Aggressive behavior in dogs & canines: Causes
This article published by Dr. Polsky first appeared in the journal entitled Veterinary Practice Staff in 1991, and has been revised for publication on this website.
Throughout my career as an animal behaviorist, I've always had a strong interest in studying the natureand causes of aggression in animals. My interest in aggression started soon after reading the late Konrad Lorenz's influential book On Aggression in the late 1960s, and it continued unabated through my doctoral studies at the University of Leicester, England. My doctoral research examined predatory aggression in a variety of mammalian species, particularly rodents. Today, as a practicing applied animal behaviorist serving pet owners in the Los Angeles area, my interests have moved from the laboratory to the owner's home, and occasionally in the courtroom, and the species I now study are pet dogs and cats.
And, as it turns out, my interest in animal aggression is well justified: as professionals in veterinary care know, aggressive behavioral problems, whether it be aggression displayed to the owners or to other pets, are very common. Moreover,animal aggression,especially when it's directed to children. is a behavioral problem that frequently leads to euthanasia for the pet.
In this brief overview, I focus on several variables known to have a strong causal influence on the display of aggression in companion dogs. For the sake of illustration, I will focus on one particular type aggression, namely, inter-male aggression, and discuss how the chosen variablea influence its expression.
Proximate causal factors influencing asgression in dogs may be grouped together in four broad categories: hormones, environmental influences, learning, and genetics. Significantly, one most importantly realized that these four categories do not act in isolation from each other. All work together interactively to affect aggressive responding, in rather than in an additive fashion.
HORMONES
Androgens, the collective name for the principal male hormone which includes testosterone, usually has a marked facilitative effect on the expression of inter-male aggression in most dogs. In contrast, progestins, the collective name for the principal female hormone, which includes estrogen, have a marked inhibitory effect on inter-male aggression. inter-maleaggression usually first appears in male dogs between approximately 9 and 16 months of age, but this is a general guideline and exceptions readily occur. Age of onset for this type of aggression correlates well with the onset of sexual maturity, and the increased levcl of endogenous testosterone not only motivates a male to behave like a male, but they also affect how a male is perceived as a male by other dogs. Castrated males, lacking most endogenous testosterone, smell different (at least to other dogs) and, therefore, are less likely to be reacted to with male-like behavior from other dogs.
The practical implications of this are clear: Castration frequently lessens fighting between male dogs. Conversely, the supplementation of a female hormone, such as depo-provera, or perhaps some of the newer medications such as the tricyclic antidepressants, or drugs like prozac, administered to a male dog, may also act to suppress male-like behavioral tendencies, but again the results vary depending on the past experience of the individual dog, and a host of other factors. Obviously, complexity operates determining the causation of dog aggression, thereby making it difficult to single out one causative agent in itself, but one can usually speak of major contributors relative to other factors in the causation of a dog's aggressive response.
Owners who are ambivalent about the castration, may first try to"chemically" castrate their dog through the administration of the female hormone,But it should be realized that the administration of certain hormones on a long-term basis may have undesirable side effects, and so in recent years the veterinary profession has almost completely avoided their usage in behavioral therapy regimes. Nevertheless, the administration of a female hormone will probably chemically suppress endogenous testosterone output and, thus, it may mimic the effects of castration. Clinical studies supporting this belief do not exist, however. It should be you still largely as experimental. Nonetheless, if tried and if this procedure is effective, then an owner, particularly men, may be more accepting about the castration procedure.
ENVIRONMENT
The feedback a dog receives from an owner significantly affects thc tendency to display aggression. Styles of feedback from the owner very tremendously. On one hand, there is the owner who seriously tries to discourage aggression by applying some kind of punishment agent (the kinds of punishment vary tremendously, and must be applied in a judicious matter to avoid serious side effects), and this contrasts markedly with the owner who permits aggressive displays to go unattended (e.g. the over permissive owner).
On the other hand, if punishment acts to suppress aggression, then the opposite, reward, should strengthen aggressive responding. This happens, for example in dogs who are taught to display aggression upon command (e.g., attack-trained dogs), or dogs who arc encouraged by owners to display aggression whenever a stranger approaches their property.
On a clinical note, owners who desire to reduce the tendency for aggression should obtain a dog as a puppy and discourage all signs of aggressive responding as soon as they are observcd. Veterinarians and their support staff, should encourage owners to start basic obedience training at a very early age (10 weeks) for most breeds: starting at an early age far outweighs the risks that might be assumed from contracting some sort of disease transmitted from another dog (e.g. parvo-virus). Obedience training and temperament training, provides the necessary socialization needed to other dogs and people, thus giving an owner assurance that the feedback a puppy receives will be sufficient to curtail subsequent aggressive responding as the dog develops and integrates itself into the human household.
LEARNING
The competent animal behaviorist knows that aggression in itself, especially if it's successful, is often self-reinforcing to an animal. That is, after several successful "wins", an animal becomes motivated to fight simply for the satisfaction of fighting. The principle of self-reinforcement for aggressive responding was first demonstrated in laboratory rodents many years ago, and subsequently it has been shown to occur in a wide variety of both vertebrate and invertebrate species, and it is readily demonstrated in a wide variety of circumstances in dogs, which includes the conditioning of a dog to engage in dog fighting.
GENETICS
Behaviors, like the physical features of a dog, such as its coat color are always affected to some extent by hereditary influences. Agressioa is no exception. Thus, one cannot escape the conclusion that certain breeds or more prone to display certain kinds of aggression when compared with other breeds. It would be foolish to dismiss this fact and assert, for example, that German shepherds or Chows are generally less pugnacious than Golden tetrievers with respect to certain kinds of aggression. German shepherds and Chows are what they are because of many years of selective breeding for particular behavioral tendencies.
CONCLUSION
A dog's hormonal level, its past experiences, and the feedback it receives from the owner all combine in an interactive fashion with genetics to produce a dog who is
more likely or less likely to respond with aggression in a given set of circumstances. Circumstances, however, vary from moment to moment; therefore, it may be difficult
predict with certainty the likelihood of an aggressive display at any given point in time, and in any given set of circumstances. For the most part, the complexity and the interactive nature of the factors causing aggressive responding in dogs prevents one from proffering simple explanations about this phenomenon.
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