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Basics ⬇

Basics

Definition

Intercat aggression-offensive or defensive aggression between cats consisting of staring, displacing, vocalizing (growling, yowling, shrieking), spitting, hissing, swatting, lunging, chasing/stalking, and/or biting other cats.

Pathophysiology

  • May be normal behavior or abnormal.
  • May be caused by underlying medical disease (e.g., CNS) or the indirect result of concurrent medical disease lowering the threshold for irritable responses (e.g., pain, hyperthyroid).
  • May be multiple motivations including predatory/play, disputes over territory, sexual, fear, anxiety, and redirected.

Systems Affected

  • Behavioral.
  • Skin/Exocrine-secondary to traumatic injury.
  • Immune-chronic stress may alter the immune response.
  • Secondary infection (cat bite abscesses) are not uncommon.
  • Nervous.

Genetics

No specific genetic basis, although some evidence to suggest that friendliness is mostly genetic and related to paternal effects.

Incidence/Prevalence

Unknown

Geographic Distribution

None

Signalment

Breed Predilections

None

Mean Age and Range

  • Can occur at any age when due to changes in social environment (e.g., addition of a new cat, return of a cat from the veterinarian) or redirected.
  • Previously stable cat relationships can deteriorate as cats reach social maturity (2–4 years of age).

Predominant Sex

  • Intact males more likely to initiate intercat aggression (related to territory, and/or proximity to females).
  • Females will defend their young from unfamiliar individuals.
  • Male kittens are more likely to initiate intercat aggression related to the predatory components of play.

Signs

Historical Findings

  • May arise spontaneously and vary in frequency and intensity.
  • Owners most likely to seek behavioral intervention if there are physical injuries, the welfare of the aggressor and /or victim is compromised, or fighting becomes sufficiently distressing.
  • Human intervention in an attempt to interrupt fighting may result in human-directed aggression/injury.

Aggressor (usually offensive)

  • Covert signs: staring, displacing other cats, stiff body language/movements while approaching the other cat.
  • Overt signs: Growling, yowling, spitting, hissing, swatting, lunging, chasing/stalking, and/or biting other cats, dilated pupils, may be accompanied by body language of fear (e.g., the classic Halloween cat stance-piloerection, back arched, tail up) or more offensive body language (stiff muscles, tail head elevated but rest of tail down, back straight or slightly slanted toward the head, ears forward or to the side), excessive facial marking, and perhaps urine marking.

Victim (usually defensive)

  • Covert: avoidance of aggressor, hiding, change in grooming and eating habits, hypervigilance, dilated pupils.
  • Overt: hissing, swatting, running, vocalizing (including growling), Halloween cat stance, may escalate to defensive attack if cornered.

Elimination Outside of the Litter Box

  • Aggressor may block access to the litter box area, forcing victims to choose alternative elimination locations; secondary substrate and/or location preferences and aversions can develop.
  • Both victims and aggressors may urine mark.
  • Extremely fearful cats may urinate or defecate in midst of aggressive events.

Physical Examination Findings

  • None except injury from fights or if underlying medical issues.
  • Stress may affect eating and self-grooming (increased or decreased).

Causes

  • Lack of appropriate socialization to other cats prior to 7 weeks of age.
  • May be a component of normal social behavior.
  • Social and environmental instability such as the addition of a new cat, loss of a resident cat, odor stimuli (return of a cat from the veterinarian or giving one cat a bath), aging or illness of one or both cats, cats reaching social maturity.
  • Household change, e.g., moving, changing furniture or resting areas.
  • Genetically unrelated cats and cats that have recently moved in together are more likely to show aggressive behaviors toward each other.
  • Resident cats commonly need prolonged exposure to new cats before accepting them into group.
  • Resource limitation (not enough vertical and/or horizontal space, lack of appropriate hiding areas, and limited food, water, and litter boxes, etc.) in multi-cat households.
  • Exposure to arousing stimuli (cats in the yard, visitors, noises, scents, etc.) can cause redirected aggression after which aggression might persist.
  • Medical problems including CNS disorders, hyperthyroidism, or any disorder that causes pain and/or increased irritability.

Risk Factors

  • Singleton and/or bottle-raised kittens.
  • Lack of social exposure and experience with conspecifics during the socialization period (2–7 weeks) and beyond.
  • Male intact cats in multi-cat households.
  • Postpartum females with kittens in multi-cat households.
  • Separating and returning housemate (e.g., following veterinary visit, groomer).
  • Changes in social group such as the addition of a “new” cat to a home of resident cats.
  • Scratching and biting during the first introduction risks future intercat aggression.
  • Access to the outdoors and/or intrusion of unfamiliar cats onto the territory.
  • Crowding or lack of adequate social space and access to resources (food, water, litter boxes, and resting stations).

