Research Report: Dog-Dog Aggression in the Household

Written by Sally Foote, DVM

Canine housemate aggression is a serious behavior problem in many dog households. Accurate reporting of the incidence of housemate aggression is challenging. Few owners report fights between housemates to the veterinarian. Presentation for bite wound care is often the first indication to the veterinary staff of housemate aggression. The medical prognosis for a level 3 bite is good, yet there is little information on the behavior prognosis for a situation where intra-household aggression has resulted in a level 3 bite.b

Often owners treat these wounds at home. Without intervention, the aggressive behavior often continues to escalate, resulting in more injurious bites. As a general practitioner with behavior expertise, I would warn that any aggression was serious and needed immediate intervention.

Until recently, there was little information about risk and prognostic factors for intra-housemate aggression. A retrospective survey of intra-housemate aggressive canine cases was published in the Journal of the American Veterinary Medical Association in February 2020.1

Drs. Feltes, Stull, Heron, and Haug reviewed 305 housemate pairs for various characteristics and behavior outcomes. Previous survey data indicated female-to-female pairs, and new additions to the household were common presentations for aggressive behavior.2 This survey looked at behavior success outcomes and case presentation criteria to determine what factors were positively indicative of a successful outcome. The survey results are as follows:

  1. 70% of pairs had one female, with 61% being pairs of the same sex
  2. Resource guarding was a trigger in 72.8% of the cases
  3. The aggressor was acquired after the recipient in 59.3% of the cases
  4. On average, the aggressors were 16 months younger, and 3.3 lbs. heavier than recipients of the aggression
  5. Level 3 bites, and unprovoked attacks, resulted in poor outcomes for behavior success

Bites that break the skin were an important factor for predicting a high likelihood of future attacks and bites, despite human household members actively attempting to manage the aggressor’s triggers. The correlation between bites that break the skin, and low success in preventing future aggression, means that veterinarians should consider bite wounds as a signal for immediate behavior referral and intervention.

Even when a dog is presented for an unrelated medical issue, if they have healed nicks and wounds that indicate a history of fighting with another dog in the owner’s household, I would suggest that the veterinary staff must immediately refer to a certified veterinary or animal behaviorist, and record this in their medical record.

It is equally important that non-veterinary behavior consultants refer to the primary care veterinarian when they are presented with intra-housemate aggression, as the possibility of attacks despite behavior management is a health and welfare risk on the victim dog.

As a veterinarian, I seek evidence to support my evaluation, advice, and prescription of care for medical and behavior problems. Veterinary behavior science continues to grow with research and studies to build our knowledge. The results of this retrospective survey give specific criteria for emergency and general practice veterinary staff to refer for behavior consultation. Canine health and welfare can improve with this additional knowledge.

Shelter staff can use the information from the Feltes et al. study to continue improved housemate adoption criteria. Intra-housemate aggression is a common behavior problem cited by owners relinquishing their dogs to a shelter.3 Post-adoption support for behavior can improve new adoptee retention.4 Many dogs have been placed into foster homes because of the covid-19 shutdown — with more people working from home and available to provide foster homes, coupled with shelters working to reduce their population to keep their staff safe and continue to operate despite not being able to use volunteers. Shelters should take this as an opportunity to review the dogs’ behavior in these placements, and screen for any brewing housemate aggression problems so they can offer support and advice. Veterinary staff should also use the study data for better resource management advice for aggression prevention, as resource guarding was one of the strongest predictors of aggression, but also correlated to successful outcomes for managing the problem.

I am very encouraged by this study, and I look forward to more surveys in the future. Risk factors and prognostic data for behavior problems provide veterinarians the numbers they need to confidently advise for behavior referral. Animal behaviorists can use the same data to inform and advise for veterinary support to the behavior plan knowing the impact on victim health and welfare in housemate aggression cases. This is one way to continue to build the bridge between veterinary and non-veterinary behaviorists.


  1. Feltes, E., Stull, J. Herron, M. and Haug, L. Characteristics of intrahousehold interdog aggression and dog pair factors associated with poor outcome. American Veterinary Medical Association website, accessed 6/2020.
  2. Dodman, N. (2011) Interdog household aggression: 38 cases. Journal of the American Veterinary Medical Association 238:6, 731-40.
  3. Donaldson, J. (2000) Behavior problems and long-term housing. Maddie’s Fund website, accessed 6/2020.
  4. Gates, M., Zito, S., and Dale, T.A. (2018). Post-adoption problem behaviours in adolescent and adult dogs rehomed through a New Zealand shelter. Animals 8:6, 93.