Dog bite expert & animal behavior specialist

Richard H. Polsky, PhD, CDBC
Los Angeles, California

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Dr. Richard Polsky - The Dog Expert


Factors influencing aggressive behavior in dogs

This article was authored by Dr. Polsky, and published in 1983 in California Veterinarian. The content has been updated to be consistent with more recent findings in animal behavior as it pertains to aggression in dogs.Aggressive dog

This article is written by a behavioral specialis; that is, a Ph.D trained animal behaviorist who diagnoses and treats behavioral problems in companion dogs and cats. Like other workers in this ?eld, I have found that the primary reason why owners consult an individual with my expertise is because their pet is behaving too aggressively. This makes sense since the extent to which owners can make practical life style adiustments. or deal with the problem themselves, is probably seriously compromised when it comes to the aggressive dog. Hence, owners are often forced to seek help from an animal behavior specialist.

A recent reminder of how dangerous a dog might become appeared in the August 19, 1983, issue of the L.A. Times. The case involved a 60-pound bull mastiff who grabbed a 10-year-old girl by the neck while she stood on her porch. The dog pulled the girl down and began shaking her while she screamed “Don?t let him kill me.” The girl was clawed and bitten on the left side of her face before the owner pulled the dog off. The girl was then taken to hospital for surgery in an attempt to save a damaged left eye. Prior to the attack on the girl, this very same dog chased a small boy who was walking down the street, and then attempted to attack another person who escaped by running into her house.

The behavior of this particular bull mastiff was obviously extreme: Most dogs do not behave in this fashion. However, at the same time, we still must accept the fact that all too many of our canine friends continue to exhibit unusually high levels of aggression. The statistics speak for themselves: Annually, in the U.S. there are an estimated between one and five million dog bites! Even more shocking is the fact that, in the years 1974-1975. eleven people, including 2 infants, were killed by dogs, and in more recent years, the annual dog bite fatality rate has increased considerably.

One job of the applied animal behaviorist is to analyze factors responsible for the causation of aggression. Another job, once the proper diagnosis has been made, is to subject the dog to appropriate treatment procedures. lt goes without saying that if one doesn’t make the proper diagnosis, or it one doesn’t have a clear understanding of the causal factors involved, then subjecting a dog to the proper treatment procedures becomes problematic.

Recent text books and publications in animal behavior and veterinary journals have been of tremendous help in establishing guidelines to follow in dealing with aggressive behavioral problems displayed in the context of the home environment of the dog. Their approach, based on scientific principles within the discipline of animal behavior, which include learning, genetics, physiology, motivational analysis, etc., contrasts markedly with the approach utilized by dog trainers and other self-proclaimed animal behaviorists who portray themselves as experts. Many trainers continue to employ heavy-handed correction techniques. Harsh corrective techniques may make a dog fearful even to the point where he will retaliate with further aggression.

Factors influencing canine aggression

Reward and Punishment

The animal behavior literature is replete with examples which demonstrate that aggressive behavior is subject to the strengthening effects of reward. The phenomenon has been observed in a wide range of species ranging from Siamese an?ghting-?sh to monkeys.

Therefore, it is not surprising to ?nd a lowered threshold for aggression in a dog who has had several successful aggressive encounters; or in a dog who has been rewarded for aggression in the past. An obvious example is the attack-trained watchdog. One aspect of attack training consists of intentionally rewarding the dog if he responds aggressively after a command. With suf?cient training the habit strengthens and increases even to the point where the dog actively patrols seeking out stimuli to attack. Aggression thus develops its own self-reward properties. ln other circumstances a dog may be unintentionally rewarded for aggressive behavior. For example, a dog who is being walked on lead may growl at an approaching stranger. The concerned owner may then try to reassure the dog by saying it’s OK, while lightly patting him on the side.Literally speaking. the dog probably interprets the owner’s communication as meaning “it’s OK to growl.”

