Cat Food Uncovered

In countries where the pet food industry is poorly regulated, diseased animals and spoiled unsold meat end up in cat food. The British pet food industry uses by-products (the bits we don’t like to think about) from animals passed fit for human consumption and BSE-contaminated tissue was removed from pet food long before it was removed from most human food.

In some places, ground-up cats and dogs can end up in pet food. Sanimal of Quebec, Canada mostly process pig and chicken, but rendered approx 18,200 kg of cat and dog flesh each week. The resulting protein meal is sold to pet food manufacturers and animal feed companies. A spokesperson said that the food was healthy and good and suggested that people were squeamish about "cannibal" pet food. However the firm will no longer render domestic animal carcasses, even though this is an efficient, environmentally-friendly way to dispose of carcasses from animal shelters or road kill.

Are we just squeamish about recycling pets into pet food? Bodies must be disposed of and rendering is less polluting than cremation or burial. Sheep and cattle carcasses were burnt and buried en masse during the UK’s foot and mouth epidemic – they could not be safely rendered. The air was full of acrid smoke, charred scraps floated from pyres; fluids leaked from burial pits – these disposal methods caused pollution. The question is not "should cats and dogs be rendered" but "should the rendered product be fed back to cats and dogs".

Britain was plagued with Bovine Spongiform Encephalopathy (BSE, Mad Cow Disease) due to feeding sheep and cow proteins to cattle. The causative agent (a prion) survived rendering. In humans, new variant Creutzfeld-Jacob Disease (vCJD) is linked to eating BSE-infected beef. FSE, the feline version, was linked to cat food or infected meat scraps. Apart from the aesthetics of "cannibal" cat food, there may be genuine health concerns about feeding animals back to members of their own species. I decided to look at what is in pet food and how it is manufactured. I originally studied this topic for a University term paper and grossed out the lecturer!

Where Does Cat Food Come From? – The Rendering Process

Most pet food comes from multinational companies which also own human food concerns. This allows them to profitably use waste products from the human food chain. Many pet food manufacturers use good quality ingredients, others do not. Unless they own and control their own rendering plants, they are dependent on the quality controls and integrity of rendering facilities.

The raw materials e.g. carcasses are rendered. This is the process of processing raw animal material on an industrial scale to remove moisture and fat (note: some rendering plants produce a meat slurry rather than a dry product). Some rendering plants are linked to a particular kind of slaughterhouse; e.g. those near poultry processing plants may deal exclusively with poultry by-products, some specialize in fish products.

In the USA, independent renderers process raw material from small packing houses, supermarkets, etc; packer renderers process raw material from only the species they are slaughtering, poultry processors process poultry by-products while protein blenders purchase and dry rendered tankage from the preceding processors as a the raw material for their own process.

The raw product is blended in order to maintain a certain ratio between the contents e.g. animal carcasses and supermarket rejects. The carcasses are loaded into a stainless-steel pit or hopper and an auger-grinder at the bottom grinds up the ingredients into small pieces. It is a larger version of the old table-clamped meat grinder used in the days before food processors. The pieces are taken to another grinder for fine shredding.

The shredded material is cooked at 280 Fahrenheit for 60 minutes (US figures, those in Britain and Europe may differ). Meat melts off of bones to produce a soup or slurry. Yellow greasy fat or tallow rises to the top and is skimmed off. Some pet food manufacturers use this slurry. Otherwise, the cooked meat and bone go to a press, which squeezes out the remaining moisture and pulverizes the product into a gritty powder. The grit is sifted to remove excess hair and large bone chips. The end products are yellow grease, meat and bone meal.

Meat – prime steak, juicy liver, succulent turkey etc – are the primary products of the food industry and the ones which end up on the human dinner table. A by-product is literally any secondary or incidental product produced in the course of making a primary food ingredient, not just the internal organs. For example feathers are a poultry by-product, hair is a meat (or animal) by-product. These items are removed from the carcass and hydrolyzed (pressure cooked with steam until they form an edible gel). This turns feathers or hair into an acceptable pet food ingredient shown on labels as "poultry by-products."

The term "meal" on a cat food label means that the material in the meal have been rendered. The quality and content of the meal may be variable across batches. In the USA, this means that some some question the nutritional value of the by-products. James Morris and Quinton Rogers, two professors with the Department of Molecular Biosciences, University of California at Davis Veterinary School of Medicine, felt there was a lack of information on the bioavailability of nutrients of pet food ingredients. The pet food labels give the supposed nutritional adequacy, but the nutrients are no good if they are in a form indigestible by the pet. Pet food labeling is described later.

