Canine aggression is the reason for 70% of vet referrals in North America. An aggressive dog can exhibit a range of behaviors including a warning snarl or growl, lunging, baring teeth, snapping, nipping, and biting. All of these behaviors are signs of some kind of distress.

Aggression is not an illness in itself, but a sign of some difficulty the dog is experiencing. Because it is unacceptable and dangerous, for both the dog and the object of the aggressive behavior, it’s imperative to find and treat the underlying cause.

Dogs are aggressive for either behavioral or medical reasons. Any condition, illness, or disease that causes pain can lead a dog to act aggressively.

Behaviorally rooted canine aggression occurs when a dog is attempting to use aggression to remedy a social situation which it finds unacceptable. An aggressive dog may be defending its territory, possessions, food, or pack members—including its human family—from a perceived threat. Behavioral aggression can also stem from fear, frustration, or the dog’s attempt to retain its place in a social hierarchy.

Orthopedic conditions relate to the dog’s skeletal system, and can be very painful, leading to a dog’s defensive aggression.

Hip dysplasia is a kind of osteoarthritis which is genetically related, and is more common in such larger breeds as Bulldogs, Mastiffs, St. Bernards, and Retrievers of all kinds. Diet and exercise are also factors in the development of hip displasia. Cruciate ligament rupture is a tear in the middle of a dog’s ligament which typically results from some kind of trauma to the leg, leading to lameness and pain. A luxating patella is hereditary, can involve deformities of the hip joint and leg bones, and results in lameness or an abnormal, skipping walk. Disc disease results from degeneration, then abnormal protrusion, of discs between the dog’s spinal vertebrae. This can lead to a compressed spinal cord, spinal nerve, or nerve root.

Decline in a dog’s cognitive function is associated with age related degeneration, including loss of hearing and sight, disorientation, sleep irregularities, and loss of control of elimination. This can lead to confusion, anxiety, insecurity, and fear, to which a dog may respond with aggression.

In hypothyroidism, the thyroid gland produces less thyroid hormone than normal. Signs include increased body weight, lethargy, hair loss, and aggression, with varying degrees of dysfunction. The most common causes of hypothyroidism are lymphocytic thyroiditis, idiopathic thyroid gland atrophy, and brain tumor.

While there can be many causes of neurological problems in a dog, any neurological problem can lead to behavioral abnormalities, including aggression.

A dog who has suffered from an epileptic seizure will often be more aggressive just after the seizure, as it is not yet in a normal state, and lacks full awareness. Sudden aggression with no apparent provocation can result from a seizure in a part of the brain that controls aggression. This is more likely to occur in Spaniels, Retrievers, Bull Terriers, and Poodles.

Because aggression can stem from either medical or behavioral causes, a veterinarian should always be immediately consulted to assess any possible medical problems. Even if there is a medical cause, aggressive behavior will involve some level of learning, so behavioral causes always must be addressed through training.

While cognitive dysfunction syndrome can be a normal and irreversible result of aging, its effects can also be treated through environmental enrichment, several medicines, natural diets, and supplements that can improve cognitive functioning. A veterinary consultation is necessary to undertake the proper course of therapy. 

Orthopedic conditions, hypothyroidism, and neurological problems are more serious medical conditions, and can require an extensive course of treatment. Orthopedic conditions commonly require surgery, but can be controlled or improved by reducing the dog’s weight to decrease pressure on the dog’s joints, reducing joint impact by reducing exercise on hard surfaces, physical therapy, and the administration of anti-inflammatory drugs and joint fluid modifiers. Dogs with hypothyroidism must be administered thyroxine, a thyroid hormone replacement, under veterinary supervision. 

Head trauma requires emergency care, in which the dog’s breathing, circulation, and nervous system will be examined and stabilized if necessary. The dog may be in shock, and could need oxygen, pain medication, and control of its breathing. Brain tumors require surgery. Hydrocephalus is treated with corticosteroids, though more severe cases may require surgery. Encephalitis requires antibiotics, followed with supportive care, including fluids, nutritional supplements, and physical therapy. Epileptic seizures can be treated with anticonvulsant drugs. All of these causes of neurological problems are very serious, and require immediate veterinary treatment.

Careful attention to a dog’s physical condition and social environment can alert you to any early signs of aggression. An aggressive dog’s behavior requires lifelong management. Behavioral aggression is easier to avoid than aggression due to medical causes. Take care to make your dog feel secure with its position in the family, territory, possessions, and food. Avoid unnecessary attempts to control your dog’s behavior, such as disturbing the dog when it is resting or taking away its food or water. Monitor aging dogs carefully for signs of cognitive or physical dysfunction or impairment. 

Genetically related orthopedic conditions, brain tumors, and most neurological problems are not preventable, but early awareness can lead to earlier treatment and more effective resolution of symptoms. Of course one should always take care to keep one’s dog safe and out of harm’s way, avoiding any kind of physical trauma whenever possible. Provide a fenced yard, and keep your dog on a leash when away from home.

Treatment cost can vary depending on the cause of aggression. Hip dysplasia treatment costs an average of $2500, while hypothyroidism costs an average of $1300 to treat. The average cost of treating epileptic seizures is $3000.