In fact, there are entire food chains based on feces. Large animals, or those that consume a highly nutritious diet, often are not very efficient in extracting all the nutritional content of food. There is often plenty of food value in feces, which also concentrate it in a form that smaller or more efficient animals can use.
Rabbits eat their own shit, in order to maximize nutrient extraction from what they otherwise eat. Presumably they crap in one spot for the reserve feces and another for the used up stuff.
Right. And what one ingests must surely have a relation with the amount of calories left over. Are there foods or ingredients that make your poo hipocaloric or hypercaloric? There must be something about that, but I cannot find it. Just noticing that the animal dung burnt is mostly from herbivores, often cows, but that may be because they are easier to keep than tigers. Does pig manure get burnt often? No idea.
Man, this thread had left me pooped! 
My Dr years ago did a stint in the peace corps and one of the things he did was study the poop of africans still living in tribal communities eating mostly traditional primitive diets. He told me that the average size poop of these natives was 4 1/2#. That is like 2 quarts, hard to imagine. He said that none of them were fat but could hold ungodly amounts of food which was 90% fibrous vegetable matter low in fats and proteins. He claims that they had evolved around this diet and were extremely healthy.