Good question! Although it is debated in the field whether animals can develop actual mental disorders they can certainly show symptoms (e.g. depressive-like symptoms) and behave negatively in response to adverse experiences. We don’t know for sure what causes mental disorders, but trauma and stress are known to be risk factors for mental health issues and we know that animals show similar stress responses to humans. Additionally, we know that in many mental disorders in the brain there are chemical imbalances, though it could be that trauma leads to these imbalances.