Depending on the contents (grade), rendered material is sold to pet food manufacturers, farm livestock feed manufacturers and as honestly named fertilizers such as blood meal, bone-meal, "blood and bone" and "hoof and horn".

Where Do The Ingredients Come From?

The animals rendered come from various sources. In the US, they are know as 4D animals: Dead, Diseased, Dying or Disabled. Some died or are dying from unknown causes and will have been treated with various drugs, possibly including a euthanizing drug. The animals are delivered to a "receiving plant" where the hide (sold to a tannery) skin, fats and meat are removed. The meat from these animals can be sold for pet food after it is completely covered in charcoal (to prevent ingestion by humans), and marked "unfit for human consumption". If the 4D animals are already decomposing, they go straight for rendering.

In some countries, road kill which is too large to be buried along the roadside is sent for rendering. This is an efficient method of disposal. Condemned material from slaughterhouses goes for rendering: animals that died in transit, diseased animals or animal parts, blood, hair, feet, head and any part of the animal unsuitable for human consumption. Many of the "unspeakable parts" such as udders, lips, eyes etc end up in human processed meat products such as meat pies or sausages. Before the condemned material leaves the slaughterhouse it is "denatured" (doused with chemicals) to prevent it from getting back into the human food chain when transported to the rendering facilities. In Canada, the denaturing chemical is Birkolene B and its composition remains secret. In the U.S. carbolic acid (potentially corrosive disinfectant, toxic), creosote (used for wood-preservation or as a disinfectant, toxic), fuel oil, kerosene and citronella (an insect repellent made from lemon grass) may be used. In other countries, the meat is simply dyed e.g. blue or green using a non-toxic dye.

James Morris, a professor at the School of Veterinary Medicine at Davis, California, stated that any products not fit for human consumption were very well sterilized so that nothing can be transmitted to the animal. Many believe this to be a na?ve statement especially after the British BSE situation. In the UK, cattle feed was believed to be well sterilized until BSE emerged; the causal agent was not destroyed at the sterilizing temperature.

About 50% of a food-producing animal is not used in human food. This includes bones, blood, intestines, many internal organs, ligaments, hooves and rind. These "by-products" of the human food industry are used in animal feeds and fertilizer. The by-products are not necessarily unhealthy or inedible, parts of the animal that we would rather not think about end up in processed meat or sausages. The pet food market benefits pet owners (convenience, ready-made balanced diet) and also benefits human food industries and animal farmers by providing a market for by-products. It is not a new trade. In Britain half a century ago, ill or old livestock ended up at the knackers (small scale slaughterhouse) and often ended up being fed to hounds or farm dogs. Many towns had a "cat’s meat man" who sold skewers of waste meat to cat owners for a couple of pennies.

Pet Food Regulatory Bodies

The UK Pet Food Manufacturers Association (PFMA) states that it uses those parts of the carcass which are either surplus to human requirements or which are not normally consumed by people in the UK. Companies which are members of the PFMA operate their own quality assurance policies including strict specifications for material supplies, routine testing of all incoming materials and the use of vendor assurance schemes (and audits) to monitor their suppliers. The British pet food industry also uses sources of meat and meal from the UK, USA Canada, Australasia and various European countries. All materials imported must comply with the strict British legislation.

Britain pet food manufacturers only use materials from animals which are generally accepted in the human food chain. They do not use equine (a peculiarly British taboo), whales or other sea mammals, kangaroos or a number of other species not eaten by humans. It does use beef, lamb, poultry, pork, fish, shellfish, rabbit and game. The PFMA’s policies are often ahead of UK legislation, for example when BSE appeared, the PFMA banned "high risk" cattle parts from pet food long before those parts were banned from human food.

The PFMA practice of only using materials derived from animals passed as fit for human consumption is now incorporated into the Animal By-Products Order and PFMA member companies using animal material derived from the UK are recommended to only buy from and sell to companies registered under the Animal By-Products Order. There are also regulations governing labeling of pet food. Pet food labeling is described later.

In the US and Canada, the pet food industry is virtually self-regulated. In the U.S., the Association of American Feed Control Officials (AAFCO) sets guidelines and definitions for animal feed, including pet foods. In Canada, there are virtually no regulations in this industry. The "Labeling Act" states that the label must contain the name and address of the manufacturer, the weight of the product, and if it is made for a dog or cat. The Canadian Veterinary Medical Association (CVMA) and the (Pet Food Association of Canada (PFAC) are voluntary organizations and relying on the integrity of the company which they certify, stating that the ingredients are not below minimum standards. 85%-90% of pet food sold in Canada is of US origin and neither the CVMA or PFAC have any control over the ingredients used in these foods.

