A recent study of nearly 45 hundred dogs linked stressful events during puppyhood to aggression and fear later on.

Pet parents used a validated questionnaire to report their dog’s history and behavior. Higher scores meant stronger fearful or aggressive responses to common triggers.

A third of the dogs had experienced trauma, such as physical abuse, surrender to a shelter or serious injury. Compared to those that faced adversity later in life, dogs exposed before six months of age scored higher on fear and aggression scales. Behavioral responses to the same triggers also differed from one breed to another, showing that genetics and environment interact to form a dog’s behavior.

Even with dogs that have a rough start, loving care, individual training and environmental enrichment can help with behavioral issues.