Canine aggression, defined as excessive, unexpected or inappropriate barking, lunging, growling or biting directed at other dogs or humans, is a common reason for elective euthanasia at animal shelters and veterinary clinics.
Aggression in dogs results in significantly shorter lives in affected breeds and represents both an animal welfare problem and a public threat. Over four million dog bites are recorded in the USA annually, with severe disfigurement and fatalities less common, but particularly prevalent in young children and the elderly.
Dogs which are responsible for vicious aggression are often owned by people with reduced awareness of the implications of canine aggression, significantly higher criminal thinking, entitlement, sentimentality and superoptimism tendencies. Vicious dog owners are also more likely to themselves be arrested, engaged in physical fights or used drugs more than other dog owners.
Interdog aggression often involves same-sex pairs and is triggered in households relating to feeding times and owner attention.
Post-traumatic stress disorder in humans appears to have a canine corollary, particularly after specific traumas, physical separation from a bonded owner or following natural disasters.
Aggression toward unfamiliar dogs and people is a common problem arising most commonly from fear and territoriality. Dogs with more-aggressive behavior, especially social conflict-related aggression directed towards family members, show higher cortisol levels compared with non-aggressive dogs. For example, dogs introduced to shelters usually show elevated cortisol levels for the first three days, followed by a comparatively fast decline.
Testosterone, a critical androgen involved with aggression, results in changes within the basolateral nuclear group of the amygdaloid body that may trigger increased impulsivity associated with inappropriate aggressive behavior.
Impulsivity correlates with a decreased ability to tolerate delay of reinforcement due to testosterone's effect on disturbing natural serotonergic balances, resulting in imbalances between the amygdala, frontal cortex, hypothalamus and parietal cortex, leading to lowered serotonin and dopamine levels and consequent impaired cognitive regulation of impulsivity responses.
Aggression is a particular inter-dog and dog-human problem in stray dogs, and apart from the physical harm incurred and risk of permanent physical injury or death to other dogs, pets or humans, can also result in transmission of zoonotic diseases such as rabies and bite wound associated infections such as Capnocytophaga canimorsus.
Aggression appears to be related to rearing practices, rehoming, being acquired from a shelter, physical or psychological abuse by owner, lack of socialization, territorial issues, underlying diseases, increasing age and use of positive punishment/negative reinforcement training techniques.
Underlying diseases which can cause overt aggression include underlying painful disorders such as osteoarthritis, hip dysplasia, rabies and neurological diseases such as seizures, arachnoid cysts and hydranencephaly.
In cases where untoward aggression to either the owner of family members is a primary complaint, use of neutering, training, dietary protein restriction, additional of polyunsaturated fatty acids and prescription of drugs such as fluoxetine, amitriptyline, clomipramine or medroxyprogesterone acetate is indicated.
A realistic approach should be adopted when assessing individual cases, based on the degree of aggression and the risk of re-offending by an aggressive dog and deciding whether to surrender a dog or attempt interventionist therapy.
Training methods employed include gradual desensitisation and counter-conditioning techniques, which have variable success depending on the trainer's skills.
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