German shepherd owners?

GERMAN SHEPHERD OWNERS! I have a three year old, 107lb GSD. I do
walk him daily or I will be ambushed and we play about 20 minutes of fetch.. My question is how much should I be feeding him? He seems to be gaining weight and I do not want him to get overweight because of my fear for hip dysplasia. I correct him to sit straight and not on any side. My GSD is twice his Dads size he is the biggest of all pups. Thanks. Also how many treats

It depends on what you're feeding him. All dog foods aren't the same. Look on the bag to see if there's a recommendation like so much food per pound of the dogs weight.

I wouldn't go by how he looks. Dogs with a thick coat look fatter in the Winter. If you are unable to weigh him, put your fingers into his coat on his ribs and go by that feeling to gauge whether he's fat or not.