GSPs are notorious for their fast metabolism under any circumstances, but additional demands from increased activity, cold temperatures, growth, whelping/nursing, stress, recovery from illness or injury, etc. can make weight maintenance even more difficult. The following is a collection of tips I have gathered from personal experience and from other working/sled dog people.

Before even getting into this, please be sure your GSP really needs to gain weight. It is normal for this breed to have fairly prominent hip bones and to show the back 1-3 ribs at rest.

Management: GSPs need a warm place to snooze whether they are in a kennel or in the house, as keeping warm burns substantial calories by itself. Outdoor houses can be packed with straw that the dog can burrow into, which unlike fabric doesn’t harm the dog if it’s eaten. Insulated houses with doors are useful for very cold climates. If dogs get along well they can stay warmer curling up in a house with a buddy. Dog jackets are available but should only be left on unattended dogs that won’t shred-and-eat.
Having said all that… if an outdoor GSP is loosing weight, you may be fighting a loosing battle until it’s boxed/crated in a heated area at night.

Feeding schedule: Dogs needing large quantities of food should be fed more than once a day so they can better accommodate the volume of feed required. An old farmer’s trick is to feed the larger meal in the evening before the animal settles down for the night, as their metabolism will slow down a bit and they will get a little more out of the feed consumed.

Hydration: Dogs with increased caloric demands will probably need more water than normal, especially if they’re working hard in hot weather or nursing. In addition to fresh, clean water, water flavored with a bit of food- aka ‘baited’ water- can help. I give my dogs 1c of food in 4c of warm water every morning in addition to fresh, clean water available in their kennels and/or baited water as needed with additional athletic activities or when the water buckets are frozen solid.
Adding water to food and/or soaking food is more controversial since nutrients and probiotics can wash or cook out of food left with water too hot or left in too long. Watering the main meal down too much can also cause the food to just shoot out the other end of the dog- which doesn’t do us much good! Current recommendations are to add up to 1c of lukewarm water to 2-3c kibble and immediately serve.

Kibble: If your GSP is a hard keeper, s/he should be on a 30% protein/20% fat or better kibble to start with. Trying to keep up with their calorie demands using anything less that that will most likely become futile since most average sized dogs have a tough time digesting more than a pound of kibble a day. Premium kibble is usually around 4oz/cup, so at more than 4c/day you may notice the dog getting the runs without progress on weight maintenance (in fact you could be going backwards!).
There are a few ultra-premium foods designed for distance mushers that are even more concentrated, although normally these wouldn’t be required unless a GSP is working very hard in cold weather. Examples (NOT a complete list): Blackwood 7000 (34%/25%), Eagle Ultra (? being revamped as of Dec ‘08), Dr Tim’s Momentum (37%/23%), and Red Paw 38 (38%/25%).

Supplementing: If a GSP is still struggling to maintain weight after all the previous tricks are implemented, it may be time to add even more ‘omph’ to their diet. Any supplements should target adding more protein and fat, as additional carbohydrates do not provide sufficient calorie density and can result in digestive upset in a dog already consuming a high volume of food.
High fat supplements should be added GRADUALLY to prevent the dog from getting sick! Ideally periods of high nutritional demand (hunting season, cold weather, etc) should be anticipated, and such supplements worked into a GSPs regular diet at least a month ahead of time.
Meat is the most readily available high calorie supplement. Poultry is more easily digested, although beef and lamb are both also used with success (especially in colder weather). Raw meat is said to have higher nutritional value but cooked meat is certainly better than none. Cooked bones of any type should be avoided to prevent injuries from splinters. I usually start feeding 3-4oz every other day for 7-10 days, then 3-4oz every day for another 7-10 days. At that point I can usually add more meat as needed without worrying about digestive upset.
A rule of thumb I have seen is that kibble-based diets can be supplemented with up to a half pound of meat per day without unbalancing overall vitamins and minerals. There are also nutritionally balanced ground meat mixtures locally available for greyhounds, mushers, mink farmers, etc. but finding them usually requires some foot work. Example: Champaine race diet- a blend of liver, chicken, beef, eggs, wheat germ oil, bone meal, etc- is mixed in Washington state and shipped around north America and Alaska.
Raw eggs have been controversial due to biotin binding, but the consensus I’ve seen indicates 3-4 per week is probably OK. If you’re worried, your GSP will still be glad to eat them cooked any number of ways.
For those times a freezer isn’t available, canned or freeze dried meat can help. Another handy supplement is Annamaet Impact, which is a high protien/ high fat/ high calorie powder that can be mixed with water and added to kibble.

