Forms of Aggression
Although types of aggression have been identified and neatly categorized here, the reality is aggression is not so neatly segregated. It is rare to see a dog with only one type, thus complicating the diagnosis and treatment. .
Generally the methods to treat aggression are:
Avoiding situations that provoke the aggression
Taining (behavior modification)
Pharmacological intervention (use of behavior altering drugs)
Surgical intervention (usually castration of the male dog)
Owner directed or "Dominance" Aggression
The most common and complex of category of aggression. "Dominance" aggression is somewhat misnamed, as it is about the concept of control. Truly "alpha" and confident dogs are usually quite tolerant of subserviant members of the pack. A dominant or pushy dog does not mean it is or will be aggressive.
Indications: growling, lifting a lip, snarling, snapping or biting directed primarily at family members or people (see Dog-On-Dog aggression) with whom the dog is familiar. The dog usually has conflicts with who the dog regardes being mostly closely ranked to him or her. It is both inherited and learned.
Approximately one in five aggression problems brought to a veterinarian are dominance related.  Generally the belief is the posture of aggression is a self confident one opposed to a submissive one (fear aggression). It tends to be in response to competitive contexts, dominant-appearing postures or interaction by the owner. However, dogs might be divided into two groups - those that know they are in control (less common) and those that are unsure of their social role and use aggressive behaviors to determine what is expected of them (more common).
Dominance aggression is the dog's problem and not caused by the response of the owner, although the owner could inadvertently encourage the inappropriate behavior to develop.
An association between territorial aggression and dominance-related aggression has been reported.
Things that could set off the dog:
Attempting to dominate the dog (staring at, punishing, etc.,)
Disturbing the dog while resting
Approaching while the dog is eating, playing with or near a valued resource or object, reaching for
Handling/touching the dog
Fear aggression occurs when the dog is scared whether or not an event has occurred that scared the dog. The difficulty for owners hearing this diagnosis, is that is encourages them to reassure the dog which reinforces the inappropriate behavior.
Initial behaviors can include:
Other behaviors may include:
changes in pitch and volume of vocalization,
snapping and biting if threat continues
possibly urination, defecation or anal sac expression.
Body postures associated with fear aggression include:
a lowering the the head and body (ears are often flattened)
ears moved back
horizontal then vertical lip retraction
These dogs try to avoid the situation by backing up until they are cornered, then they bite. This is in contrast to the normal dog who puts his tail between his legs, cowers, and hides when afraid, but shows no signs of vocal or physical signs of aggression. It is a learned behavior that can become habitual and continue even after the dog is no longer afraid.
Territorial or Protective Aggression
Territorial aggression is defined when the dog protects an inappropriate location as its territory, or an inappropriate location in an inappropriate context.
It presents as aggression to strangers when what the dog considers as the dog’s turf (owners, home, surrounding streets, car, etc.). is perceived by the dog as being threatened in some way. People in uniforms are a particular target. Can be friendly on neutral territory such as a veterinary clinic.
Protective aggression relates to the dog's perception that his owner is being threatened in some way. Its important to understand this is what the dog perceives, not what we perceive. Again, true protective aggression is when the dog reacts inappropriately and out of context when there is no real threat.
Both dominance aggression and fear-related aggression can be components or can be independently of the behavior. Generally speaking it is the intensity of the territorial or protective drive that is inherited, and is augmented through learning.
Dog-on-Dog Aggression Related to Dominance
Can be generalized or specific to situations. The dog is aggressive to some other dogs and displays both posturing (body held erect, tenseness, tail held up, eyes fixed on other dog) in the presence of other dogs and other signs of dominance at home (being overly confident or pushy).
It is considered abnormal behavior when the dog responds to another dog whether or not the dog is challenging or appears threatening in anyway. Additionally is is difficult to know if the dog is actually fear or territorially aggressive. Only a careful, context specific history can provide this.
Dog-on-Dog Aggression— Related to pack (sibling
Usually occurs with a known dog or between dogs living in the same household. It usually involves challenges for status. Challenges may involve access to resources (toys, attention, food), or may be more passive and involve posturing and manipulating the trajectory and behaviors of the other dog. Often occurs between dogs of similar age, or when the younger dog reaches social maturity. If the older dog refuses to give way, or neither can maintain sufficient status to win over the other dog, interdog aggression results.
A less common form is when submission of one dog is not enough to discontinue the aggression. To the extent that this aggression is considered abnormal depends on the intensity of the (potentially lethal)response to normal canine behaviors designed to resolve the conflict.
Dog-on-Dog Aggression Related to Fear
Can be generalized or specific to situations. This involves more-generalized aggression to all dogs or dogs of a certain breed or size. The dog’s history may be important (for example, aversive events may have occurred in the dog’s life). Posturing may be a clue, as for example if the dog backs off with its tails tucked. Many of these dogs respond well to the combination of behavior modification and pharmacological intervention (anti-anxiety medication).
Predatory Aggression related to small animals
Two types: Dogs that stalk, stare at or silently pursue small animals, (including dogs), and sometimes infants, and those who chase moving objects such as bicycles, etc., although some dogs exhibiting this behavior may be exhibiting territorial behavior. For example, dogs that bark and discontinuing the chase once out of the dog's territory is not characteristic of predatory behavior.
