I have a particularly large Labrador in the 40kg+ range, not fat just bigger than normal.
He is allergic to dust mites, rice and what I think is the 'E' number that makes yellow in those commercial dog foods. This led me to try and find a healthy diet without paying over the odds for it. Hard to do because the manufacturers really know how to hit you when your dog is ill.
Anyway I found Wainwrights which is a Pets At Home only brand. It is full of ingredients that you can actually say and you know what they are just at a glance, my dog uses the Senior Salmon & Potato. No 'E' numbers in it and no funky chemicals either. He has been so healthy since starting this food. He gets some raw steak, steak mince, prawns and fish for treats. He also gets a 1000mg cod liver oil capsule at night for his skin and coat.
After having two dogs in a row allergic to food items and having to find special diets both times which involved lots of reading and searching, I now advise people to stay away from the normal commercial brands such as Pedigree (Mars company) and Purina. It is akin to feeding your kid MacD's daily with the amount of chemicals and 'E' numbers they contain.
You can find a good diet if you look hard enough. Nutritious and junk free food is out there, you just have to look a bit harder than normal.
Just thought I would share for people who want a healthy diet for their dogs but don't want to go to a raw diet.