Lamb by-products are the non-rendered, clean parts, other than meat, derived from slaughtered lamb. 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 hoofs. Use of this ingredient from mammalian origins is restricted to non-ruminant (cud chewing) feeds. (AAFCO, 2003)
Meat by-products are not meat and can include almost any part of the animal other than meat, they are cheap ingredients and are not advisable to feed our pets.