Protein Sources for Poultry Diets
The two major nutrients used in formulating poultry diets are energy and protein. The need for protein includes requirements for specific amino acids that are the building blocks of the protein. There are a variety of different protein sources that are suitable for use in poultry diets. They all differ in their amino acid profile. When feeding corn, soybean meal is typically used because their amino acid profiles complement each other. When using other dietary energy sources, alternative feed ingredients may play a more important role.
Soy-free poultry diets (Oregon State University)