Defusing Intercat Aggression

A client has consulted us for a solution to a growing problem of aggression between his two cats, both of which are kept exclusively indoors. The victimized cat hides most of the time, only to be attacked when it does emerge. Another problem is that one or both of the cats are not consistently using the litterbox.

A complete, thorough history is essential before any behavioral treatment plan is instituted. Cats that are not using the litterbox may have concurrent medical conditions and environmental issues with it (such as dislike for substrate and location) as well as behavioral problems. Treatment for aggression between cats living in the same household requires separation when supervision is not possible. This step is essential. The aggressor is banished to a less desirable location (e.g., spare room) while the victim is allowed free range or access to favorite locations. Reintroduction is gradual and supervised at all times, with owners vigilant during these sessions.

Stopping the StalkerThe aggressor can be fitted with a harness or collar and bells, allowing both victim and owner to hear the aggressor at all times. At the first sign of aggression-passive or active-the aggressor should be startled using the mildest stimulus necessary.¹ Passive aggression1 involves threats such as staring, lowering the head and neck, elevating the rump, piloerection of the tail and tail base, and occasionally low growling. Active aggression includes stalking, wrestling, chasing, boxing, biting, vocalizing, hissing, scratching, and piloerection.

Play or Aggression?It is often difficult for clients to differentiate between play, which includes some of the behaviors listed above, and aggression. In general, if cats are chasing each other, it is important to determine whether it is always the same cat chasing the other or if the cats alternate roles. If it is always the same cat being chased, the possibility of aggression should be considered, especially if there are concurrent house-soiling problems. When aggression is clearly a problem between cats, all such behavior should be considered undesirable and consistently treated. It is also important to provide strictly indoor cats with a stimulating environment that includes playing and searching opportunities, hiding places, and high perched resting areas.

The stimulus used to startle the aggressor is meant to interrupt and distract but not to terrify the cat, as fear can increase aggression. Just calling the cat's name is sometimes adequate. Furthermore, cats can be taught to come and sit on command. If the cat will come when called, the owners can then ask it to sit and reward it with a special food or some other treat. Following the distracting stimulus with a simple command ("come"/ "sit") and a pleasant experience enhances the effectiveness of the intervention; the cat will learn to associate coming when called with a treat or some other valued reward. It is important to note that not all cats are motivated by food; some respond better to petting, talking, playing, or other forms of attention.

Timing is ParamountThe aggressor must be interrupted at the beginning of the sequence-that is, as soon as it seems to be considering threatening the other cat. Clients need to preempt the undesirable behavior. If the threatening occurs before the owner employs the distraction, the client may inadvertently reward the aggression. The aggressor will associate the threatening behavior with the client calling and distracting him; then receiving a treat. The lesson becomes "to receive a treat, harass the other cat."

Some cats are not as easily distracted as others. It may be necessary for the owners to squirt the cat with water or to use an unusual or loud sound, such as that produced by a compressed air canister.

Making the Twain MeetGradual reintroduction for severe intercat aggression such as in the above scenario first requires establishing a distance at which the victim can see the aggressor without exhibiting fear and at which the aggressor does not threaten the victim. Clients must observe the body language of both cats to determine this initial distance. It may be useful to use two carriers for the initial reintroduction with the victim in one and the aggressor in the other. When both cats can remain calm within sight of each other, they should both be rewarded with special food treats. The victim is rewarded for not being anxious (better yet-for being relaxed), and the aggressor is rewarded for not threatening the victim. Distance between the two carriers is decreased slowly over the course of several months.

For cases of milder aggression, it may even be possible to feed the cats at a distance that allows them to see each other yet remain calm. The victim must be able to eat a normal food portion and should not hiss. Anxious individuals are often unable to eat. The aggressor must not stare or growl. It is essential that no aggressive event take place; otherwise this method will not work. The purpose of this exercise is to break the association between sight of the other cat and aggression, stress, bad situations, fear, and anxiety. Instead, a cat will learn that when the other cat is around, it will be fed or given treats.

Treating intercat aggression takes time, so patience is a necessity. It can easily take 6 or more months in cases of severe aggression before cats can be allowed to reside in the same space unsupervised, and victim and/or aggressor may require medication. Most drugs used in behavioral medicine are not labeled for use in cats. A complete blood cell count and chemistry screen should always be done before any of the drugs listed in the accompanying Table are prescribed.

My choice of medication for the victim depends on its level of anxiety. This is determined by the cat's behavior. A cat that is completely withdrawn can benefit from buspirone or clomipramine. Clomipramine is administered once daily; buspirone is given two to three times daily. The choice of medication for the aggressor depends on the severity of the aggression (e.g., passive versus active, occasional versus continuous). In general, for milder forms of aggression and/or anxiety I use clomipramine once daily; for more severe cases I use a selective serotonin-reuptake inhibitor, such as fluoxetine, once daily. I tend to start at the lower range of drug dosages, and increase if necessary 2 weeks later. Potential side effects should be considered before implementing a given treatment.

Cats have traditionally been considered to be solitary, territorial animals. Research conducted over the past two decades has demonstrated that although a cat can survive alone and must hunt alone, it can also be profoundly social. While results of treating intercat aggression may not produce amiable behavior between cats that were previously at odds, it can evoke a state of peaceful coexistence.

What to do1. Separate cats when unsupervised.2. Fit aggressor with warning bell.3. At first aggressive sign(s), startle aggressor.4. Follow interruption with reward.5. Gradually reintroduce cats.6. Reward cats for mutual tolerance.7. Provide stimulating environment (play, high perches, hiding places).

Sniffing Out the ProblemIn this case, it is likely that the victimized cat is the one failing to use the litterbox. A video camera set to record near the soiled location will confirm the culprit. The litterbox is a popular area for attacks. The treatment regimen described here should resolve both problems, although it is advisable to rule out physical and environmental causes of elimination problems at the outset.

Drugs Used for Behavioral Treatment in Cats ^1,3,4Drug DosageTricyclic AntidepressantsAmitriptyline 0.5-1 mg/kg PO(Elavil®) q 12-24 hrNortriptyline 0.5-1 mg/kg PO(Pamelor®) q 12-24 hrClomipramine 0.3-0.5 mg/kg PO(Clomicalm®) q 24 hrSelective Serotonin-Reuptake InhibitorsFluoxetine 0.5-1 mg/kg PO(Prozac®) q 24 hrParoxetine 2.5 mg/CAT PO(Paxil®) q 24 hrSertraline 0.5 mg/kg PO q 24hr(Zoloft®)BenzodiazepinesDiazepam 0.2-0.4 mg/kg PO(Valium®) q 12-24 hrOxazepam 0.2-0.5 mg/kg PO(Serax®) q 12-24 hrAzaperoneBuspirone 2.5-5 mg/CAT PO(BuSpar®) q 8-12 hr