I use Burgess Supadog Lamb & Rice for sensitive stomachs. It really suits my GSD.
Burgess Supadog - Sensitive | Quality Dog food | Burgess Pet Care

Supadog Sensitive is great for all adult dogs, but is particularly suited to dogs with a sensitive digestion. The recipe is free from wheat gluten, maize, eggs, beef and dairy products. Rice is the main carbohydrate for energy and beet pulp aids healthy digestion. British lamb is the essential muscle building protein. Nutritional Values
Fibre 2.5%
Protein 20%
Vitamin D3 * 1,800 iu/kg
Vitamin E * 70mg/kg
Copper ** 10mg/kg
Vitamin A * 12,000 iu/kg
Oils & Fats 10%
Ash 10%
Ingredients

Lamb Meal (min 26%), Rice (min 26%), Beet Pulp, Poultry Fat, Salt, Vitamins.