By Products in Pet Food

As with our own diets, pet owners are faced with diverse and often conflicting opinions about pet food.   It can often be challenging to wade through the varying choices and marketing strategies to find valid, unbiased information to make an informed decision.  There are too many aspects of pet nutrition to tackle in one blog, so I would like to discuss a current hot topic – by-products and meals in pet foods.  Recently, there has been a lot of discussion regarding the use of by-products in pet foods and unfortunately, this has created some misconceptions and aversions.

In order to understand how by-products and meals are used in pet foods, it is important to understand the terminology used in the slaughter process.  The Association of American Feed Control Officials (AAFCO) is an advisory body of state and federal regulators that develops nutrient standards and ingredient definitions for animals, whether livestock or pets.  The following definitions are taken from the AAFCO publications.


Meat is defined as “primarily the muscle tissue of the animal…this may include less appealing cuts of meat, including the heart muscle, and the muscle that separates the heart and lungs from the rest of the internal organs.  Meat for pet food is mechanically separated from the bone resulting in finely ground product with a paste-like consistency (similar to what is used in hot dogs).”

Rendered products are products “that have been subjected to cooking to destroy any harmful bacteria before they are shipped to a pet food manufacturing plant…materials are subject to heat and pressure, removing most of the water and fat and leaving primarily protein and minerals.”

Meat By-products is “non-rendered, clean parts, other than meat, derived from slaughtered mammals.  It includes, but is not limited to, lungs, spleen, kidneys, brain, liver, blood, bone, partially defatted low temperature fatty tissue, stomach or intestine freed of their contents.  It does not include hair, horns, teeth, and hoofs.”

Meat Meal “is the rendered product from mammal tissues, exclusive of any added blood, hair, hoof, horn, hide trimmings, manure, stomach and rumen contents.”  The rendered material is then ground to form uniform sized particles.  Meat and Bone Meal includes bone.  Animal By-product Meal is made from meat by-products and will sometimes contain an entire carcass.

Materials classified as by-products in pet foods are those that are less frequently consumed in the North American human food industry.  However, in many cultures and high end restaurants these products are often considered delicacies, such as organ meats (liver, heart, tongue), Scottish haggis is made with intestine, sweet breads is made from pancreas, blood or black pudding is made with blood.  Human sausages, cold cuts, and chicken wings that are regularly consumed all fit the definition of a meat by-product.    Many pet food marketing strategies create the impression that by-products are the inedible leftovers being used as sub-standard ingredients in commercial pet foods, when in reality by-products are often the more nutritious parts of the slaughtered animal.  Different organs provide different nutrients – bone is high in calcium, liver is high in vitamins, cardiac tissue contains amino acids taurine and L-carnitine.  Consider how an animal hunts and eats.  After killing, a carnivore will eat the internal organs first, they know that this is where they get the most nutrients.  The muscle is often consumed later.

When I spent some time reviewing the ingredients of many pet foods that market their food as being “human-grade” or by-product free, I was surprised at the number of foods that list chicken liver, chicken fat, chicken meal, chicken giblets (liver, heart, kidney), beef liver, lamb liver and numerous types of meal products.  Many of these companies have avoided the word “by-product” by listing the exact organ meat used but their product contains organs that are classified as by-products under the AAFCO guidelines.

Beyond the nutritional value in organs classified as by-products, it is important to consider the wastage that occurs when only muscle meat is consumed.  There is significant environmental impact of raising increasing numbers of livestock to meet human consumption demands.  Parts of slaughtered animals that are not consumed have to be disposed of via decomposition or incineration which also have an environmental impact.  The whole animal or “nose-to-tail” movement has been gaining popularity and is focused on environmental stewardship, ethical consumption of meat and the sustainability of the farming industry.   The inclusion of by-products in pet food allows for ethical use of livestock while providing the quality nutrition pet owners are striving for.



By Tiffany Renwick, DVM