[Jenn H]

In order to avoid nutritional deficiencies put your dog(s) on a rotation diet of high quality foods meant for their size, activity, age, etc.
The only reasons you would have to supplement their food is if they’re fed low quality food, you home cook for them, they need it temporarily (due to low quality diet or illness), have a health issue that prevents them from absorbing/producing that particular nutrient, etc.