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homefamily pet handoutsintroduction of a new pet (to existing pets)


When you first bring home a new pet, s/he should be kept totally separate from the resident animals except when working on the gradual introduction. To begin, the new pet should be placed on the opposite side of the room from the other pets while being fed or petted. Doing this teaches the animals to connect the good things in life with the other animal. It is crucial that the animals do not react violently to each other for this to be successful. Watch for changes in facial expression, posture or vocalization as a clue that any of the animals are upset. If the negative signs either do not decrease within 5-10 minutes, or dramatically increase, increase the distance between the pets. If the animal who has been upset calms and becomes quiet, reward this within the first 30-60 seconds of the change in behavior. Pet him/her, tell her she’s wonderful, and/or give tiny food treats

Gradually, over a period of weeks, the animals should be moved closer to each other during feeding time. Once you are able to have them eating next to each other, you can allow them to spend time together while supervised. The animals can be leashed and secured at a distance from each other, and rewarded with praise and food treats when they are calm in each other’s presence. Both pets should receive equal attention, both alone and in each other’s presence. Make sure there are adequate toys, sleeping areas and (for cats) litter boxes, to lessen the chance of competition for these items.

Until the pets either cease to react to each other at all, or react favorably, they should be separated when unsupervised. Be sure to rotate the areas in which they are confined; you do not want the original pet to feel s/he has banished the newcomer to the bathroom forever, enabling him/her to maintain free reign! If the new pet is a young puppy, you may wish to crate it. Please remember that this does not afford total protection from willful fangs and claws.

The key to this is patience. If the animals are allowed to become hostile or nervous in each other’s presence, that state of mind will be reinforced. Remember, work up to this as gradually as possible; moving too abruptly could ruin all that has been achieved, and you will have to start from the beginning.

This method is also successful for animals which have lived together for some time, but have recently developed problems with each other. The pet who is a victim of aggressive behavior should be fed, walked and given attention before the aggressor; this is to reinforce the pet with less status in the household. Only allow the animals together when supervised. When separated, the aggressor should be confined in a more restrictive setting, while the other pet is given free reign of the house.

During the periods of reintroduction, watch closely for any signs of hostility, such as flattened ears, growling, hissing or staring. Within the first 30-60 seconds of the initiation of aggressive behavior, use a foghorn or a battery-operated water pistol to negatively reinforce the pet for that behavior. If the aggression persists, place the perpetrator in a neutral room for approximately 15 minutes. This deprivation of human contact further emphasizes that the aggressive behavior is unacceptable. When the pet is quiet and calm, s/he may be allowed to rejoin the owners and other animal(s).

If the aggressor continues to react unfavorably to the other pet despite the use of these methods, a flooding technique can be used. The pet who initiates the aggression is placed in a wire shallow crate in a room in which the other pet has free reign. This forces the aggressor to acknowledge the other animal’s right to exist in the household. While stressful for both animals involved, this method may hasten the resolution of the problem.

Pharmacological intervention may be required in conjunction with the described behavior modification techniques. In extreme cases of inter-animal aggression, the only solution may be to place one of the pets in a new home.

(Behavior Clinic – VHUP: Overall, Schulman, Trammell, 1990)

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