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Aggression Between Dogs

Debra F. Horwitz DVM, Diplomate ACVB
Veterinary Behavior Consultations
St. Louis, Missouri

Canine social aggression usually occurs in two types of circumstances. The first is aggression toward unfamiliar dogs that are encountered on walks or other social settings. The second is aggression between familiar dogs that live in the same home. Aggression between dogs can result in injury to dogs and to people trying to separate them. The aggressive behavior can consist of lunging, growling, snarling, barking, snapping and biting.

Aggression between familiar dogs that live together (sibling rivalry)

Fights between dogs in the household are usually about dominance-or social status aggression. These fights commonly occur when dogs reach social maturity, about 18-24 months of age, but the range is 12-36 months. Fights will be about those resources that are considered most important to dogs. These include food, resting-places, territory, favored possessions, and favored people. Fights then can occur over treats, owner attention, greeting the owner upon return, sleeping positions near the owner, entering or exiting the home, high arousal situations such as fence running, or movement through tight spaces. These fights occur most often between dogs of the same sex and seem to be most severe between female dogs1. Conflicts can occur between dogs where the dominance status is ambiguous, in other words they appear to be close in rank, or fights can occur between dogs where one is clearly dominant. In these situations it may be difficult to determine which dog is the dominant one, and often dominance can be context specific with one dog dominant in one situation, and the other dog dominant in another. Hierarchies may not always been strictly linear. Regardless, the fighting can be severe and injurious. Under no circumstances should the dogs be encouraged to "fight it out", this can result in severe injury and/or death. When dogs in a household fight, the owners can be injured in redirected aggressive attacks.

One scenario that can result in interdog aggression is when a younger, larger, more agile dog challenges an older, previously dominant dog. This is often clearly an attempt to alter the existing hierarchy. Sometimes the older dog will acquiesce and things are fine, other times, the owners do not want the change and intervene. Still in other situations, the older dog will not relinquish the dominant role. Interdog aggression can occur between dogs that were raised together, and are now reaching social maturity with a resulting shift in the social relationship. Lastly, interdog aggression can occur when the dominant dog leaves the household for some reason and the existing dogs try to restructure the hierarchy or when a new dog enters the home.

History taking should focus on what circumstances elicit the aggression, what the owners were doing, and how they responded to the aggressive behavior of either dog. The progression of the aggression should be explored; this may help indicate causation and/or maintenance factors for the behavior. The use of punishment must be explored and addressed. The length of time that the aggression has been present and the injuries of the dogs to date are important in determining prognosis. The ages of the animals involved may also determine treatment and prognosis. Owner ability to identify and predict aggressive episodes as well as ability to understand and carry out treatment recommendations will effect results.

Aggression between household dogs can be difficult to treat. Sometimes the problem presents such that one dog is clearly dominant to the other, and the subordinate dog does not challenge if the owners do not interfere. If left to their own devices, the dogs will often use posturing and threats to end encounters without injury. The first step is explaining canine dominance hierarchies to pet owners. Often they do not understand what hierarchies do, and how they are maintained. The concept of dominant and subordinate relationships between animals was developed from observation of animals (wolves, baboons, chickens) living in social groups2. Social hierarchies arranged around dominant and subordinate relationships decrease the conflict associated with the allocation of critical resources, i.e. food, shelter, mates and territory2. When living in social groups, canids will establish dominance hierarchies that may dictate access to certain resources such as food, resting-places, favored possessions, territory and mates but may or may not involve aggression3. However, a case could be made that dominance behavior may occur without aggression and instead be about control of the outcome. In domestic canid groupings, overt aggression is rare and deference common4. Another common owner error is the desire to make life "fair". This often results in owners allowing subordinate dogs access to resources, such as owner attention, treats etc., entry into territory, that they would not normally have. The dominant dog may become aggressive toward the subordinate dog to "enforce the rules". This usually results in punishment for the dominant dog. The subordinate dog then learns it can engage in prohibited behavior while the owner is present. At times no fighting occurs when the owners are gone, in fact the owners often leave the dogs together because they never come home to an injured dog. While the dogs are alone, they are aware of the hierarchy and often the subordinate dog does nothing to challenge the dominant animal. In this situation, if there has not been injury to either dog, and the aggression has been limited to threats, treatment has a better prognosis.

