Characteristics of intrahousehold interdog aggression and dog and pair factors associated with a poor outcome.

Objective: To describe characteristics of intrahousehold interdog aggression (IDA) and dog and pair factors associated with a poor outcome (permanent separation, rehoming, or euthanasia of dogs).
Animals: 305 pairs of dogs (610 dogs) with IDA.
Procedures: The record database of a referral veterinary behavioral clinic was searched to identify pairs of dogs that were evaluated for IDA (IDA pairs) between September 2007 and September 2016. A standardized form was used to extract data for each IDA pair, including signalment and acquisition order of both dogs, history of IDA, behavioral interventions implemented, and outcome. Descriptive data were generated. Univariable logistic regression was used to identify factors associated with a poor outcome.
Results: Most IDA pairs included at least 1 female dog (214/305 [70%]) and dogs of the same sex (188/305 [61.6%]). Resource guarding was the most common fight trigger (222/305 [72.8%]). Possessive aggression (guarding of physical resources) was the most common comorbidity for individual dogs (216/610 [35.4%]). The aggressor was acquired after the recipient in 181 of 305 (59.3%) pairs. Aggressors were a mean of 16 months younger and 1.5 kg (3.3 lb) heavier than recipients. Factors associated with a poor outcome included pairs of the same sex, history of bites that broke the skin, and aggression on sight of the recipient.
Conclusions and Clinical Relevance: Results suggested that behavior intervention should be provided quickly for IDA pairs with a history of bites that break the skin or uninhibited attacks on sight owing to the high risk for a poor outcome. Owners should be advised to avoid same-sex pairs during preadoption counseling.