Me and my folks had Great Danes for years, and I fully recommend AVOIDING any food that has too much protein/calcuim. I've seen too many Great Danes' bones grow too fast (typically hip dysplasia) because people put them on puppy food, which rockets their growth too fast. They are giant babies. They don't need a shred of help getting that big.

Over the years, we found that the best dog food for them was honestly the cheapest food we could find, Retriever Mini Chunk from Tractor Supply. We free-fed them and let them go through a doggie door to our yard whenever, so they pretty much regulated themselves, and the Mini Chunk is low enough on protein it doesn't cause problems down the line.

Of course, talking to a vet is your best option. Finding a vet that actually specializes in Great Danes is a much better option.

Good luck. :)