Animal Behavior Case of the Month

Sara L. Bennett Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.

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Statement of the Problem

A cat was evaluated because of aggression toward the other cat in the house (its littermate) for a duration of 2 years.


The patient was a 6-year-old 3.6-kg (7.9-lb) spayed female domestic longhair cat.


The patient and its littermate (a 6-year-old castrated male domestic longhair cat [weight, 6.0 kg {13.2 lb}]) had been neutered and had undergone declawing of the forefeet when they were 6 months old. The cats were strictly housed indoors and had been adopted by the owner when they were 5 months old.

The cats had started fighting 2 years prior to the behavioral evaluation. At that time, the littermate had ingested a plant and was taken to the primary care veterinarian for treatment. When it was brought home, the cat was lightly sedated and still carried the scent of the veterinary clinic. The patient attacked the littermate at that time. The owner immediately separated the cats but quickly reintroduced them. The cats were housed together but did not continue social grooming or sleeping together. The owner moved frequently; after each move, the cats began fighting. The patient was always the aggressor during fighting. Triggers for the patient's aggression included vocalization by the littermate, sniffing of an item that had the littermate's scent, or abnormal behavior of the littermate. Typically, the altercations were triggered by loud vocalization by the littermate. The patient would hiss, have piloerection, elevate the caudal aspect of its tail slightly above the ground, and place its ears to the sides. The littermate would then run away and the patient would chase. When the littermate was cornered, it would roll over and fight back. After a fight, the patient would stand in the middle of the room, maintain piloerection, and hiss. The littermate would cower and hide, with its body in a low position and ears back, until the patient left the room. Fighting of the cats had progressively increased in frequency and severity. The time required before reintroduction had increased after each fight. Eventually, the cats were separated at all times.

The patient also frequently sham sprayed. It would back up to a vertical surface, lift its tail, arch its back, and shake its tail vigorously; however, the cat never expelled urine. Triggers for this behavior included the littermate walking by, the owner moving past, and loud noises.

The cats had been housed separately for 2 months prior to the behavioral evaluation. The patient was confined in a room, and the littermate was allowed access to the rest of the house because it would vocalize excessively when confined. The cats each had a litter box, bed, food, and water in their areas. The cats were offered canned food twice per day, and dry food was available at all times.

Physical Examination Findings and Laboratory Results

Results of physical examinations of both cats at the time of the behavioral evaluation were unremarkable. Results of laboratory analyses for the cats (CBC, serum biochemical analyses, urinalysis [for the littermate only], and thyroxine [total T4] testing) performed 6 weeks prior to that time were also unremarkable.


Differential diagnoses for aggressive behavior of the patient included territorial aggression, fear aggression, and status-related aggression.1–4 Differential diagnoses for the sham spraying behavior of the patient included territorial behavior, status-related aggression, and anxiety.1,3 Differential diagnoses for the behavior of the littermate included fear aggression and status-related aggression.1–4

Territorial aggression was considered as a diagnosis for the patient because of its overt aggression and body language in response to the presence, scent, and vocalizations of the littermate.2 This was determined to be pathological aggression because the littermate was formerly included in the patient's social group.3 Also, the patient may not have recognized the littermate when it returned from the veterinary clinic after treatment for plant ingestion because of abnormal behavior and scent at that time.2 Fear aggression was considered as a diagnosis for the patient because it could have been frightened by the abnormal behavior and scent of the littermate after returning from the veterinary clinic.5 The patient's body language could have been consistent with territorial or fear aggression; fear can be a factor in territorial aggression of cats. Social conflict (status-related aggression) between the cats could have been a contributing factor to the behavior because similar altercations can occur in 2-cat groups when 1 or both of the cats reach social maturity (when they are approx 2 to 4 years old).3 Sham spraying behavior can be a covert sign of territorial behavior and is consistent with a diagnosis of territorial aggression.1,3 Social conflict6 and stress attributable to frequent moves can also increase this behavior.

Fear aggression was a likely diagnosis for the littermate's behavior toward the patient. When threatened, the cat would run away and hide in a fearful, defensive posture. When the patient followed the littermate and it could not escape, it had overt defensive aggression. This behavior is typical of fear aggression.1–4,6

The diagnosis made for the patient was territorial aggression (likely with a fear component) and sham spraying. The diagnosis determined for the littermate was fear aggression. Status-related aggression as a component of the behavior could not be ruled out.


The cats were housed separately at the time of the behavioral evaluation; the owner was asked to continue to provide adequate access to resources in separate core areas for each cat in the home. She was also encouraged to commingle each cat's scent into a common group scent in the environment by swapping the areas where cats were confined, switching their carriers, and rubbing each cat with the same towel repeatedly each day.1,2 The owner had been providing pheromone diffusersa; the recommendation was made to continue use of pheromone diffusers in the rooms where the cats were housed and the room in which reintroduction of the cats was to be performed. That producta contains the F3 fraction of feline facial pheromones, and it may have some effect in decreasing the frequency of urine spraying7 or other territorial behaviors.4