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

Behavioral Differentials

  • Fear-related aggression-cat may hiss, spit, arch the back, display piloerection and attempt to flee unless escape is thwarted; pupil dilation will accompany a fear response.
  • Status-related aggression-may occur with change or instability of social hierarchy and the control of access to resources; it is undecided if cats have dominance hierarchies or if conflict is better explained by territorial defense.
  • Territorial aggression-in response to threat to the territory; boundaries are often delineated by marking with urine, feces, or scent glands.
  • Redirected aggression-exposure to agitating stimuli (cats in the yard, visitors, noises, scents, etc.) with aggression directed toward a target other than the agitating stimuli.
  • Failure of recognition-aggression between feline housemates after returning from separation (e.g., veterinary visit, grooming); most likely due to change in odor and visual cues of victim.
  • Maternal aggression-aggression during the periparturient period; females guard kittens and nesting sites from unfamiliar individuals.
  • Intermale aggression-between males in response to territorial disputes, hierarchical status, or mates; aggression may be more pronounced at social maturity.
  • Sexual aggression-male typical behavior of chasing, pouncing, biting on the nape of the neck, and mounting with or without intromission.
  • Predatory/play-related aggression-predatory components of play directed toward another cat; the recipient is often an older cat that is not interested in playing.

Medical Differentials

  • Any illness causing malaise, pain, or increased irritability
  • Endocrine, e.g., hyperthyroidism
  • Neurologic: space-occupying lesions, e.g., meningioma, lymphoma, encephalitis, seizures, feline ischemic encephalopathy, trauma, sensory or cognitive decline
  • Infectious: rabies, toxoplasmosis, aberrant parasitic migrations (e.g., cuterebriasis), FIV, FeLV
  • Iatrogenic: medications that increase irritability or disinhibit aggression (e.g., mirtazapine, benzodiazepines, buspirone)
  • Toxins: lead, illicit substances

CBC/Biochemistry/Urinalysis

Baseline CBC, biochemistry, urine to rule out medical causes and as a baseline if drug therapy indicated.

Other Laboratory Tests

  • FeLV/FIV
  • Cats >6 years should have total T4measured

Imaging

As indicated based on history and physical signs

Diagnostic Procedures

  • Obtain a detailed behavioral and medical history of the patients.
  • Identify if there is a clear aggressor and/or victim and if aggression is overt or covert.
  • If multiple cats determine which cats spend time together, mutually groom each other, and which cats physically avoid each other.
  • Identify the preferred core areas of each cat for feeding, play, and resting and locations of any house soiling or marking.
  • Identify: the number, location, types of litter boxes and their management.
  • Media in the form of video, photographs, and/or drawn floor plans can provide spatial details and information regarding body language during social interactions.
  • Note any other changes in demeanor, routine, eating, and grooming.

Pathologic Findings

None unless concurrent medical diseases

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Treat as outpatients with behavior and environmental modification (± medication)
  • Current on routine vaccinations, including rabies

Nursing Care

Supportive care if any injuries from fighting.

Activity

May need to be restricted if confinement required to prevent the perpetuation of aggression and negative emotional responses. Provide sufficient alternate outlets for each cat during confinement area and during release.

Diet

None (except possible therapeutic diet trial discussed below)

Client Education

For chronic, severe cases or for aggression that does not respond to treatment, may require permanent separation either by rehoming one of the cats or by splitting up the residence.

