As I search the web for info about cat nutrition, I find there is a lot of confusion about by-products. Many canned food contains meat by-products, and many dry foods contain meat by-product meal. What is this stuff?
According to the Association of American Feed Control Officials (AAFCO): Meat By-Products - the non rendered, clean parts, other than meat, derived from slaughtered mammals. It includes, but is not limited to, lungs, spleen, kidneys, brain, livers, blood, bone, partially defatted low-temperature fatty tissue and stomachs and intestines freed of their contents. It does not include hair, horns, teeth and hooves.
If you think about what a cat eats in the wild, mouse by-products make sense. The cat will eat the whole mouse, including the liver, heart, blood, bones and everything. But by-products can also be feathers, feet, or anything that is considered un-fit for human consumption. Some have claimed that diseased organs can be included in the mix. There is no way to tell from the label what is included in the by-products. And if it says "meat by-product", you don't even know the species.
Meal is made by grinding and rendering (cooking for a long time at a high temperature to remove fat and moisture) the meat or by-product. It is more commonly used in dry food.
I choose not to feed my cats by-products. Both the canned and dry foods I have chosen, however, do contain specific meat meals. Unless you feed your cats raw food, I think it would be very hard to avoid the meals.