The Pet Food Industry Association of Australia (PFIAA) has adopted many of the AAFCO conventions in labeling and regulating the pet food industry. I have no information about pet food regulatory bodies in other countries.

Pet Food Labeling

Most countries have food labeling regulations. Pet-food manufactured in the USA must be manufactured in accordance with FDA and USDA regulations. It must state the source species on the label e.g. "chicken by-products" "horsemeat and horsemeat by-products" unless the meat and meat by-product are derived unless the meat and meat by-products are from cattle, swine, sheep and goats. Diseased tissue may not be used in pet-food. However, at a rendering plant where animals are processed en masse, the label of a particular "run" of product is defined by the predominance of a specific animal. Something labeled "pig by-product" may not be exclusively pig in origin, just mostly pig. It is sold to pet-food manufacturers as "pig by-products" which is what goes on the can label. Often, only major ingredients are listed by type. In Britain many "economy" or "budget" pet-foods simply state "meat and meat derivatives". In most countries, there is no requirement to name the source species of the ingredient "animal fat".

In the USA, AAFCO does not permit "all" or "100%" to be used on any product containing several ingredients (necessary additives such as water, preservatives or "condiments" are not considered to be "ingredients") . All-meat diets are not nutritionally balanced, but due to consumer demand some manufacturers produce 95% and 100% canned meats. These are supplemental or complementary foods and the label must state this. AAFCO states that cat foods labeled "dinner" contains at least 25% (by weight) of the named meat/fish and must have a description which implies that other ingredients are present (e.g. a descriptor such as recipe, platter, entr?e (excluding water) do not have to be listed.

"With" e.g. "With beef" indicates that the named ingredient constitutes at least 3% of the food by weight (excluding water). AAFCO has not defined the term "all-natural." To some consumers this means using natural preservatives like Vitamin E or Vitamin C in place of artificial preservatives such as lieu of BHA, BHT or ethoxquin, but to others it means the food contains no artificial ingredients at all.

The Pet Food Industry Association of Australia (PFIAA) has developed a code of practice which provides detailed guidelines to manufacturers for pet food labeling. Pet food labeling in Australia is governed by both state industry laws and consumer product laws In some states of Australia, there is a legal requirement that the words "PET FOOD ONLY" appear on the label (or lid of canned products) of pet food products made in that state. To further assist consumers to identify the product as pet food, some state legislation makes it mandatory for a picture of the animal species for which it is intended (e.g. a dog or cat) to feature on the label. A minimum guaranteed analysis declaration is also required stating minimum percentage crude protein, crude fat, crude fibre, moisture, salt (NaCl) and, optionally, other ingredients. The product can only be described as "all meat" or "100% meat" when composed wholly of the named ingredient or by-products of this ingredient (excepting water or preservatives). PFIAA has adopted many of the AAFCO conventions.

In the USA, cat foods must be "complete" and "balanced" if they are to be fed as the sole diet. In the UK, the term "complete" distinguishes a balanced diet food from "complementary" (treat) food. If the product does not contain complete and balanced nutrition, the label should state "not to be fed as a sole diet," "for intermittent feeding only" or words of similar meaning. Snacks/treats do not require nutritional adequacy statements.

British pet food labels must state whether the product is complete or complementary; the species for which the product is intended; directions for use and a typical analysis i.e. the percentage of the following must be listed: proteins, oils & fats, fiber in the product, moisture in the product when it exceeds14%, ash in the product (ash represents the mineral content of the food and is determined chemically by the burning of the product). The ingredients must be listed in descending order by weight using either category names or individual names. Mixing category names and individual names on a label is only allowed if an individual ingredient does not fall into any of the prescribed categories.

Regulated category names include ‘meat and animal derivatives’, ‘cereals’, ‘derivatives of vegetable origin’. If particular attention is drawn to a specific ingredient (eg With Chicken), the percentage of that ingredient component must also be listed. If preservatives, antioxidants or colorants have been added to the product their presence has to be declared using category or chemical names. If Vitamins A D & E are added to the product, their presence and level has to be declared. The level must include both the quantity naturally present in the raw materials and the quantity added.

Price is often a good indicator of quality since low cost brands of cat food must contain low cost raw materials. Budget brands generally contain "meat and meat derivatives" and "cereal". In premium brands cereal appears in a smaller percentage or not at all. The texture of budget brands is more glutinous and less meat-like than the texture of gourmet brands and the smell is stronger.

