The first six months are the "main growth phase". They require high quality protein and nutrients.

The next 6- 12 months require a reduced protein content to help prevent any growth disorders.

Now fully grown, finding the right diet to match their energy requirements is key. 

Now in old age, diets with a lower fat and phosphorus are needed.

Sammy's Blog - New Balls Please

The humans seem tremendously excited at the moment about ballgames. Some of them are worked up about football - a game which is of limited interest to us dogs because it involves a ball which is too big to fit in the mouth -- how pointless! But other humans are in a flap about tennis, which we can all relate to since the tennis ball is high on the list of every dog's favourite toys. Humans, though, treat our favourite playthings in the most bizarre ways. As well all know, sticks and balls are for throwing and fetching (though perhaps not delivering back to the human, depending on how well "trained" one is...). But my humans get hold of a perfectly chewable tennis ball and - without even putting it in their mouths - hit it with a strange stick over a net to each other... back and forth. This goes on for ages, and when I try to get involved by fetching the ball and showing them how to chew it, they get cross and tie me to a chair. When they are finished with their strange pastime they usually put the balls away in a peculiar dog-proof tube, but the other evening the lid fell off while their backs were turned and I was able to give a comprehensive demonstration of how to savage a group of tennis balls to death. Were my humans grateful? Quite the opposite. Humans. eh? I'll never work them out. New balls, please...