For Cases that have a Low Frequency of Intense, Injurious Aggressive Outbursts

  • Separate the cats when they cannot be supervised (create “safe zones”).
  • Either keep them separate in the same areas each day in an effort to form separate core territories for each cat, or “time share” the space between cats.
  • Confine the newly introduced cat or the aggressor to the smaller, less familiar area.
  • For multiple cats, separate by stability of relationship between cats. Any despotic/bully cats should be confined alone.
  • Consider “artificial allomarking” to form a communal scent between the cats that are fighting; a towel (facecloth) may be rubbed (cephalocaudally) to obtain the scent of one cat and then rubbed onto the other cat and vice versa.
  • Towels should be left in the environment to allow for habituation to each other's scent especially if the cats are kept separated.
  • Reward cats with food, play, and/or attention for being in the same room together without having aggressive events. Cats should stay at a distance that allows for calm participation.
  • Engage cats in daily sessions of pleasurable activities (e.g., play, training, eating delectable food treats) at distances that do not incite aggression. Gradually move the fun sessions closer to each other, making sure to stay at a distance that does not trigger overt/covert aggression.
  • Teach the cats a “come and/or go to place” cue using positive reinforcement at times, in situations, and with sufficient rewards that the cats are most able to learn.
  • Interrupt or redirect the cats by cueing to come or go to its place, or by luring one or both cats to their safe zones with food and treats, wand toys, tossed toys, or laser pointers before aggression starts or as initial signs are seen (e.g., staring, tail twitching, pupil dilation).
  • Aversives and/or punishers can increase aggressive behavior and increase negative associations with other cats, so must be avoided or used cautiously.
  • The goal of management and safety is to prevent aggressive events. In an emergency, use of a laundry basket or blanket placed between or over the cats, can stop aggression, and direct the cat to its safe area until calm, but should not be considered as a treatment.
  • Bell the aggressor (using a quick release or safety collar) so both the owners and victim can quickly identify his/her location.
  • Increase the number of resources and locations (e.g., food, water, scratching, perching, bedding, play and feeding toys) throughout the residence including each cat's core area. The efficacy of multimodal environmental enrichment should not be underestimated.
  • Increase litter boxes to the number of cats plus one divided among multiple locations so that one cat cannot keep another from accessing the boxes; locations with more than one exit/entry are ideal.
  • Increase the number of hiding places and resting areas; especially concentrate on increasing vertical space (e.g.,. resting areas on shelves, window sills).
  • No new cats should be added to the house.

For Cases where the Cats Cannot be in the Same Room without Immediately Becoming Agitated

  • Separate cats completely when unsupervised.
  • Meet each cat's needs for play, litter boxes, food, water, perching, resting, and attention.
  • A large wire dog kennel or vertical orientated wire cat cage (with shelving) may be better tolerated than smaller cat kennels and can be used for controlled exposure.
  • Cats may be taught to tolerate harnesses and leashes so that they can be used during training and controlled reintroduction. This is especially valuable for the aggressor.
  • Set up desensitization and counter-conditioning sessions daily; initially utilize physical and visual barriers.
  • Introduce the cats (in their kennels or on leash and harness) at a distance from each other that prevents overt/covert aggression. Feed the cats or engage in play for classical counterconditioning.
  • Over many sessions gradually reduce the distance between the cats, being careful to stay far enough apart during each session that no overt or covert behavioral signs of aggression and/or fear are seen. Start and end all sessions on a successful note.
  • Teach the cats a “come and/or go to place” cue using operant counterconditioning and positive reinforcement. Practice these cues several times daily so each cat learns to respond reliably. Behavioral cues are best taught when animals are not stressed.
  • When ready to allow the cats more freedom with each other, follow the instructions for less severe interact aggression (above).

Surgical Considerations

Neutering intact males is approximately 90% effective in reducing roaming, intercat aggression, and urine spraying. Neutering/spaying is effective in reducing mounting/sexual behavior.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

As all medications are extra-label, insure that the client is informed, and review target desirable outcomes and potential adverse effects.

For the Aggressor and/or Victim

Selective Serotonin Reuptake Inhibitors (SSRI)

  • Fluoxetine or paroxetine 0.5–1 mg/kg PO q24h.
  • Drugs of choice for aggression, anxiety, and/or urine marking, may decrease impulsivity.
  • Side effects may include gastrointestinal upset, decreased appetite, sedation, urinary retention (paroxetine), and increased agitation/irritability.

Tricyclic Antidepressant (TCA)

  • Clomipramine 0.3–0.5 mg/kg PO q24h: serotonin selective tricyclic: for anxiety and aggression
  • Side effects include gastrointestinal upset, sedation, urinary retention, constipation, and lowered seizure threshold. Do not use in patients with arrhythmias or cardiomyopathies.

Pheromones

Feliway and Feliway Multicat (CEVA) and Felifriend (CEVA, presently available in Europe) are feline facial pheromones that may be helpful in cases of intercat aggression when used with a multimodal plan.

For the Victim

Azapirone

Buspirone 0.5–1 mg/kg PO q8–24h (feline dose): reserved for victims to increase social confidence.

  • Side effects rare; may include decreased sociability and increased agitation/irritability. May increase intercat aggression as victim may be more confident and fight back.”

Benzodiazepines

  • Lorazepam 0.125–0.25 mg/cat PO up to q12–24h or oxazepam 0.2–0.5 mg/kg PO q12–24h for anxious or fearfully aggressive cats and as an appetite stimulant helping to facilitate classical counter conditioning. May be used as needed with peak effects seen within 1hour.
  • Side effects may include increased appetite, ataxia, inhibited learning, and disinhibition of aggression.
  • Note: controlled substance; dependence can develop; Medication should be gradually weaned if used consistently for longer than 2 weeks.

