Sorry, breed specific goes on the basis that all dogs were bred in different countries and for doing different jobs. So they would have ate different diets.

For instance labradors, coming from canada, ate lots of fish, then in england, game birds and rabbits etc, GSDs being a pastoral breed would have been mainly fed a diet of beef, they also have shorter colons than most breeds, meaning they need more fibre to slow down the faeces through the digestive system. A lot of GSD suffer loose motions, this is one of the causes, that can be altered easily.