Great Danes can develop hip problems as they age. It's best to have a Great Dane puppy certified free of hip dysplasia before purchase or adoption. The dogs are large and need to be well trained and exercised regularly. Even healthy and well cared for Great Danes have a comparatively short life span of 7-10 years.
Because of their size great danes are prone to a few health issues. Large dogs tend to have leg and hip problems as well as heart and other issues. This does not mean there not good dogs it just means they require more visits to the vet than usuall which means they can be costly.
Large breed puppies like great danes and mastiffs require a special diet. Your mastiff / great dane puppy should only be fed a high quality ADULT DOG FOOD or a GIANT BREED PUPPY FOOD. Do NOT feed your puppy a regular puppy food.