The owner was instructed to perform systematic desensitization and classical counterconditioning by means of reintroduction exercises for the cats.1,2,4 Both cats would eat a canned food treat without showing aggression or fear on opposite sides of a closed solid door. Then the cats would be in separate carriers in the same room during the next step of the desensitization and counterconditioning program. Training of the cats to enter the carriers willingly by use of food treats was discussed. The cats were to be placed in carriers, taken to a room, placed on opposite sides of the room, and each given a high-value food treat. After the cats finished the treats, their carriers were to be removed and the cats placed back in their respective areas of the house. The distance between the carriers was to be gradually decreased during several sessions until they were a few feet away. Next, this process was to be repeated with the littermate loose in the room while the patient remained in the carrier. The owner was instructed that if either cat stopped eating the treat or had signs of aggression, the training had progressed too quickly; if these signs were noticed, the procedure was to be started at an earlier step during the next session, and the training was to progress at a slower rate. In the last step of the treatment, both cats were to be loose in the room and the treats placed far apart; the treats were to be gradually moved closer together.

Body harness and leash training, performed in a manner similar to the carrier training, would have made the final step of systematic desensitization more controllable if one of the cats showed aggression. The owner did not use harnesses for the cats and was reminded to keep a heavy blanket, piece of cardboard, or open carrier nearby in case the cats needed to be quickly separated.

Pharmacological treatment had been initiated by the primary care veterinarian 5 weeks prior to the behavioral evaluation on the basis of the recommendation of the author after results of laboratory analyses were available for both cats. For the patient, fluoxetine compounded into a liquid suspension was prescribed (concentration, 4 mg/mL; dose, 1 mL, PO, once daily [1.1 mg/kg/d {0.5 mg/lb/d}]). For the littermate, alprazolam was prescribed (0.125 mg compounded into a chewable treat; dose, 1 treat, PO, q 12 h [0.02 mg/kg {0.009 mg/lb}, q 12 h]).

Fluoxetine, a selective serotonin reuptake inhibitor, was chosen for the patient for treatment of anxiety likely associated with aggression. The choice of this drug was supported by the diagnosis of territorial aggression with a likely fear component and the suspicion that the cat perceived its littermate and long-term housemate as an intruder.3 The fluoxetine dosage was slightly higher than the recommended dosage (0.5 to 1 mg/kg/d [0.23 to 0.45 mg/lb/d]).4 Alprazolam was recommended for the littermate because of concerns that its fear responses (flight or fighting) could exacerbate the patient's aggressive behavior.1 Benzodiazepines, which enhance the effects of γ-aminobutyric acid (an inhibitory neurotransmitter), have been administered to cats to decrease the likelihood of a flight response.8 Potential adverse effects of both drugs (inappetence, lethargy, increased anxiety or aggression for fluoxetine4; sedation, polyphagia, paradoxical excitation or aggression, and acute hepatic necrosis for benzodiazepines4,8,9) were discussed with the primary care veterinarian during the initial communication and with the owner during the behavioral consultation. At the time of the behavioral evaluation, the littermate had been receiving alprazolam for approximately 5 weeks, but biochemical analysis of the cat's circulating liver enzyme activities had not been repeated, despite the recommendation that this be done approximately 5 days after starting treatment.9 Repeat analysis, performed at the time of the behavioral evaluation, revealed values within the reference intervals. Lorazepam or oxazepam would have been alternative benzodiazepines for treatment of the littermate; these drugs may have lower potential for toxic effects versus other benzodiazepines4 because active intermediate metabolites are not formed in the liver.10


During the first month after the behavioral consultation, the owner followed desensitization recommendations by switching the cats’ carriers, swapping the areas in which they were housed, and rubbing cats daily with the same towel. At the end of the second month after the behavioral evaluation, the cats would eat in their carriers when they were spaced 2 feet apart. The next part of the desensitization treatment, during which 1 cat was loose and 1 was in a carrier, was performed during the subsequent 3 months; progress during this time was slowed because the owner had to sell the house and move. During that time, it was recommended to the owner to decrease the amount of canned food fed to the cats at meal times so that the cats would be more interested in eating during the reintroduction exercises.

A follow-up behavioral evaluation was performed 6 months after the initial evaluation; this was 3 weeks before the owner was to move. At that time, both cats were loose and eating treats 6 feet apart during reintroduction exercises. The cats were together for approximately 2 minutes during each session and were separated as soon as they were finished eating. Suspension of the reintroduction exercises was recommended during the move. In the new home, core areas were to be prepared for each cat, and commingling of scents was to be continued. After the owner was settled in the new home, reintroduction sessions were to be restarted with the cats farther apart than they had been during the last session performed in the former home. The owner was also instructed to allow the cats to remain together after eating for gradually increasing amounts of time. The cats were to be allowed to interact; if either cat showed increasing levels of threatening behavior that was not appropriate, the owner was to intervene, start the training at the previous step, and proceed at a slower rate.

The owner was ready to restart the reintroduction sessions 2 months after the move. After reintroduction exercises performed during the subsequent 3 months, both cats were loose and eating a few feet apart during the sessions. The owner was instructed to gradually increase the amount of supervised time during which the cats were together. A recommendation was made that both cats continue to receive medications for 3 months after successful reintroduction; then the medications were to be gradually discontinued by decreasing the doses 25% every 2 weeks.


Feliway, Ceva Animal Health, Rutherford, NJ.


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