I am very pleased with Zignature Whitefish kibble, I don’t know if Zignature makes a large breed puppy food, but if you go to their website they tend to answer questions promptly.
The food is not cheap, but then neither is going back and forth to the vet.
Sometimes it is worth it to pay a little bit more.
Regarding grain free diets, hope this helps:
https://www.mspca.org/angell_services/choosing-the-right-diet-for-your-pet/
excerpt below:
Grain free diets have become all the rage in the last few years. I suspect this has stemmed from greater recognition of gluten sensitivity in humans. Most pet food companies have jumped on the band wagon following the marketing success of grain free human diets. The truth of the matter is that there are no dog or cat studies showing a health benefit to grain free foods. A myth has been perpetuated that grains are unhealthy. In fact, whole grains contribute vitamins, minerals and essential fatty acids and are highly digestible by dogs and cats. Allergies to grains are actually very rare, and only the Irish Setter breed has been demonstrated to have a gluten sensitivity. Many grain free diets substitute potatoes and tapioca, which have less protein, more sugar, and less fiber. And typically these come at a higher cost.
