While dogs can and do live on vegetarian diets, you should consider what a dog or wolf would eat in the wild. Their preferred diet would certainly not be soybeans and tofu! Dogs are carnivores, and their systems process meat most efficiently. Vegetarian diets largely contain soy to boost the protein content. Some dogs are allergic to soy, which can cause gastric upset. Most vegetarian dog foods are also low in protein and fat. If you work your rottie, you may have a difficult time finding a vegetarian diet with protein high enough for his needs. In this case, you may have to switch to a meat-based diet anyway. If your rottie is allergic to meat, consult your veterinarian.