Sister Dogs–Household Inter-Dog Aggression

Authored by Lynne M. Seibert, DVM, MS, PhD, DACVB, Veterinary Behavior Consultants LLC

Excerpt from the Georgia Veterinarian Magazine, Summer 2020 Edition

It has been reported for household inter-dog aggression that the instigator of aggression is often either the younger dog, or the newer addition to the household.1 The same study found that fights most often occurred between dogs of the same sex. A more recent study also noted a high frequency of household inter-dog aggression cases [79%] involved same-sex pairs.2

CLASSIFICATION. Classification of aggression can vary. Aggression is often classified according to a combination of eliciting stimuli, context, function, motivation, and behavioral components. At the most simplistic level, aggression can be classified as either affective or non-affective. Non-affective aggression includes predation. The behavior is of hypothalamic origin, mediated by acetylcholinergic activity, and is triggered by moving prey. Affective aggression is associated by marked mood change, autonomic activation, and frontal cortex or amygdala involvement.

Fight-eliciting triggers between dogs who live in the same household, have been reported to include owner attention or proximity, food, found items, physical resources, confined spaces, or excitement. Other causes of household inter- dog aggression include fear, pain, irritability, predatory behavior, owner protective behavior, or hierarchy instability.

CANINE SOCIAL GROUPS. Social groups are characterized by a complex system of communication. Stable social group membership requires mutual recognition of members and a system for allocation of group resources. Agonistic interactions include the behavioral repertoire of both aggressive/assertive and submissive actions within the context of a social interaction. Submissive postures function to terminate aggression and allow avoidance of combat. Assertive and submissive displays are stereotyped, such that components appear in a characteristic order.

A dominance relationship exists when one individual performs submissive responses at the onset of an agonistic encounter with another member of the group, based on the outcomes of prior interactions with that individual. Dominance relationships function to reduce the occurrence of competitive conflicts between members of an established social group, allowing peaceful allocation of limited resources.

Dominance relationships appear to require periodic reinforcement, even in the absence of incentive, to prevent extinction. Agonistic encounters are more frequently observed when status relationships are unclear. Once relationships are established, social interactions are consistent, resulting in fewer, or less intense, competitive conflicts.

Domestic dogs posture assertiveness by leaning forward, holding their heads up, maintaining direct eye contact, perking their ears forward, and straightening and placing weight on the forelimbs. Assertive individuals may also stand over other dogs, place their muzzles over the head or body of another dog, or mount another dog. Tail wagging is a non-specific sign indicating arousal.

Domestic dogs signal submissiveness or deference by lowering the body, flexing the forelimbs, turning the head to the side, averting or avoiding eye contact, lowering the ears or turning them to the side, licking the face of another dog, or rolling over. Young puppies are almost always submissive to more mature members of their social group. Dogs of any age are almost always submissive to humans. Humans naturally, and constantly, assert themselves over their dogs by petting dogs on the head, maintaining eye contact, petting on the back or belly, and controlling the resources. No additional effort is needed to ‘establish dominance’ over a dog. Aggression between dogs might involve status (dominance), but dog aggression directed toward humans rarely involves status.

HISTORY. Collecting a thorough history is crucial for diagnosis and treatment. History taking should include information about the postural signals of each dog, and the context, location, instigator, and outcome for any aggressive episodes. Specific information about postural signaling between the dogs, outside the context of play, is helpful.

TREATMENT CONSIDERATIONS. Prognosis depends on the size of the dogs, severity of aggression, and seriousness of injuries to both dogs and humans. The first phase in the treatment of any aggression problem is learning to avoid the situations that elicit an aggressive response. This minimizes danger and prevents reinforcement of the behaviors. The safety of the dogs, as well as of the humans, should be considered. The dogs should be separated when they cannot be supervised to prevent injury. Basket muzzle training can be initiated for use during gradual introductions and desensitization sessions. Both dogs should be taught to sit and relax on cue, using positive reinforcement training. Postures consistent with a relaxed dog include, a closed mouth (no panting), soft lips (no tension), and forward ears.

MEDICATIONS. No drugs are approved for the treatment of aggression in dogs. Any psychotropic medication can have unexpected results, including increased arousal and disinhibition of aggression. Clients need to be informed that there are no “quick fixes” for complex behavior problems and that aggression problems are controlled, not cured.

POSSESSIVE AGGRESSION (RESOURCE GUARDING). Possessive aggression, also called resource guarding, occurs when the dog is in possession of a valued object, and another dog approaches, or attempts to retrieve the object. When the valued object is food or the food bowl, it is often referred to as food-related aggression. Only dogs displaying possessive aggression with no other signs of dominance-related aggressive behavior are included in this category.

Desirable objects may include food, a favorite toy, treat, bone, contraband, crate, bed, or family member. The aggression is object-specific, rather than location-specific. Postures of the aggressor can vary from submissive to assertive. Possessive aggression is not synonymous with dominance-related aggression. Submissive individuals may be highly motivated to guard their resources.

Resource guarding is managed by identifying situations in which aggression may occur, and avoiding or preventing them. The dogs should be separated during feeding, and any treats or toys should be removed when the dogs are together. The instigator can be desensitized to the other dog approaching him when he is in possession of resources. An object relinquishment cue can also be taught.

DOMINANCE-RELATED PROBLEMS. Dominance-related inter-dog aggression is associated with agonistic signaling between the dogs that is excessive or abnormal in its resolution. Competitive conflicts occur in the absence of resources. Steps to stabilize the hierarchy may include reinforcing one dog as the higher-ranking individual in the household, providing attention, food, and other resources first. Attempts by pet parents to impose a system of equality may increase inter-dog aggression.

Appropriate status signaling behavior between the dogs is reinforced, while inappropriate signaling is interrupted. Pet parents are instructed to interrupt interactions if dominance displays do not cease when the subordinate dog defers. The instigator may benefit from medication with a serotonin reuptake inhibitor.

FEAR AGGRESSION. Fear-related aggression, sometimes referred to as defensive aggression, is diagnosed when the aggressive dog is showing postures consistent with fear directed at the other dog, presumably when he is unable to avoid the interaction. Postures of defensiveness include holding the ears back or to the side, lowering the tail, lowering the head or crouching, caudal retraction of the lip commissure, and shifting the weight away from the other dog. The fearful dog can be desensitized to approaches from the other dog. If the fear response is severe, anti-anxiety medication may be indicated.

EXCITEMENT-INDUCED AGGRESSION. Excitement-induced aggression occurs only in the context of the instigator becoming highly aroused, resulting in aggression directed at a housemate dog. Common scenarios may include barking at a neighborhood dog, barking at the doorbell, or becoming reactive on a leash walk, and then predictably attacking the housemate. Successful treatment of arousal-related aggression requires treating the primary source of arousal. The instigator should be desensitized to the stimuli that cause arousal.


  1. Sherman CK, Reisner IR, Taliaferro LA, et al. Characteristics, treatment, and outcome of 99 cases of aggression between dogs. Appl Anim Behav Sci 1996;47:91–108.
  2. Wrubel,K, Moon-Fanelli, A, Maranda, L, Dodman, N. Interdog household aggression:38 cases (2006– 2007). JAVMA, Vol 238, No. 6, March 15, 2011.
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