There is a difference in a dog who is fundamentally aggressive by nature (very rare) and a dog who can show aggressive behaviours. Every dog has the ability to act aggressively at some point in their lives.
1. Medical issues
There are some diseases and disorders that alter a dog’s ability to think clearly and become aggressive. ‘Metabolic changes, organ dysfunction and neoplasia can all increase irritability, affect brain function, and reduce the threshold for aggression’ (Denenberg et al, 2017, p.19). Another condition is Canine Cognitive Dysfunction (CCD) which causes ‘anxiety and aggression’ (Prpar Mihevc and Majdič, 2019, p.604) in dogs. Additionally, L-2 hydroxyglutaric aciduria (L2HC) is a neurometabolic disorder known to be quite ‘rare’ (Bohm, 2016, p.543) but have symptoms of aggression. Thyroid issues can also lead to aggression as Bernal and Nunez (1995) and Vara et al (2002) concluded that thyroid hormones are part of the neurotransmitters involved in processing behaviours including aggression.
Another medical condition which can play a role in aggression from dogs was Neoplastic Brain Disease. This disease leads to tumours in the brain resulting in ‘direct invasion of the brain tissue’ (Denenberg et al, 2017, p.41). The consequence of these alterations to the brain, cause ‘behavioural changes’ including ‘aggression’ (Denenberg et al, 2017, p.41). Neoplastic disease symptoms are similar to Dementia including ‘head pressing… hyperactivity, aggression, lethargy, or attention seeking’ (Henderson, 2014, p.3).
Neoplastic diseases are also common in certain breeds such as ‘Bernese Mountain dogs (BMDs), rottweilers, and retrievers having a high prevalence with a frequency of approximately 25% in the BMD breed’ (Abadie et al, 2009, p.19). The reason for this is thought to be due to ‘the use of popular sires and inbreeding’ reducing ‘diversity’ (Abadie et al, 2009, p.26).
Therefore, it is important to seek veterinary advise for medical issues.
2. Fear Based Aggression
In most cases aggression is expressed by dogs as a last resort and most commonly due to fear and anxiety (Denenberg et al, 2017). Dogs who are in distress will react to try and cope with the trigger. Distress can cause a dog to act differently in many ways, however, aggression is notably more concerning for owners as owners are more likely to seek help for behaviours that are destructive and inconvenient (Overall, 1997). Normally a dog will communicate in subtle ways with body language or barking before reaching the point of showing aggression to irradicate the threat. The dog may freeze when scared or try to run away or bark, lunge, or bite to make the trigger go away (Rodan, 2010). This is known as the fear response ‘fight’, ‘flight’ or freeze (Steimer, 2022, p.2). The level of aggressive response to a threat from a dog will depend on their own past experiences of coping with the ‘triggers’ (Notari et al, 2022, p.594). Long term exposure to a distressed state of mind can lead dogs to use aggression as a coping mechanism regularly, rather than a last resort.
3. Selective Breeding
Dogs with exaggerated features could
resort to aggression behaviours quicker.
Dogs with no tails for instance may struggle to communicate through body language which is the main form of communication dogs’ use. The usual more subtle signs dogs demonstrate to leave them alone may not be possible due to the dog’s morphology. For example, dogs with excessive skin folds on their face may impact their ability to lift their lip (Goodwin et al, 1997) and show teeth as a sign of unappreciation of a threat and have to escalate to lunging and biting. Additionally, Fawcett et al, (2018, p.14) found that ‘short-skulled dogs are significantly more likely to show … dog-directed aggression’.
Dogs’ morphology has rapidly changed and the ones with the most exaggerated features can have a real impact on medical conditions they are more likely to have. The shape of the dog’s head can cause ‘neurologic disorder’ (Fawcett et al, 2018, p.10) which impacts their brain’s ability to function normally and cause aggression. Dogs with these exaggerated structures can lead them to suffer from medical conditions such as excessive skin folds, causing skin irritation and dermatitis (Asher et al, 2009), short faces causing brachycephalic obstructive airway syndrome (BOAS) (Packer et al, 2015) i.e., ‘restricted breathing’ (Fawcett et al, 2018, p.2), spinal issues to name a few which intern can make the dog more irritable and lead to aggression. Or dogs who need constant vet appointments or surgery to correct inherited issues like excess skin will take time away from the dog socialising and having positive experiences with the world.
Citations
Abadie, J., Hédan, B., Cadieu, E., De Brito, C., Devauchelle, P., Bourgain, C., Parker, H.G., Vaysse, A., Margaritte-Jeannin, P., Galibert, F. and Ostrander, E.A., 2009. Epidemiology, pathology, and genetics of histiocytic sarcoma in the Bernese Mountain dog breed. Journal of Heredity, 100(suppl_1), pp.S19-S27.
Bernal, J. and Nunez, J., 1995. Thyroid hormones and brain development. European journal of endocrinology, 133(4), pp.390-398.
Bohm, M., 2016. Why is L-2 hydroxyglutaric aciduria relevant for a general practitioner?. The Veterinary Record, 179(21), p.543.
Denenberg, S., Liebel, F.X. and Rose, J., 2017. Behavioural and medical differentials of cognitive decline and dementia in dogs and cats. Canine and Feline Dementia: Molecular Basis, Diagnostics and Therapy, pp.13-58.
Fawcett, A., Barrs, V., Awad, M., Child, G., Brunel, L., Mooney, E., Martinez-Taboada, F., McDonald, B. and McGreevy, P., 2018. Consequences and management of canine brachycephaly in veterinary practice: perspectives from Australian veterinarians and veterinary specialists. Animals, 9(1), p.3.
Goodwin, D., Bradshaw, J.W. and Wickens, S.M., 1997. Paedomorphosis affects agonistic visual signals of domestic dogs. Animal behaviour, 53(2), pp.297-304.
Henderson, H., 2014. L-2 hydroxyglutaric aciduria in a South African Staffordshire Bull Terrier. Journal of the South African Veterinary Association, 85(1), pp.1-5.
Hsu, Y. and Sun, L., 2010. Factors associated with aggressive responses in pet dogs. Applied Animal Behaviour Science, 123(3-4), pp.108-123.
Notari, L., Kirton, R. and Mills, D.S., 2022. Psycho-behavioural changes in dogs treated with corticosteroids: A clinical behaviour perspective. Animals, 12(5), p.592.
Overall, K.L., 1997. Pharmacologic treatments for behavior problems. Veterinary Clinics of North America: Small Animal Practice, 27(3), pp.637-665.
Prpar Mihevc, S. and Majdič, G., 2019. Canine cognitive dysfunction and Alzheimer’s disease–two facets of the same disease?. Frontiers in neuroscience, p.604.
Rodan, I., 2010. Understanding feline behavior and application for appropriate handling and management. Topics in companion animal medicine, 25(4), pp.178-188.
Steimer, T., 2022. The biology of fear-and anxiety-related behaviors. Dialogues in clinical neuroscience.
Vara, H., Martı́nez, B., Santos, A. and Colino, A., 2002. Thyroid hormone regulates neurotransmitter release in neonatal rat hippocampus. Neuroscience, 110(1), pp.19-28.
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