I’ve had to feed my GSP crew up to 1lb (4c) of kibble and 1lb of Champaine race diet per day while doing 10+ mile skijoring runs in temperatures down in the teens just to keep them from loosing weight, and they were spending most of the rest of the day and all night sleeping in the house. The good news is that this is probably the most extreme case GSP owners will run into.

This is a really nice summary Meg. A couple questions I'd like the musher's opinion on - as your group really delves into nutritional science:

I don't have terrible issues with maintaining weight, but we free feed and it works for us at home.However, when you free feed, food is NOT a priority and my dogs could take it or leave it most of the time. So when we travel to a field trial or go wild bird hunting, they really aren't terribly interested in eating much. This is the worst time for them not to eat, so then I have to resort to doping their food. I'm sure most dogs would be thrilled to have any of the below items added to their food, but mine still are only moderately impressed. Here are the things I've used in desperation, trying to get them to eat:

Cooked meat and eggs (raw just scares me, I don't need a hunting or trial dog getting the runs) - as for the meat, I've used chicken, beef, wild game (elk and deer) and salmon

Plain yogurt

High fat (4% I think it is) cottage cheese

Homemade or canned chicken or beef broth

Canned tuna

Canned chicken

In desperation, I even used canned cat food once. They loved that, but no one could stand to be around them in the camper

Keep in mind this is for usually no more than 2 days at a normal field trial, but could be up to a week for wild hunting or nationals.

Anything there concern you?

Jean

Jean: Cooked meat is still good stuff, and you definately want to cook game and salmon since both can contain nasty parasites.

You've actually hit on why mushers usually don't free feed. Sled dog pups are often bred with 'good eaters' in mind and are typically trained to hit the bowl on cue from weaning to grave. Since they're on trucks a lot and distance dogs only have brief resting periods during training and racing, they just need to get on the chow when it's made available.

Unfortunately I don't have a better answer to getting them to eat on command other than what you're already doing. Canned cat food is an old water/food baiting trick BTW. I've heard of tins of sardines and vienna sausages as well.

Thanks Meg. Makes me feel better that you didn't say "Oh god you fed them WHAT?!"

Sheesh, sardine breath would be totally intolerable.

And I'm not surprised mushers don't free feed for that reason. There are both positives and negatives to it for sure. For us, we decided that it was more important to have zero fights over food, which is why we do it.

Jean

Tessa- I've got to head out to lunch, but I'll leave you with this ISDRA link to back up my basic outline for now:
http://www.isdra.org/Home_pg/Contents/Feeding.asp

There has just been something of a breakthrough in the scientific understanding of the physiology of sled dog performance, particularly with Iditarod/Quest 'extreme' distance racing teams. I'll try to find some links for you when I come back, but suffice to say they've discovered more evidence to support that canines are metabolically capable of things humans just aren't. How dogs can turn fat into energy is one part of their findings.

OK, here's the information I was after:

http://www.adn.com/iditarod/2008/story/404261.html
http://www.nytimes.com/2008/05/06/science/06dogs.html?_r=1&ex=1210737600&en=313979157c777587&ei=5070&emc=eta1

Interesting stuff.

Re oatmeal: It's good stuff for man and beast IMO, with some interesting cardiovascular benefits. I like to see it in dog food. Heck, I like to see it in my bowl in the morning, with lots of raisins and cinnamon....mmm...
However, there are only 4 cals/gram in carbs as opposed to over 9cals/gram in fat, which means we're only getting so much extra energy for the grams we're squeezing into the dog. Oats also have a lot of fiber- which for us is good, but for a dog already pushed to maximum gut capacity it can cause the digestive tract to go into offload-mode.

When trying to put weight on a run-down dog we're always riding the edge of feeding too much and having the dog blow everything out the other end as diarreah. In fact, if you have a skinny dog with no discernable health issues and chronic runs on a good diet, the FIRST thing to try is backing off the volume of food and seeing if that helps. It's totally counter-intuative but not uncommon.

The reason I cut off at about 4c of kibble is because Joe Runyan had been doing some feed studies years ago with his sled dog kennel, and they all noticed that over about  a pound it started being a loosing proposition. This was all carefully, scientifically documented, and they were able to play with pretty high zoot rations. People have noticed similar results anicdotally since then.

Kibble has evolved since then but it's a reasonable rule of thumb IMO.