American pet food nutritional standards are set by the National Research Council (NRC) of the Academy of Sciences. The standards were based on purified diets and required feeding trials for pet foods claimed to be "complete" and "balanced." The pet food industry found the feeding trials too restrictive and expensive, so AAFCO designed a procedure permitting nutritional claims based by chemically analyzing the food for compliance with "Nutrient Profiles." Chemical analysis addresses content, but not palatability, digestibility or biological availability of the nutrients. A cat food can therefore be labeled nutritionally complete even if the cat’s digestive system cannot extract those nutrients. AAFCO compensated by adding a "safety factor" so that foods contain more than the NRC recommended amount. In the UK, Waltham (Whiskas) also use an amount which compensates for possible losses. Overnutrition, however, is equally dangerous (e.g. hypervitaminosis).

How is Canned Food and Kibble Made?

The raw materials e.g. cattle carcasses are rendered. Pet food manufacturers buy either the meat slurry or the dried meal produced by rendering plants. Canned, dry or semi-moist cat food all contain similar ingredients. The ratio of protein, fat and fiber may be different and the amount of water present and the types of preservative used will differ greatly. Canned food is more bulky which is good for bowel action, but its soft texture means that teeth are not "exercised" which leads to tartar build-up and gum disease. Dry foods are convenient for the owner, but they are compact, energy dense and can cause constipation because the cat’s bowel does not get enough bulk to keep throughput smooth. The natural diet of the cat is semi-moist – moist muscle meat and tough skin and sinew.

Dry food is made with a machine called an expander or extruder. Raw materials are blended and the mixture is fed into an expander. It is then pressure cooked (steam, pressure, very high temperature) into a paste which is extruded through pipes which shapes blobs of paste into biscuits. These are puffed like popcorn and baked or dried, then sprayed with fat, digests and flavor enhancers. The cooking process kills bacteria, but may be ineffective against heat stable toxins or prions (causative agents in BSE). Non-extruded dry foods are baked and are denser and crunchier and may require no coating of fats of flavorings.

Most canned foods, especially budget varieties, are meat slurry which may or may not have been texturized and which contains a gelling agent to solidify them. A typical can of cat food may contain 45-50% meat or poultry by-products. Some contain more water than others – those in jelly or gravy containing the greatest amount of water. In order to compare different cans, the water has to be removed and an analysis performed on the remaining dry matter. Some labels provide a "dry matter analysis" to aid the comparison. To make canned food, the ground ingredients are mixed with additives. The meaty chunks are made using an extruder. The mixture is cooked and canned. The sealed cans are sterilized by pressure cooking. Some food is cooked in the can instead of beforehand.

Cooking, rendering, drying, canning and baking all destroy vitamins and other nutrients. The by-products used as raw ingredients are poorer quality and contain less nutritional value than the prime cuts of meat depicted on the label. Pet food manufacturers therefore fortify the product with vitamins and minerals.

The ‘Not-So-Hidden’ Ingredients

Some contaminants may survive the rendering, manufacture and cooking methods. Consequently cat food may also contain hormones (give to increase growth or milk yield), antibiotics (intensively reared animals are routinely medicated because disease spreads quickly in crowded conditions) or even the barbiturates sometimes used to humanely destroy the animal (electrocution or blunt trauma methods are more usual). Even less desirable contaminants also may enter the product.

To make kibble more appetizing, it is sprayed with fat mixed with flavor enhancers. The odor appeals to cats. Untreated kibble smells bland. Much of the fat used in pet food is rendered animal fat separated from the meat slurry, but it may also include rancid fats, fats and oils unsuitable for human use or grease from fast food restaurants. In America, restaurant grease is now a major component of the animal fat used in pet food. This reflects the American human diet. The used grease is stored in drums outdoors for long periods of time, giving it time to spoil. Fat processors or rendering companies blend it with different types of fat, stabilize it (e.g. with ethoxyquin, a substance not tested for safety in cats) and add antioxidants (slows spoilage). It is sold to various customers, including pet food manufacturers.

Cats are obligate carnivores and cannot digest vegetables, fruit or cereal. They rely on proteins and fats found in prey, not on vegetarian carbohydrates. Processed cereal and other vegetable proteins are cheap fillers. The items used include wheat, soy, maize, peanut hulls, rice and potato. The increase in vegetable protein is dramatically seen in dogs – the characteristic white dog turds of yesteryear are rarely found; they were caused by weathering of dog excrement rich in bone meal. Some cats do not cope well with cereal in their cat food. In Britain, some owners of Persian cats noted that a particular brand of kibble with a high cereal content caused vomiting and diarrhea in their cats.

