That’s a very good question and not an easy one to answer! Technically an animal couldn’t develop a mental disorder as the way we diagnose them is tailored towards humans and so it isn’t possible to use the diagnostic criteria with animals. However, animals have been shown to experience stress and emotions and to show things often termed depressive-like symptoms. As such, they are often used as models of human mental illness. In terms of clinical treatments for animal mental health issues, although antidepressants could be used in animals, often things like environmental enrichment are used to alleviate issues with an animals mental health.