Nearly one third of dog owning households in North America are multiple dog homes and nothing is more disturbing than when there is aggressive incidents between the dogs.  It can be dangerous for the dogs and for the human who intervenes to break up the fight, not to mention disturbing for the happiness of the humans living in the home.  Researchers at the Animal Behavior Clinic at Tufts University Cummings School of Veterinary Medicine in Grafton, Massachusetts recruited 38 pairs of dogs to specifically assess the characteristics of the dogs involved and what can be done to stop the fighting between dogs living in the same household.  The researchers conducted in-depth interviews and administered questionnaires to determine the characteristics of the dogs involved in aggressive situations then later prescribe a treatment for the problem.
Surprisingly enough, female dogs are more often to be involved in such fights than males.  While 32% of the fighting involved two males, 68% were female participants and, in addition, the injuries were more severe, the fights were longer and more furious.
When looking at the overall characteristics of the dogs involved, 70% of the instigators of the aggression are dogs recently brought into the household and in 74% of the cases, it is the younger dogs that starts the fight.  These conflicts can be quite intense with 50% requiring veterinary care and 10% of the owners needed medical attention for trying to intervene.  Of these intervening owners, 54% felt the fight would not stop unless they separated the dogs and 8% of the owners successfully separated the dogs by using learned obedience commands.
A trigger for 46% of the research pairs was the actions of the owner, such as paying more attention to one dog than the other while 31% involved simple excitement such as the owner’s arrival; 46% of the pairs involved conflict over food while toys or found items are triggers in 26%.  The rate of conflict was 39% when one of the dogs in the pair was adopted at the age of 12 weeks or older; 33% of the cases of conflict involved dogs adopted from a shelter and 16% involved dogs from pet shops.
Dogs involved in aggressive situations with the dogs they live with have a tendency to show aggression to other dogs by 40%, toward humans in the household by 27%, 27% toward human strangers and, sadly, 20% have shown aggression toward their owner.  In 50% of the pairs of dogs involved in conflicts, at least one member suffered noticeable separation anxiety while 30% had phobias, fearfulness, and other forms of anxiety.
This aggression between housemates is treatable using behavioral techniques instituted at home.  One is the “nothing-in-life-is-free” which requires the dogs to respond to a learned command such as “sit”, “down”, “come”, etc. before they get what they want like food, treats, attention, etc.  The second involves “supporting” one of the dogs by giving him everything first.  It could be the larger, stronger, and healthier or it could be the “senior” dog which means the one who has been with the owner the longest as well as the oldest.  Both of these methods work but it takes an average of five weeks or more after the process has started to see results.  The “nothing-in-life-is-free” technique produced improvement in 89% of the pairs and the “senior support technique” produced improvement in 67% of the pairs.  Because the dogs must act in a controlled manner, which takes the excitement out of the situation and events occur in a predictable order, are the reasons these techniques work.
The sex of the dogs makes a difference in the likelihood of improvement with behavioral treatment.  Conflict was reduced 72% in the male-male pairs, for male-female pairs reduction was 75%, but the reduction was only 57% in the female-female pairs; not as large as in the other pairings but well worth the effort.