[db7]

First, IMHO your dog doesn't look underweight from the picture you've shown. I can't see ribs for example. But that is just from one picture. So maybe he is too lean.

The simplest thing you can do to bring his weight up is increase the feed. It's better, in my mind, to do that than to add things like fat scraps etc. to the diet. Keeps things more balanced. For example, some have recommeded in the past to give a raw egg with the food as a boost but that will inhibit biotin intake. Bloat should not be a big concern if you do a few simple things. Limit water intake before and after the meal. Don't let him get excited or rolling and twisting around after eating. While bloat can be extremely dangerous if it happens, it is a small risk if you are careful. If you ever do see the signs go to the vet ASAP and insist on treatment including a radiograph to confirm if the stomach is twisted, don't let the vet guess. Timing is critical and quick response greatly reduces morbidity.

Recent studies show feeding two meals instead of one does not decrease risk of bloat.

You are feeding him a pretty good food. If you wanted you could try a food that is a bit richer. I think Eagle Pack Power is about the richest around, designed for working sled dogs, also used by lots of hunters/field trialers. I use tlcpetfood.com, it's in the middle between what you are feeding and the Eagle Pack. Eagle Pack original is pretty close to the TLCpetfood.

Another option is supplement with Prozyme which is a digestion aid. Will help him extract maximum nutrition from the food you are giving him.

Don't be too concerned if you are feeding more than the guidelines, particularly in the winter with a shorthaired dog. Dogs use food to regulate the body temperatures, so if he is active outside a lot he will require more food.