Until your puppy is fully physically developed (about 18 months depending on breed) he is growing at a much quicker rate than small/medium breed dogs. Such rapid growth puts stress on bones and joints. Growth which is too fast can cause malformation of the skeleton and joints, and this will lead to pain and mobility problems in your dog's adult life.
Large breed puppy food is designed to give big dogs a controlled rate of growth to reduce the chance of such problems occurring.
Small breed dogs require more calories per pound of bodyweight than large breed dogs. Large breed dog food provides a controlled intake of calories, reducing the chance that your dog will become overweight or obese. Even a little excessive much weight on a large dog's frame can put stress on joints and the skeleton, resulting in pain and mobility problems.
What to watch for - ingredientsFor controlled growth, it is important that your dog's food have a calcium/phosphorous ratio of 1:1.2. Quality foods will indicate this ratio on its packaging/web page.
Good large breed foods also include joint support supplementation with ingredients such as glucosamine, though you may want to consider bolstering this with additional supplementation as they tend to be in small concentrations.
See our products pages for links to food and supplements which meet these standards.