Initially, certain meat by-products are allowed to be part of the recipe for kitten food as it is also a good source of protein. Examples of meat by-products include the chicken spleen, liver, intestines cleaned of their contents, etc.
While conventional wisdom says that meat by-products are inferior, the new perspective is that these ingredients are safe. In addition, proponents claim that including meat by-products in pet food is ecologically sound because it reduces food waste.