Canine aggression toward unfamiliar people and dogs (Proceedings)


Dog aggression is a serious public health issue in the U.S.

Dog aggression is a serious public health issue in the U.S. Aggression to unfamiliar people and dogs is inarguably the most common aggression issue addressed by veterinary behaviorists in dogs. Fear aggression is the most common diagnosis in dogs aggressive to unfamiliar stimuli even when elements of territoriality are present. Offensive posturing by the dog does not rule out anxiety or fear as an underlying cause.

The development of aggressive behavior frequently is complicated and multifactorial. Problems associated with aggression in dogs fall into two broad categories: 1) normal dogs expressing normal, but unacceptable behavior, or 2) abnormal dogs reacting out of context to the environment. Perinatal factors (intrauterine environment, maternal and sibling interactions), experience (socialization and learning), and biological correlates (genetics, hormones, and neurophysiological factors) all impact the expression of the behavior.

Socialization deficits are inarguably the most prominent factor in the development of aggression in physiologically normal dogs. Roll and Unshelm noted that 44% of a population of dog-aggressive dogs had few or no interactions with conspecifics from 5 weeks to 5 months of age. Mere exposure to other people and dogs is not sufficient to guarantee adequate social skills.

Selecting the most appropriate treatment course will depend on the animal's behavioral phenotype and the owner's resources and capabilities. Clinicians should carefully explain each step of the treatment process. Demonstration of techniques should also be performed where appropriate and feasible. Owners must understand that altering the dog's behavior will take time, and improvement may not occur in a linear fashion. For some owners, the number of environmental changes and interventions can be overwhelming. Breaking the interventions down into progressions will help owners successfully accomplish goals and see more rapid response.


Owners must find ways to safely exercise their dogs. This means walking the dog at times and in places where they are unlikely to encounter other people or dogs, even if the owner must drive the dog to an acceptable area. Mental stimulation via environmental enrichment helps occupy dogs that have limited physical exercise routines and that are left alone for long periods. Rotating toys, feeding from food-dispensing devices, and engaging the dog in activities requiring problem solving (e.g. training and discrimination tasks) all should be part of the dog's normal routine. Training even simple tricks is excellent mental stimulation and helps strengthen the dog-owner bond as well as increasing the dog's skill set.

Most aggressive outbursts occur repeatedly in a handful of contexts such that these environments alone now predict the appearance of unfamiliar dogs and people. Temporarily removing the dog from these contexts and from exposure to trigger stimuli will facilitate the conditioning of more desirable behavioral responses. Avoidance also reduces the risk of injury to other people and dogs. The dog should not be exposed to any such stimuli until later in the rehabilitation process and only during controlled training sessions.

Inside the house, the dog should be prevented from patrolling windows and doors for passing people or dogs by blocking windows (e.g. closing blinds) or gating the dog away from the front of house, especially in the owner's absence. If necessary, the dog can be crated or closed into a room with no or few windows and protected from outside noises. When visitors arrive, the dog should be confined before the visitor actually enters the house

Helping the owner gain some sense of control over the dog is a valuable step early in a behavior program. Muzzle-loop head collars such as the Gentle Leader (Premier Pet Products, Inc., Richmond, VA) are especially advantageous for large and/or aggressive dogs. These collars provide excellent control over the dog's head. Dogs with a previous bite history, with severe or escalating aggression, and/or with owners that have difficulty controlling them should be trained to wear a muzzle.

Dogs that are visually reactive may benefit from a product such as the Calming Cap (Premier Pet Products, Inc., Richmond, VA), elastic, semi-transparent cloth "hood" that covers the dog's eyes

Foundation exercises

Few dogs with aggressive behavior are sufficiently proficient at even basic obedience behaviors. While obedience itself will not resolve an aggression problem, these cues are important as a way for an owner to request alternative responses from the dog. The goal of training is twofold: 1) obtain reliable response to the cues and 2) condition the dog to become calm and relaxed when performing the behaviors. The latter is crucial and is done by rewarding the dog only for relaxed responses once the dog has a basic understand of the behavior itself. At minimum the dog should be able to respond to cues for sit, down, stay, and come. The dog should be able to walk calmly on leash by the owner's side and also respond to its name by orienting to the owner. Targeting exercises (e.g. dog touching its nose to a target stick or the owner's hand) are also invaluable. These are easy behaviors to teach and easy for the dog to learn resulting in a typically highly reliable behavior. Among other things, targeting can be used to reorient a distracted dog and to lead or lure the dog away from a problematic situation. All behaviors should be trained using positive reinforcement.

The owner should begin to establish consistent behavioral criteria for any interaction with the dog (i.e. petting, feeding, starting a training session, putting on the dog's collar, opening doorways, etc). These include: respond to any requested cue behavior (e.g. sit) within an established time frame; remain calm during the entire interaction; remain focused on the owner during the interaction; and remain outside a previously designated "personal space" around the owner.

