One of the best ways to put weight on a dog is with something called "satin balls". You can find the recipe on many sites on the internet. Some people use it to put weight on their dogs before dog shows, but it's especially good for emaciated dogs and dogs who won't eat. It's high in fat so it puts on weight quickly, but it's also got other ingredients to make it a total diet so it can be fed alone or as a supplement.
My puppy hasn't been eating much and underneath all her fuzz she's skin and bones so I decided to mix up a batch to bring her up to a healthy weight
Step 1: Gather Indgredients
This is the original recipe:
10 pounds hamburger meat (the cheapest kind)
1 lg. box of Total cereal
1 lg. box oatmeal
1 jar of wheat germ
1 1/4 cup veg oil
1 1/4 cup of unsulphured molasses
10 raw eggs AND shells
10 envelopes of unflavored gelatin
pinch of salt
However, if you just want to try them out or have a small dog, I recipe this scaled down version (1/10th or the original).
1 pound cheap hamburger (for high fat %)
1 1/3 cups Total cereal
1 1/2 cups uncooked oatmeal
1 raw egg
6 tablespoons wheat germ
1 package Knox unflavored gelatin
2 tablespoons oil
2 tablespoons unsulphured molasses
Pinch of salt
The only thing I suggest you change is the oil; vegtable oil has no health benefit, so substitute it with an oil that does (like flax seed oil which is high in healthy omega 3s).
Step 2: Mix the Ingredients
Mix everything together in a big bowl. I recommend putting the dry ingredients first, then the oils, then the egg, then the meat. That way you don't have to wash your hands in between ingredients
Step 3: Form Patties
You can form them into balls like the name suggests. I prefer patties though because they are easier to stack in the freezer that way.
How much you put in each serving really depends on your individual dog... I made 14 patties out of the smaller portion recipe
Step 4: Freeze
Put the patties into bags and freeze them. Since they are served raw you need to thaw them individually when you are ready to serve them.
Step 5: Serve
Your dog will LOVE these, and you should see weight gain relatively shortly.
The only downside is that it's raw. I know that many people serve raw and I support that, but I can't but help but be paranoid about bacteria contamination. Particularly cause she takes extra special treats to her crate. So I wipe down the floor and her crate between feedings, and wash her bowl each day