ISSN 2398-2950      

Aggression: intercat



  • When considered as a descriptor of normal feline behavior, intercat aggression is most commonly seen between toms.
  • In most wild, feline social systems, few males mate with most of the females.
  • The form of intercat aggression that is pathological and with which most clients are concerned is more commonly based on conflicts within social hierarchies than it is with sex.
  • For aggression between cats which may be considered "normal", the skewed sex ratio in the breeding population is induced and maintained by vigilance and aggression on the part of the males.
  • There is an additional olfactory component of spraying and non-spraying marking that contribute to this type of aggression.
  • The aggressive behaviors are classic and involve flattened ears, howling, hissing, piloerection, threats using eyes, teeth, and claws and combat.



  • The etiology is poorly understood for this condition, as for most behavioral conditions.
  • At the phenotypic level the aggressor appears to be unable to take his or her behavioral cues from context - or to accept the information they convey - and instead must provoke the situation.
  • This is a classic anxiety response, since, by definition, anxiety-related conditions are defined, in part, from an inability to develop rule structures in the absence of control of contextual situations.
  • It's important to note that the cat(s) who are the victims of the aggression may be behaving perfectly normally, signaling perfectly normally, and going out of their way to avoid any aggressive interaction.
  • Key to the situation is that this makes no difference to the aggressor: he or she either ignores these cues or cannot understand and make use of them in a manner that would allow him or her to alter the aggressive behavior.

Predisposing factors


  • Intercat aggression becomes more common with over-crowding and decreased individual space (both linear and 3-D).
  • Cats who previously lived in harmony may become destabilized by the addition of another cat.
  • Researchers have noted that when cats can form triads, these can be destabilizing factors.
  • Some cats are truly abnormal and will not tolerate other cats and will bully any other cat regardless of the appropriateness of the other cat's behavior or its response to the aggression and bullying.
  • These abnormal cats may have a genetic predisposition, or may have had incomplete exposure to other cats while growing up.
  • There is insufficient data on all of these topics, so no firm conclusions can be drawn; however, cats whose parents are friendly and who were not socially deprived as youngsters are included in the pool of cats who are aggressors or bullies.


  • We know little about the pathogenesis of any behavioral problems, including this one.
  • That the condition occurs at social maturity and is likely based in anxiety is informative.
  • It is likely that neurochemical changes in the amygdala and frontal cortex during social maturity are associated with this fulminate aggression.
  • It's also possible that the hypothalamus, particularly the lateral hypothalamus, is stimulated because of its known association in laboratory experiments in active biting attack.
  • Recent data on other mammalian species suggest that glutamate is involved in most explosive aggressions, and that it may act as a cytotoxic excitatory amino acid functioning as a neurotransmitter in these fulminate situations.
  • Glutamate is metabolized by glutamate decarboxylase (GAD) to gamma amino butyric acid (GABA).
  • Some dysregulation of this pathway has been proposed in both impulsive aggressions and epileptogenic events.
  • In other species, glutamate is known to increase, and GAD to decrease, post-event, and there is some data to support a rise in glutamate preceding the event.
  • These associations are largely unexplored in cats and are wholly clinically unexplored.
  • The association with glutamate may explain why diazepam, which augments GABA helps to raise the threshold for such events in some cats.
  • In other cats, benzodiazepines act to dis-inhibit aggression that is already actively inhibited (inhibition of an inhibition), rendering the cat much more aggressive.
  • Given the metabolic pathway, this finding may suggest that different pathogenic mechanisms are involved for these 2 groups of cats, as defined by their response to diazepam.


  • Like almost all other behavioral conditions (except for forms of panic and phobias) the longer that the aggression has been ongoing the better honed the skills of the aggressor(s) and the responses of the victim(s).
  • The problems generally start as one of the cats is entering or is in the midst of social maturity.
  • Unfortunately, when cats are known to each other, the early forms of aggression are usually covert, as previously discussed.
  • The aggression only becomes overt when the relationship degenerates to the point that covert threats are not sufficient to get the response the aggressor desires.
  • If clients can learn to anticipate the risks associated with developmental stage and the addition of other cats they can be taught to look for the covert behaviors that precede frank aggression.
  • If the clients can intervene at this stage, they may alter the timecourse of the condition.


