Identifying sudden aggression triggers in dogs

When a normally mild-mannered dog suddenly displays aggressive behaviour, what are the causes?

"Sudden onset of aggressive behaviour in dogs is the result of interactions between many complex factors caused by genetic predispositions, hormones, age, sex, reproductive status, breed, environment, early experiences, later learning, behavioural issues or medical conditions," says Rosemarie Tang, a certified professional animal trainer and behaviour counsellor.

Getting a vet to eliminate possible and potentially serious medical conditions as the cause is the first step, as there is an urgency to treat a health issue sooner than later. If medical causes are eliminated, the next step is to look at the most common behavioural causes.

One of those is pain-elicited aggression. Tang says: "Even a friendly, well-socialised animal may bite if injured or in pain. Inflicting pain [unintentionally, such as when treating a wound] always creates the serious risk of making the animal aggressive."

She adds that it is one of the most common reasons for sudden onset of aggressive behaviour in dogs that have not previously displayed any signs of aggression. Depending on the cause, the pain may be treatable or at least manageable.

Fear-motivated aggression occurs when a dog becomes intimidated and is defending itself. "Identifying and managing the triggers of your dog's fearfulness may be helpful in reducing aggression. When it's not practical to do so, then systematic desensitisation will be an excellent method to help make the dog feel less fearful," Tang says. Desensitisation involves exposing the dog to whatever it is that previously evoked its fear or anxiety, but at a distance and intensity that does not produce a response. In this case, it is best to work with an experienced trainer such as Tang. Your vet may be able to provide some recommendations.