Or take the case of quiet little Fido who suddenly becomes transformed into a raging terror whenever a uniformed person approaches your property. His territorial inclinations tell him to protect your property. And, in most cases, he knows when he did wrong, and that if you get a dog to “respect” a trainer, everything else will fall into place. This militaristic approach is based on anthropomorphic reasoning. lt is not based on any theoretical understanding of the mechanisms controlling animal behavior.

These everyday examples. which are re?ective of two different kinds of aggression – instrumental and protective — illustrate the manner in which reinforcement may operate. ln summary. a dog can become more aggressive through his own aggressive behavior independent of his interactions with the owner. And. in addition, as the ?rst two examples illustrate, both intentional and unintentional interactions with an owner (or trainer) can strengthen aggressive responding. The opposite, however, is not necessarily true when punishment is applied. One cannot assume that punishment will suppress and/or eliminate aggression.

On the contrary, what punishment often does is to enhance the tendency to respond aggressively. Punishment translates into pain and pain is a primary eliciting stimulus for aggression? Further, repeated punishment might make a dog. fearful when exposed to those situations in which pain was previously experienced. Aggressive responding could then become elicited through fear. Surprisingly, very little information exists in the animal behavior literature concerning the effects of punishment on aggression not elicited via pain or fear; that is, aggression which is instrumental, territorial, protective, or learned in some manner. For these latter types of aggression, my experi- ence has been that punishment may be effective if it is judiciously applied in a timely manner.


At present there are 150 breeds recognized by the AKC. The variability in the proclivity for aggression that exists among the various breeds is tremendous. As we all know some breeds are “naturally” more ag gressive than others, although individual differences often mask whatever breed difference one would expect. My experience has been that breeds of dog which were ancestrally bred for protective or predatory func- tions (i.e. Shepherds, Mastiffs, Terriers tend to present more problems for certain kinds of aggression than breeds of dog that were originally bred for hunting or herding (i.e. Collies, Beagles, Retrievers). This is just a broad generalization, however. Reliable information,drawn from a large data base,still needs to be gathered on this topic. I refer the interested reader to the recent research of Borchelt for preliminary data.

Moreover, it is important to realize that selective breeding programs. as carried out by individual breeders. can readily increasetbe tendency for aggression in a particular line of dogs. In other words. the process of selectively breeding only the most aggressive individuals. This is obviously true for the American Pit Bull Terrier. Pit Bulls are remarkable in that some individuals (but not all) have been bred not only for their tendency to ?ght other dogs. but also possibly for a tendency to engage in a trait called “gamehess” – that is, the desire to continue to fight even when severely beaten. The fighting strategy,”he who fights and runs away, lives to fight another day” employed by other non-domesticated mammalian species, obviously does fit for some American pit bull terriers.

There is little doubt that many of the different kinds of aggression are in?uenced heavily by genetics. Probable examples are territorial aggression, various kinds and of protective aggression. and dominance aggression. These kinds of aggression have more natural programming built into the animal, and because of this many appear early during development. This contrasts with aggressive behaviors that are primarily learned. Dominant related aggression directed towards humans in some instances is an interesting example because ot the unintentional manner in which the trait may have been selected (and may still be) by breeders. For example, since purebred male dogs who are winners in the show ring are often the ones selected to do a disproportional amount of breeding. The behavioral traits (all dominance-related) whichi these top male show dogs possess (i.e. weight forward. tail-up. ears-up.; erect body carriage. etc.) are therefore ever greater likelihood of being transmitted to subsequent generations.


Accurate information concerning the effect hormones have on companion animal behavior is not readily available. For this reason, one often gets a variety of opinions concerning their in?uence. Published studies from the University of California. Davis indicate that castration usually affects behaviors which are sexually dimorphic; that is, behaviors usually found only in one sex, in this case the male. Four behaviour patterns were found to change in a certain percentage of dogs after castration; namely. inter-male aggression, in-house territorial marking, mounting the legs of humans, and roaming. The magnitude of the effect was found to vary from dog-to-dog (ranging from a 30% – 60% either on a long or short term basis). The reason for the variation can probably be attributed to unspeci?ed effects of past experience and the environment in which the dog was living. Also noteworthy was the fact that castration did not have an effect on most of the other different types of aggression (i.e. fear-related, territorial, possessive).