Usually treatment is centered on supporting the dominant dog. In some cases this is the younger, bigger, more physically capable dog. Often, this is also the aggressor, and this goes counter intuitive to what most owners want to do. At other times a technique called "elder support" is used which entails supporting the dog that is older and has been in the home the longest5. Whichever technique is chosen, it means that the dominant dog has access to everything first-to go outside, to come in, food, owner attention, entry into rooms where the dominant dog and owner are. If the owner is petting the dominant dog and the subordinate dog approaches, the subordinate is sent away and made to wait. Attempts are made to avoid circumstances that elicit aggression. The dogs are separated when unsupervised. If the more dominant dog approaches the subordinate dog and the subordinate dog assumes subordinate postures, the owners are not to intervene. Some owners are able to do this, and the dogs respond and the aggression ceases.

Another technique often used in conjunction with the above is to make the owner dominant to both dogs when the owner is present. Both dogs should be separated when not supervised to avoid injury. It is also helpful for owners to learn how to recognize canine body language and low-level threats such as eye contact, snarls or low growls. Owners are also instructed to keep records of threats, attacks, or tension producing situations. To facilitate treatment, both dogs should be fitted with headcollars (Gentle Leader/Promise-Premier Pet Products) for owner control or muzzles. The owner needs to feel confident that control of the dogs is possible, and no further injury is going to occur. All privileges are withdrawn from both dogs. The circumstances that elicit aggression are avoided. Owners are told to keep greetings low key, avoid treats and rawhides unless separated or on leash, avoid or control movement through tight spaces. The owner is instructed to train each dog separately to commands for sit, stay and down to increase control. Then, the dogs are put into subordinate positions such as sit/stay or down/stay and only allowed to interact with the owner at owner commands. The owner controls all interactions and access to food, resting places, territory, owner attention and treats. The owner is to not play "favorites" but treat the dogs equally at all times. The dogs are leashed when in the house together, and the leashes fastened to furniture.

Another helpful treatment modality is to have the dogs interact in a situation that is neutral where they are both happy. This could be a walk. It is usually best to have two individuals to walk the dogs and not to allow them to forge in front of one another. Another helpful training situation is to feed the dogs at a distance, far enough apart that they do not show aggression. Slowly the dishes are moved closer together as long as the dogs do not react. The food serves as a passive reward in this situation. If the dogs react, the food bowls are moved further apart6. Headcollars aid in good owner control on walks as well as in the home. When the owner is not home or supervising the dogs, the dogs are separated or crated. It is also important to talk to owners about how to break up fights should they occur. Owners usually try to reach for the collar of the fighting dogs, or if one is small, pick it up. This can result in severe owner injury if the fighting is very intense. Anxiolytic medication may be appropriate in some cases.

When owners intervene in fights, redirected aggression is possible. Redirected aggression is aggression (growl, snarl or bite) redirected to a person, animal or object other than that which evoked the aggression7. If during the course of a dogfight, one owner picks up an animal, the other animal may continue to attack and direct that attack at them. Dogs can also redirect aggression under other circumstances as well including dominance aggression, possessive aggression, territorial aggression and during attention seeking behaviors8.

Prognosis can be extremely variable. When blending households, some family members may refuse to make one dog subordinate even if it is willing and clearly the other dog is dominant. At times the terrier breeds can persist in aggressive behavior despite owner control and intervention, and in those cases alternate living arrangements may need to be made.


1.  Sherman, CK., Reisner, IR., Taliaferro, LA. & Houpt, KA.: Characteristics, Treatment and Outcome of 99 Cases of Aggression Between Dogs. Applied Animal Behavior Science 47 (1996) 91-108.

2.  Alcock, J, Animal Behavior: An evolutionary approach. Edition 2. Sunderland, Mass, Sinauer Associates Inc. 1979.

3.  Voith, VL, Borchelt, PL, Diagnosis and treatment of Dominance Aggression in dogs, In: Veterinary Clinics of North America: Small Animal Practice, Vol. 12:4, 1982, pp. 655-663.

4.  Bradshaw, JWS, Nott, HMR. Social and Communication behaviour of companion dogs. In: The Domestic Dog, J. Serpell Ed. Cambridge University Press. Cambridge, 1995, pp. 116-130.

5.  Dodman, NH, Arrington, D Animal Behavior Case of the Month. JAVMA 217: 1468-1472, 2000

6.  Overall, KL.: Animal Behavior Case of the Month. JAVMA 207: 305-307, 1995.

7.  Borchelt, PL. & Voith, VL.: Classification of Animal Behavior Problems. Veterinary Clinics of North America: Small Animal Practice.12:4. Philadelphia, W. B. Saunder Co. 1982. pp. 571-585.

8.  Overall, KL.: Animal Behavior Case of the Month. JAVMA 207: 305-307,1995

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