  • It has long been noted that triads in cats are unstable because coalitions may form if there had been any tension beforehand, or if the addition of a new animal provokes concern in one half of the original dyad.
  • Unfortunately, the more cats that are added, the more common and complex the combinations of stable v. unstable coalitions.
  • Left to their own, domestic cats live in relatively stable groupings that are structured along matrilineal lines.
  • Immigration of females is likely rare, although males both emigrate and immigrate at social maturity, or earlier if resources are limiting.
  • Accordingly, the cats that stay within the group grow up knowing each other, and those who enter become known by the others within their existing framework of relationships.
  • Social learning then becomes a gradual and ongoing process that also takes into account ontogeny and maturity.
  • This is not the case in most feline households.  These cat are not generally related, did not grow up together, did not share histories, and did not have the benefit on undergoing ontogeny and maturity along with others in the household.
  • It's important that clients understand the importance this such differences may play in how their cat household may interact.
  • Given how social and complex cats are it's actually impressive that so many mixed ancestry households do so well.


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Overall K L (2004) Paradigms for pharmacologic use as a treatment component in feline behavioral medicineJ Feline Med Surg (1), 29-42 PubMed.
  • Ogata N & Takeuchi Y (2001) Clinical trial of feline pheromone analogue for feline urine marking. J Vet Med Sci 63 (2), 157-161 PubMed.
  • Pryor P A, Hart B L, Cliff K D et al (2001) Effects of a selective serotonin re-uptake inhibitor on urine spraying behavior in cats. JAVMA 219 (11), 1557-1561 PubMed.
  • Hunthausen W (2000) Evaluating a feline facial pheromone analogue to control urine spraying. Vet Med 95 (2), 151-154 VetMedResource.
  • Frank D, Erb H N & Houpt K A (1999) Urine spraying in cats: presence of concurrent disease and effects of a pheromone treatment. Appl Anim Behav Sci 61 (3), 263-272 VetMedResource.
  • Overall K L (1999) Intercat aggression: Why can't they all just get along? Vet Med 94, 688-693.
  • Overall K L (1998) Tracing the roots of feline elimination disorders to aggression. Vet Med 93 (4), 363-366 VetMedResource.
  • Seksel K & Lindeman M J (1998) Use of clomipramine in the treatment of anxiety-related and obsessive-compulsive disorders in catsAust Vet J 76 (5), 317-321 PubMed.
  • Overall K L (1997) Animal Behavior Case of the Month: Intercat aggression associated with spraying and urine marking. J Am Vet Med Assoc 211, 1376-1378.
  • Bernstein P & Strack M (1996) A game of cat and house: Spatial patterns and behavior of 14 domestic cats (Felis catus) in the home. Anthrozoös 9 (1), 25-39 VetMedResource.
  • Center S A, Elston T H, Rowland P H et al (1996) Fulminant hepatic failure associated with oral administration of diazepam in 12 catsJAVMA 209 (3), 618-625 PubMed.
  • Hughes D, Moreau R E, Overall K L et al (1996) Acute hepatic necrosis and liver failure associated with benzodiazepine therapy in cats, 1986-1995. J Vet Emerg Crit Care (1), 13-20 VetMedResource.
  • Adamec R E (1975) The neural basis of prolonged suppression of predatory attack.  I.  Naturally occurring physiological differences in the limbic system of killer and non-killer catsAggr Behav (4), 315-330 Wiley Online Library.

Other sources of information

  • Overall K L (2004) Manual of clinical behavioral medicine for small animals. Elsevier, St. Louis.
  • Seksel K (2001) Training your cat, Hyland House, Australia.
  • Beaver BV (2000) Feline behavior: a guide for veterinarians, 2nd edition, WB Saunders, Philadelphia, 2000.
  • Horwitz D, Heath S, Mills D (2000) BSAVA Manual of canine and feline behavioural medicine.  BSAVA, Gloucester UK.
  • Overall K L (1997) Clinical behavioral medicine for small animals.  Mosby, St. Louis.

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field