Loki is always very thin, he must have the metabolism of a hummingbird because I just can't keep any meat on him at all.

Normally this is fine but this winter he seems to really be having a hard time with the cold.

He goes outside to potty and comes in and shivers enough that we snuggled him up under a blanket with us. Granted it was really cold and wet and snowing, but 5 minutes outside should not make him that cold.

I am feeding him three 24 ounce cup fulls of food a day, two of Chicken soup for puppies and the third Blue Buffalo grain free.

I have considered adding some hamburger and rice to his diet, or maybe some canned food, or another meal, or more food at each feeding?

He has been checked by the vet and his bloodwork was fine, he has no parasites but the vet agrees he could use another 5 lbs at least.

He does have a very thin coat too, with no undercoat, so I think I will try to find him a jacket this afternoon to help keep him warmer for now.

How old is Loki? Adult, right?

Puppy food is NOT appropriate food for adult dogs. The calcium/phosphorus and protein ratios are way off. I don't even feed puppy food to puppies once they start teething. The nutrition in it is designed to support skeletal growth. (I know you were thinking that it is more calorie-dense, which it is, but I think the mineral and protein balance is what you should be more concerned with).

I seem to recall that some brands of food have a "high-energy" or working dog formulation.

In addition, you could feed satin balls. They are great for putting weight on neglect/abuse victims that come into rescues and shelters.

http://www.doglogic.com/recipes.htm

Here are some other weight gain recipes
http://www.holisticdog.org/Nutrition/Satinballs/satinballs2.html

How old is your dog? Most dogs go thru the scrawney stage where they look gangley & skinny especially when going thru growth stages. They grow in height or length & the body weight redistributes.

I never really was able to put much weight on my male until he was almost 3 yrs old. He always looked like a skinny cayote no matter how much I fed him. He is extremely active & just metabolizes food like crazy. I got so that I was more concerned with keeping on the weight that he had & not loosing any, then I was with putting more on him. I would just add some extra snacks/treats here & there (usually around bedtime so he didn't have the chance to run the calories off) or just drop a little tiny bit of extra meat in his meals here & there. If I tried to feed bigger meals, he would get loose stool. (I feed all raw) If I added an extra meal that would screw up our exercise/traiing schedule, as I am very careful about exercising too soon after or before meals because of the increased risks of bloat in GSDs.

You might try adding another small meal during the day or at bedtime or feeding more of the Buffalo Blue & less of the Chicken Soup formula.
I didn't have any issues with him having a thin coat, though.

In the Chicken soup brand large breed puppy
The calcium/phosporus ratio is 1.2 to 1.0 which is pretty close to optimal I thought.

You are right I chose to go with a bag of it because it had a higher fat and protein ration as well as more calories per serving.

The Blue buffalo wilderness has 42% protein, and a calcium phosporous ratio of 1.0 to .9
Since they both seem to tolerate the blue buffalo well I might end up switching to only that for a while. I had problems with EVO causing upset stomachs and Yote turned his nose up at Core after a while.

One thing I have learned while studying canine nutrition is how well healthy dogs use fat.

By "fat," I don't mean cooked fat. Since I don't know if I would want to add raw animal fat (since it is connected to raw meat and I don't like kibble/raw combined), I'd probably consider a very gradual addition of top-quality cold-pressed oil.

I buy the best oils (nothing that I see in a regular supermarket) and treat them carefully. I'd feel good adding cold-pressed olive, grapeseed, canola, or hemp oil. (This is in addition to, never in place of, the daily fish oil for long-chain Omega 3s.)

Only fats/oils have twice the calories of protein or carbs.

Remember that Vitamin E is also given when we give oil.

Again, I don't mean cooked fat. The properties of fat are changed when they are cooked (or become rancid). (For example, "holiday pancreatitis" is acute pancreatitis usually triggered by a sudden increase of cooked fats (gravy, cooked roasts, etc.).

And of course nothing here applies to any dog with a chronic ailment such as chronic pancreatitis. I'm talking about healthy adult dogs.

All strictly MHO, and I am not a health professional.

He is healthy!
He gets Fish oil and E everyday.
Right now he eats at around 7am, 3 pm and 8 pm.

I do have cold pressed hemp oil, I never thought to add it to his diet though. I also have cold pressed grape seed and almond, coconut oil, safflower and olive.

I have used Satin balls in the past when Nico was competing and they were great, but she was eating raw so I wasn't concerned with the digestion rates.

I am considering dropping one meal of dry and replacing with either THK or canned and adding some fat to it. Maybe the evening meal so that it has lots of time to digest.

For years I fed my x-counrty horse 1/2 cup of corn oil with each of his grain feedings to keep weight on him without adding extra grain. I know that dogs use fat like we use carbs, but I would never have thought about feeding additional oils to my dog. Obviously, not corn oil, but other oils. I always fed the Grizley Salmon oil. If feeding the additional oils do they need any additional suppliments for processing like the Vit E with the salmnon oil? Just curious.

Also after 6 months the pups should not be on a large breed pup food anyway as it promotes more rapid growth then is good for the joints.

When adding extra oil to his food what amount would I start with and what amount would I want to end up with.

I was thinking a teaspoon to start, but I have no idea how much I would want to gradually build up to.

I am also looking at canned food right now and not sure how to read the labels. The protein levels seem really low but I assume that is because the moisture level is so high.

I have fed the Wellness 95% cans in the past as a treat but I'm not sure if they are a good choice for this situation.

Good to give E with any oil supplement -- not at all just for fish oil.

Yes, the moisture is throwing you off. To compare moist and dry foods you have to do a dry matter conversion.

http://www.peteducation.com/article.cfm?c=2+1770&aid=668

About your oil plan: I would start with a teaspoon, too. That would be 42+ calories right there, for each meal you added it to. An extra 85 calories a day, depending on the size of the dog, could be meaningful. How much does the dog weigh? That would be needed to estimate the RER, or Resting Energy Requirement, in calories, which could then be used when figuring what part of the diet a particular amount of added fat would be.