Safety cues and relaxation tasks

Animals readily make associations between contextual (environmental) stimuli and emotional experiences that occur when those stimuli are present. Safety signals are environmental stimuli that become paired with relaxed physiologic states in safe environments. Safety signals can be tactile, olfactory, visual or auditory. Safety cues should be portable and easy to reproduce, but also fairly unique to the environment in which they will eventually be used (e.g. out on walks, at the vet clinic, when visitors come over). This prevents the dog from habituating to their presence in the environment. The dog should only be exposed to the safety signal during conditioning sessions to ensure that the pairing of cue and relaxation remains as consistent as possible.

Relaxation must be taught to the dog in a methodical manner in an environment initially free of distraction. Structured down-stay (or sit-stay) exercises should be practiced as a baseline relaxation task. The dog is trained to maintain a short, relaxed down-stay and then gradually exposed to increasing levels of generic environmental distractions and human activities. To further increase the dog's baseline relaxation, behaviors that a dog exhibits voluntarily when normally relaxed can be reinforced and placed on cue. Because the dog already is inclined to perform these behaviors, they are relatively easy to put under stimulus control.

All exercises are first trained within the owner's home in a quiet environment. Once the dog is proficient, the tasks are repeated in other areas both on and off the owner's property. The dog should never be asked to perform in an environment that it is not yet ready to handle. If the dog is asked to hold a relaxation position when it is in a stressful environment, this will erode the value of the behavior as a safety cue.

Stimulus-specific behavior modification exercises

Stimulus-specific exercises center on desensitization-counterconditioning (DCC) drills. Typical methodology has both classical and operant conditioning components although variations may focus heavily on one element over the other. In traditional DCC, the animal is exposed to a low level stimulus. The presence of the stimulus is paired with something the dog finds rewarding such as food or play. The previously described down-stay relaxation task serves as the foundation for stimulus-specific DCC. The trigger stimulus becomes a new distraction added to the protocol. The dog is asked to sit or down-stay, preferably in the presence of a previously established safety signal, and then the dog is exposed to a low level stimulus (e.g. a dog or person) at a distance such that the dog briefly alerts but then returns focus to the owner. If the dog reacts to the stimulus, the stimulus is too close or too intense. The dog is then rewarded for remaining calm in the cued position.

For each stimulus category (e.g. dogs or people), the owner should develop a hierarchical list with the stimulus composition least likely to arousal the dog at the top and the stimulus composition most likely to trigger arousal at the bottom. The more intermediary stimuli listed the better. The owner should also determine the thresholds at which the dog 1) alerts/orients to the stimulus, 2) barks/growls, and 3) lunges or tries to bite. This list becomes the dog's general training syllabus.

Desensitization/counterconditioning sessions are divided into four base criteria: distance (between the dog and the trigger stimulus), duration (that the dog is exposed to the stimulus during any one trial), intensity (of the behavior or physical characteristics of the stimulus), and number (of stimuli present at one time during the trial). During any one trial, only one criterion should be manipulated.

Highly aroused dogs will benefit from beginning DCC with audiotapes of sounds associated with the trigger stimulus (e.g. dog tags, barking, footsteps on the sidewalk, human voices). This allows the owner to begin the process in the safety of the dog's home. For dogs with territorial aggression, sessions should include sounds of doorbells and knocking. The dog should also be trained to sit or lie calmly away from the door when the door is opened and someone enters. This is first accomplished with family members, then with familiar visitors, finally progressing to unfamiliar visitors.

Pheromone and aromatherapy

The canine olfactory system is well developed and represents a significant portion of the dog's brain mass. The olfactory system is highly connected to the limbic system. Dogs also have a function vomeronasal organ which transmits information to the accessory olfactory bulb and then on to the amygdala. Dog Appeasing Pheromone (DAP, Veterinary Products Laboratory, Phoenix, AZ) is a synthetic analog of the pheromone secreted by lactating bitches. Lavender scent can reduce excitability also increases relaxation.

Pharmacological intervention

Currently there are no medications labeled for treating aggression disorders in dogs. There are few controlled clinical studies evaluating drug therapy in aggressive dogs. Pharmacological intervention can facilitate or expedite behavior therapy in some cases. Benefit may be most likely if: 1) the aggression is related to high anxiety states or fearful behavior, 2) the animal appears to have a concurrent impulse control disorder, or 3) the dog is truly "reactive" where the behavioral profile supports the possibility of amygdalar hyper-reactivity. Serotonin reuptake inhibitors, which manipulate serotonin concentration in the synaptic cleft, currently remain the primary class prescribed for these problems. Clomipramine, buspirone and anticonvulsants such as carbamazepine have also been used.

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