09/29/2026
Aggression isn’t always a purely behavioural problem. Sometimes, an underlying medical issue may be contributing to the behaviour.
A 2026 paper described two dogs with intrahousehold aggression in which physical discomfort, including pain, was considered the primary motivational factor.
𝗖𝗮𝘀𝗲 𝟭: 𝗧𝗵𝗲 𝗪𝗲𝗹𝘀𝗵 𝗧𝗲𝗿𝗿𝗶𝗲𝗿
A 7-year-old neutered male Welsh Terrier developed aggression toward people in the household at around 5 years of age, following an episode of illness.
The behaviour included fixed staring, growling, lunging and skin-puncturing bites. The owners also reported a slow, stiff gait, reluctance to continue walks, disturbed sleep, leg cramping and a depressed facial expression.
During examination, the dog looked toward its hindquarters during abdominal palpation, and an impacted a**l gland was identified. Because physical discomfort was suspected, a**lgesic treatment was started while further medical investigation was pursued.
The aggression decreased directly after a**lgesic treatment was initiated. Subsequent radiographs revealed severe osteoarthritis of the spine. Interestingly, the aggressive behaviour could resurface on days when the owners observed signs of pain.
𝗖𝗮𝘀𝗲 𝟮: 𝗧𝗵𝗲 𝗙𝗿𝗲𝗻𝗰𝗵 𝗕𝘂𝗹𝗹𝗱𝗼𝗴
A 6-month-old intact male French Bulldog began showing aggression toward another dog in the household at 3 months of age, after falling from a chair and injuring his right hind leg. The aggression subsequently increased in frequency and intensity.
The dog displayed fixed staring, a tense posture and biting directed mainly toward the other dog's face. Later, aggression could also be redirected toward owners who intervened.
Although initial radiographs after the fall showed no abnormalities, later examination revealed an abnormal hindlimb gait, hindquarter muscle asymmetry and signs of pain. Further orthopedic assessment found a positive Ortolani test bilaterally, and radiographs confirmed bilateral hip dysplasia, along with bone changes in the left proximal tibia.
After a**lgesic treatment was adjusted, the behavioural problem decreased. The dog subsequently underwent bilateral 3DHIP surgery. Six weeks later, the owners reported that the dog was doing well, was no longer receiving a**lgesic medication, and that the aggressive behaviour had disappeared. No behavioural retraining was necessary.
𝗪𝗵𝗮𝘁 𝗱𝗼𝗲𝘀 𝘁𝗵𝗶𝘀 𝗺𝗲𝗮𝗻 𝗰𝗹𝗶𝗻𝗶𝗰𝗮𝗹𝗹𝘆?
Pain can influence behaviour through avoidance of potentially painful interactions, increased irritability and reduced frustration tolerance. Importantly, the trigger for aggression may not always be an obvious painful stimulus.
The authors highlight several behavioural red flags that should prompt consideration of physical discomfort:
• A sudden change in behaviour, particularly following illness or injury
• Aggression associated with movement or approach
• Behavioural episodes without an obvious external stimulus
• Concurrent subtle signs of discomfort, such as changes in gait, posture, sleep or activity
• Behaviour that does not fit the dog's previous behavioural history
The authors also emphasize that medical and behavioural assessment should work together. Pain relief may resolve the behaviour in some cases, but learned associations with previously painful situations can persist and may still require behavioural intervention.
Study cited in the comments:
