aggressive toward each other, the cause is generally fear related. The cats do not seek each other out, but if they run into each other, both are startled and will attack. Usually this problem begins by accident. For example, two friendly cats may be resting when a frightening incident occurs, such as a bookshelf falling over. Both cats become startled, puff up, and assume defensive postures. When they see each other in a defensive posture, they respond as if the other is about to attack. Thereafter they are aggressive whenever they see each other.
Solution: This type of aggressive behavior is usually treated successfully. The cats must become used to each other again without either cat becoming afraid or aggressive. First, the cats should be separated so that they cannot see each other except during treatment procedures.
One way to reintroduce the cats is when they are hungry. The cats can be positioned at opposite ends of the room several times a day and fed small amounts of food. If both cats are hungry and occupied with eating they will see each other in an unaggressive state. Bring the food dishes closer together gradually over several days or weeks. Eventually after eating, the cats can spend some time with each other if they are kept apart on leashes at a safe distance. Pet or play with the cats to keep them relaxed and in a good mood. This technique is more likely to work if the level of aggression is relatively low. If the cats' behavior does not improve using this method, the following technique can be tried.
Expose the cats to each other for prolonged periods without letting them come in direct contact. They might be kept in large cages at opposite ends of the room, where they can see each other but cannot escape. After several hours, they might be brought closer together. After many sessions, it should be possible for them to be close to each other and eventually be let loose.
Sometimes, however, a cat's defensive behavior is so intense that even the very sight of the other cat will lead to an aggressive fear response. In that case, it may be necessary to gradually bring the cats into view of each other. For example, cats could be allowed to see each other through the crack of a fastened door (opened about an inch) or through the gap below the door. Limited visual presentations can reduce the fear enough that subsequent progress can be made. The door can be gradually opened wider as the cats are fed, played with or petted.
In some cases, the cats can be separated by a screen door, with the lower screen covered completely with a large piece of cardboard. First, the cats should be allowed to approach the screen door and encouraged to play with each other's paws at the under the door. Then, a very small gap or slit can be made in the cardboard so that they can barely see each other. The play under the door should be allowed for several days. Very gradually (every few days or so), the opening in the cardboard should be widened so that the cats can see more of each other. Once they can see each other completely and still play (several weeks at least and maybe even several months), it is safe to let them play with the screen door removed.