Intrahousehold Interdog Aggression

Interdog aggression in a home can be disturbing and frustrating to pet owners, disruptive to everyday life, and potentially dangerous to both the owner and the dogs. The more that can be understood about this problem, the better advice a clinician can give the owner.

This review presented the results of a large, well-designed study that evaluated 305 pairs of dogs (217 included in outcome analysis) presented to a behavior referral practice for aggression toward each other. Cases reviewed had ≥6 months of follow-up or ≥1 of the dogs euthanized or permanently removed from the home. Multiple factors were assessed to determine correlations between interdog aggression and long-term outcome. Many of the results also support previous studies.^1,2

Intrahousehold interdog aggression is typically associated with dog pairs in which resource guarding is a trigger, a fighting pair of dogs that includes ≥1 female dog,¹ dogs of the same sex,¹ situations in which the aggressor dog was acquired after the recipient dog and is younger,² and aggressor dogs that are purebred but not breed-specific.^1,2 Several of these correlations were seen in ≥50% of the cases.

For the 217 pairs that were followed long-term, 55 pairs (25.3%) had poor outcomes, which included 23 pairs that required complete separation from one another, 24 involving ≥1 dog being euthanized, and 8 involving ≥1 dog being rehomed.² Of the remaining 162 pairs with a better outcome, 100 (61.7%) did not have to be separated following behavioral intervention, 32 (19.8%) were separated during triggers, 21 (13%) were kept separate when unsupervised and during triggers, and 9 (5.6%) were kept muzzled when together and supervised.²

Key pearls to put into practice:

Risk factors significantly associated with a poor outcome (eg, euthanasia, permanent separation of the dogs) in dogs with interdog aggression include^1,2:

• Dogs of the same sex, particularly female–female
• A bite serious enough to puncture the skin of the recipient
• The aggressor is ≥2 years younger than the recipient.
• The aggressor was introduced into the household after the recipient.
• An aggressor that is heavier than the recipient
• The aggression is triggered by the sight of the recipient, even without other triggers.
• The owner uses positive-punishment/negative-reinforcement training techniques.

Management is a particularly important part of treatment and should be strongly encouraged when clinicians become aware of the problem. Triggers should be removed if possible. The dogs should be kept separate from each other—particularly if eye contact alone triggers the aggression, when triggers are present, and when unsupervised. Muzzles are recommended, and appropriate muzzle training is emphasized. A variety of psychopharmacologic medications may be helpful. In this study, such medications were prescribed for 82.4% of aggressors and 32.7% of recipient dogs.

Ultimately, when historical information points to risk factors associated with poor outcomes (as described above), strong and immediate intervention is called for by the clinician, often including referral to a board-certified veterinary behaviorist.