While they are a nutritious food and contain good quality animal protein, eggs are
not high in protein. They are about 12% which is much lower than any chicken feed.
If adding cat food, check the protein content on the guaranteed analysis. Some cheap canned cat food is lower in protein than chicken feed.
Soybeans are high in protein but soybean oil contains
zero protein. The protein is in the meal from whence the oil is extracted. Hence the word oil, which means it is a fat, not a protein. There is little nutritional value other than as a fat.
http://nutritiondata.self.com/facts/fats-and-oils/507/2
If one is going to increase protein, one needs to know the actual crude protein percentage of what they're supplementing, otherwise it is a guess.
Amino acid profile of the supplement is just as important. It doesn't help to add something that may be high in crude protein but missing several of the essential amino acids. A high crude protein food that is deficient in one or more amino acids can still cause protein malnutrition. The high crude protein may be in the form of non-essential amino acids or essential ones already in good supply and the result is excretion of those excesses as nitrogenous waste when the amino acid profile of the food isn't matched to nutritional needs of the animal. Poultry feeds made from vegetative sources need to supplement synthetic lysine, methionine and sometimes tryptophan to meet the nutritional requirements.
Check the 'limiting amino acid concept' discussion in the next link.
http://feed-additives.evonik.com/pr...nutrition/animal-nutrition/Pages/default.aspx
For egg layers, it's best to avoid giving too much fish as that will flavor the eggs. It is an excellent source of animal protein though. I use canned mackerel since it is about 1/4 the price of tuna.
Egg eating isn't necessarily a protein craving. It usually starts with a broken egg, then one or more hens taste the contents, discover how good they taste and may then continue to break them for the treat inside.