What most naturally follows?

How to feed your senior dog a healthy diet
Determine when to begin a senior diet.
Consider your dog as an individual when deciding if it might be time to switch to a senior diet. Different dogs may benefit from senior diets at different ages.
Additionally, there is no formal definition for what constitutes a senior diet, so these diets will vary by manufacturer. Generally, a senior diet will have altered protein content, lower phosphorus, and reduced caloric content.