The Truth is in the Label!
Here are labels from two major brands of dog food.
For this Fromm diet note that chicken is listed first (that is by wet weight) and the largest ingredient in the diet is chicken meal. By definition chicken meal is made of only chicken muscle tissue.
Brown rice is the 1st and most used ingredient in this Royal Canin product. Chicken by-product meal is the second most used ingredient in this diet. Chicken by-product meal is the waste material left over after the parts fit for human consumption are removed which then could include necks, feet, undeveloped eggs and intestines, exclusive of feathers, except in such amounts as might occur unavoidable in good processing practice.
Royal Canin is a product of Mars Petcare.