Stealth is an element of hunting behavior and is considered more dangerous since the intent is to kill. This problem can not be treated easily. However if there is a problem within the home with a baby or other pet, these dogs can go to other homes and not be euthanized. Predatory behavior with small animals does not guarantee the dog will react inappropriately with infants, but indicates the dog is at risk for such problems. These dogs should never be off lead, unsupervised, or confined in an area where other animals might cross.
Dogs that do not relinquish toys or objects to owners. If the owner tries to take the object the dog growls. Often the dog will present the object for play, and then strike when the owner reaches for the object. They may solicit attention and then respond to the attention with a challenge.
Aggression Towards Babies
Dominant, fearful and predatory dogs may all present a threat to babies and young children if they are not properly controlled. Dominant dogs often do not pose a threat until children reach toddling age.
Fearful dogs are most likely to be aggressive if they cannot escape the unwanted attentions of unfamiliar or seemingly obnoxious children.
Predatory dogs may pose a threat to newborn infants, but when the child can sit up, the infants often no longer elicit predatory responses from the dog.
Dogs may redirect aggression if interrupted in another aggression (i.e. dog-on-dog aggression). The dog may turn and threaten or bite the closest person or animal to them, who are often not involved. These dogs may be non-aggressive in the absence of the interruption of another threat.
However, if it is in response to an individual who was punishing or threatening to him then other aggressions types would have to be considered. It is possible that it could be part of dominance aggression.
Dogs react inappropriately to people or dogs around food. Generally the higher quality the food, the more pronounced the aggression. It can be difficult to treat because protecting food may be ancestral adaptive behavior.
When directed at people it may be an early indication of developing dominance aggression later in life. It easiest to feed the dog in an area that guarantees no disturbance. The behavior won't improve, but it won't worsen. Some behavior modification can be beneficial, but anyone who doubts their ability to execute desensitization around food should avoid it. Free feeding is not recommended.
Barking, growling or snapping while playing. A play growl is different from a serious one. True aggressive growls are lower pitched and prolonged. A play growl is usually high-pitches, short, and repeated frequently. Changes in the pitch may happen too quickly to safely detect.
Puppies that have not been exposed to other dogs often to other dogs may play inappropriately, or may play inappropriately because the owner encouraged rough play. Some play aggression is the result of abandonment, lack of interaction (in a shelter for example), or restricted access to other dogs in a normal play situation.
A female protection of her litter, or even toys or possessions during false pregnancy. This can appear to be competitive aggression however it is hormonal based. This aggression only lasts two months during the false pregnancy stage or longer if there is an actual litter produced. It can frequently occur with out a threat display.
However, some hormonal imbalances can cause abnormal maternal behavior that requires treatment with medication, and is particularly important to seek help from your vet if the mother dog injures her pups. Spaying reduces maternal aggression.
Health Related Aggression
The health of a dog can be a big factor a dog’s behavior (see aggression related to seizures, pain, old age, and medications below). Always talk to your vet first about your dog’s aggression. See medical issues of aggression for greater detail.
Some diseases causing aggression could be Hyperadrenocorticism (Cushing's disease), hypothyroidism, diabetes mellitus, brain tumors, cognitive dysfunction. Increased aggression around food and an increased appetite could be related to hormonal diseases.
Seizure Related Aggression
Caused by seizure-like brain disorders. Directed toward anyone or anything. Indications– violent, uncontrollable aggression is elicited by trivial stimulus. There is a pre aggression mood change, which last for minutes or hours before an attack and a post aggression depression with reduced responsiveness. It is sometimes associated with compulsive behaviors, such as self-licking or snapping at imaginary flies. See medical issues related to aggression for greater detail.
Pain Related Aggression
Response to illness, injury or chronic pain, such as underlying medical problems such as painful muscles, joints, and teeth, an uncomfortable gastrointestinal system or neurological problems. Aggression can be toward nearest human or animal.
Aggression Related to Old Age
The loss of hearing or sight can cause a dog to be caught off guard, resulting in aggression. Also a dog may have some health issues (also see Health, Pain and medication related aggression).
Aggression Influenced by Medications
Always check with your vet if your dog is taking any medication to see if the medication could contribute to aggression, or if the aggression may be a reaction to the medicine. Some common medications that can contribute to aggression: Phenobarbital (required medication for seizures, Prednisone or other corticosteroids.., NSAIDs, including Rimadyl
**Aggression categories complied from:
Clinical Behavioral Medicine for Small Animals, Karen L. Overall, M.A., V.M.D., Ph.D. Diplomate, American College of Veterinary Behavior, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia. Pennsylvania, Mosby, Inc. 1997
The Dog Who Loved Too Much: Tales, Treatments, and the Psychology of Dogs, Dr. Nicolas Dodman, BVMS, MRCVS, Bantom Books, 1997
Special report, Cornell University College of Veterinary Medicine Animal Health Newsletter by Cornell University College of Veterinary Medicine Animal Health Newsletter 53 Park Place, new York, NY 10007
 The Dog Who Loved Too Much: Tales, Treatments, and the Psychology of Dogs, Dr. Nicolas Dodman, BVMS, MRCVS, Bantom Books, 1997
Canine Aggression: Neurobiology, Behavior and Management, Ilana R. Reisner, DVM, Phd, DACVB, Orgiginally posted on :http://www.vetshow.com/friskies/cani.htm
Thanks very much to K9 Aggression.com for this wonderful article!