Larger breeds of dogs in general are more prone to hip dysplasia which is why responsible breeders evaluate their breeding stock's hips after the age of two and prior to breeding. (picards.us)
Not only do you need to consider the basic nutritional requirements for dogs in general, but you also have to think about the specialized nutritional needs of senior dogs. (pawster.com)
That is also why I appreciated the section on responsible dog ownership and how you should have experience with dogs in general before adopting a large breed pet. (caninejournal.com)