At present, there is still debate concerning the effects of castration on dominance aggression. Like Voith and Borcheltz l also believe that it may help mellow a dominant dog, provided this treatment is combined with concurrent behavioral modi?cation procedures. The mechanism through which castration works still needs to be answered: Some feel that the physiological changes brought about through testosterone depletion are responsible for the loss of dominance while others feel that any change (subsequent to castration) is the result of a altered interactional style on the part of the owner having known the dog has been ?xed.

Neutering a female probably will not affect the tendency for aggression and, in certain instances, may even increase the tendency. Generally, androgens have a facilifory effect on certain types of aggression (intermale; dominance-related) and estrogens have an inhibitory effect. This explains why females show less of a tendency to exhibit the types of aggression typically exhibited by males (i.e., dominance aggression). ln this regard, Voith and Borchelt note that the majority of females presenting problems of dominance aggression are individuals who have recently been spayed, a finding substantiated by other research workers.

Individual differences are marked when it comes to determining if hormonal supplementation will alter aggressive behavior. For males, one the administering of could try female hormone (e.g.synthetic megestrol acetate) on a temporary basis to get an approximation of what one could expect from castration. Occasionally both hormonal supplementation and castration are required to decrease aggressive responding, but the use of hormones to accomplish this has diminished greatly in recent years due to the potential of serious side effects. In recent years, in veterinary behavioral medicine, there has been a marked tendency to administer other kinds of drugs that have the potential for less serious side effects, such as Xanax,  Prozac, Buspirone, and amitriptyline.  Note, however, that many of these drugs have not yey been approved for veterinary usage.

Resource competition

Two dogs will ?ght if they are put in competition for a resource in the environment. Likewise. the dominant dog in a household will attack a subordinate dog if he senses the latter threatens his access to an environmental resource.The environmental resource most often implicated in competitive ?ghts are food, access to females in heat (in the case of males). and attention from the owners. Often competitive ?ghts have a greater chance of occurring in dogs who are relatively equal in status but they may also occur in dogs relatively far apart in rank. “Jealousy” ?ghts between dogs merit special attention. The ?ghts are usually savage in nature and l have found the problem dif?cult to treat. The ?ghts often show a pattern of occurring mainly at greetings – an occasion when each of the dogs are trying simultaneously to solicit the owner’s attention.

The cases l have treated have usually been female-female jealousy confrontations. Much less often I have handled male-male or female-male jealousy confrontations. Cases where a male will attack a female are much less frequent. A dog will even attack a human dog senses senses that the latter threatens a particular resource. As an example, I consulted an owner concerning her dominant male Chow who had who had severely attacked a visitor into her home. A case history revealed that the the dog’s aggressive potential happened in only one speci?c local— the kitchen near a particular cabinet. The kitchen cabinet area is where his food and treats were kept. One incidence was elicited when he owner’s friend (a stranger to the dog) made the mistake of actually opening the drawer containing the treats. The dog immediately attacked. Apparently, rather than anticipate that he was about to get a treat. the dog probably interpreted the actions of this person as a threat to his food resource (an example of food-guarding).

Veterinarians and animal behaviorists frequently deal with many owners  complaining about aggression in their dogs. Several surveys published in the literature indicate that undesirable aggressive behavior is the most common  behavioral complaint expressed by dog owners. I am hoping that this short review provides a better understanding of the phenomenon of canine aggression for the practicing veterinarian. l feel it would be a mistake to treat the factors in?uencing aggression in isolation from one another. A fundamental premise shared by most Ph.D.trained animal behaviorists, is that all behavior is the product of genotype-environme interactions. Aggression is no exception. Therefore, for any given case of aggression in a dog those factors responsible for the elicitation of the response probably operate in an interactive fashion. This obviously complicates the situation; nevertheless, it makes inquiry into problem behavi of companion animals all the more in intriguing for academically trained animal behaviorists interested in this branch of veterinary care.