Contraindications

  • Benzodiazepines should be used cautiously or avoided in cats with hepatopathies.
  • Paroxetine and TCAs may produce anticholinergic side effects. Fluoxetine also occasionally reported to cause urine retention.
  • SSRIs and TCAs should be used with caution in patients with histories of cardiac abnormalities, seizures, and liver disease.

Precautions

  • Any behavioral drug has the potential to produce paradoxical reactions, including fear, anxiety, hyperexcitability and/or aggression.
  • Medications that alter serotonin levels have the potential to produce serotonin syndrome.

Possible Interactions

  • Avoid concurrent use of SSRIs and TCAs or MAO inhibitors such as selegiline and use cautiously or avoid with buspirone, tramadol, and tryptophan due to possible serotonin syndrome.
  • Caution with concurrent medications considered substrates of P450.

Alternative Drugs

  • Amitriptyline (TCA) 0.5–1 mg/kg PO q12–24h: for anxious cats especially if comorbid recurrent FIC/FLUTD; not selective for serotonin reuptake inhibition and likely less effective for the aggressor.
  • Dietary supplementation with alpha-casozepine (Zylkene: Veotquinol), ROYAL CANIN Veterinary Diet CALM (contains alpha-casezopine, l-tryptophan, and nicotinamide) or Hill's Prescription Diet Multicare Feline Urinary Stress (contains l-tryptophan and milk protein hydrolysate).

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Clinicians should monitor patients 2 weeks after treatment initiation and monthly for the first few months by phone or email; a follow-up visit should be scheduled 4–8 weeks into treatment if drugs dispensed to assess response and adjust dose if necessary.
  • Benzodiazepines may rarely cause cases of fatal hepatopathies; patients should be rechecked immediately if any adverse events, including anorexia.
  • Medication should be used for at least 4–6 weeks after resolution of signs, then gradually weaned by reducing the dosage no faster than 25% per day on a weekly basis.
  • Some patients require long-term medication; recheck laboratory work every 6months to 1 year depending on health and age..

Prevention/Avoidance

  • Proper socialization 2–7 weeks and ongoing. Gradual introduction more closely resembles the natural process through which new cats enter an existing group at the periphery and may be accepted over time. Intercat aggression may be more common when unfamiliar cats are suddenly placed together. A negative initial encounter is often associated with future intercat aggression. Related and familiar cats are less likely to have intense intercat aggression. In stable multi-cat households, avoid adding additional cats.

Possible Complications

Abrupt withdrawal of behavioral medications may result in aggression and rebound anxiety.

Expected Course and Prognosis

  • The prognosis for most cases is fair; it is complicated by prolonged duration, high intensity, underlying medical conditions, and incomplete owner compliance. In one study 62% (30/48) were considered cured and 37% (17/48) not cured (cat given away, euthanized or permanently separated).
  • Recent and mild (low-intensity, low-frequency) cases may have better long-term outcomes.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • Urine marking/spraying
  • House soiling
  • Excessive grooming
  • Fearful/anxiety-related behavior
  • Human-directed or interspecies aggression

Age-Related Factors

Predatory/Play-related aggression more common in young active and playful cats housed indoors with more sedentary or aged individuals.

Zoonotic Potential

Humans intervening while cats are fighting may be injured and contract infections through cat bites and/or scratches.

Pregnancy/Fertility/Breeding

Most behavioral medications are contraindicated in breeding animals.

Synonym

Feline intraspecies aggression

Abbreviations

  • FeLV = feline leukemia virus
  • FIC/FLUTD = feline idiopathic cystitis/feline lower urinary tract disease
  • FIV = feline immunodeficiency virus
  • MAOI = monoamine oxidase inhibitor
  • SSRI = selective serotonin reuptake inhibitor
  • T4 = thyroxine
  • TCA = tricyclic antidepressant

Authors E'Lise Christensen Bell and Kenneth M. Martin

Consulting Editor Gary M. Landsberg

Suggested Reading

Heath S. Feline aggression. In: Horwitz DF, Mills D, eds. BSAVA Manual of Canine and Feline Behavioural Medicine, 2nd ed. Gloucestershire, UK: BSAVA, 2009, pp. 223–235.

Landsberg G, Hunthausen W, Ackerman L. Feline aggression. In: Behavior Problems of the Dog and Cat, 3rd ed. Philadelphia: Elsevier Saunders, 2013, pp. 327–343.