The amount and type of carbohydrate in pet food affects the nutrient value the animal actually gets. White rice is highly digestible, even for cats, but other grains must be processed to make them 75%-80% digestible. Some cat foods advertise their vegetable ingredients so that it appeals to humans – cod with carrots, turkey and vegetables (green beans). Vegetable matter has poor nutritional value for cats and are best used as bulking agents for cats on weight reducing diets. Peanut hulls have no significant nutritional value and are only useful to increase dietary fiber – think about it, they are used in some bean bag toys!

Even wood ("cellulose", "cellulose pulp") can find its way into the mix – the blood-soaked sawdust on the slaughterhouse floor may be swept up with the offal and be rendered. Some meat by-products can legally contain blood soaked sawdust from the packing house floor. Dried Ruminant Waste may contain up to 35% sawdust and Undried Processed Animal Waste may contain up to 40% sawdust. There are health concerns about sawdust sweepings in cat food. Sawdust is a by-product from timber mills and the wood it comes from may have been chemically treated before the wood is sawn into planks. Many wood preservers are highly toxic, particularly to cats.

Take a look at the label – how many of the listed ingredients are vegetable products? How much of the kibble is dyed green to make it look like your cat is having a side order of peas with his beef? Often 2 out of the top 3 ingredients will be cereal or grain e.g. Ground Yellow Corn, Corn Gluten Meal or simply "cereal and vegetable derivatives". Cats are true carnivores; vegetables do not contain all the proteins they need (especially taurine, found only in meat). Some cats enjoy a few bits of vegetable or fruit for a change in taste, but the only reason cereal or soy to appears in commercial cat food is that these ingredients are cheaper than meat.

Even though the ingredients may state: "Beef, rice, cornmeal, beet pulp" in that order, the total amount of the 3 listed vegetable ingredients may be greater than the amount of the single listed meat ingredient! The following list (page 5) gives common pet food and meat industry labeling terms. I have tried to indicate which country the term applies to since food regulations, terms and definitions differ from country to country. The description indicates the type of content, but not the quality of the content.

Meat Based Ingredients

Animal by-products (US)
AAFCO define these as parts not used for human consumption e.g. kidney, lung and tripe. By-products are secondary or incidental products of the meat industry e.g. feathers, hair. Poultry by-products contains head, feet, underdeveloped eggs, intestines, feathers and blood. Fish by-products are fish process residues and can contain heads, tails, intestines and blood. Meat by-products can include hair, hooves, viscera and also the blood soaked sawdust.

Animal by-products (UK)
Unprocessed fresh or frozen slaughterhouse material. Processed material including blood meal, meat meal, meat and bone meal, greaves (the dry remnants left over after fat rendering)

Animal by-product meal (US)
Made by rendering those animal tissues which do not fall into the US categories listed here.

Animal digest (US)
Powder or liquid (soup, slurry) made from undecomposed animal tissue, broken down using chemical or enzymatic hydrolysis. The type of meat used is specified e.g. chicken, turkey, beef. Digests are ingredients not soluble in their natural state, but made soluble (hence useful as ingredients) with the use of heat, moisture and or chemicals/enzymes e.g. "Poultry Digest" may be processed chicken feet.

Fish meal (UK)
Dried processed whole fish and fish offal (e.g. cod heads).

Highly Pigmented Slurry (UK)
Mechanically Recovered Meat (UK) pulp. Contains varying amounts of bone. This slurry is reformatted into chunks and may be texturized.

Meal (US)
The ground or pulverized composite of animal feed-grade ingredients e.g. poultry by-product meal consists of the ground, rendered, clean parts of the carcass of slaughtered poultry, such as necks, feet, undeveloped eggs, and intestines, exclusive of feathers, except in such amounts as might occur unavoidably in good processing practices. Meal contains nothing humans would term meat.

Meat (US)
The clean flesh of slaughtered cattle, pigs, sheep or goats. Does include muscle meat, tongue, some organs, fat and skin of the animal. AAFCO define "meat" as the "clean flesh of slaughtered mammals as is limited to the striate muscle with or without the accompanying and overlying fat and the portions of the skin, sinew, nerve and blood vessels, which normally accompany the flesh."

Meat (UK)
The flesh, including fat, skin, rind, gristle and sinew in amounts naturally associated with the flesh used, of any animal or bird normally used for human consumption. Does include diaphragm, head meat (muscle meat and associated fatty tissue only), heart, kidney, liver, pancreas, tail meat, thymus and tongue. May (depending on intended use of product) include brains, feet, large and small intestines, lungs, esophagus, rectum, spinal cord, spleen, stomach, testicles, udder. (Meat Products and Spreadable Fish Products Regulations 1984)

Meat by-products (US)
The clean parts of slaughtered animals, excluding meat as defined above in "Meat (US)". Does include lungs, spleen, kidneys, brain, liver, blood, bone, fatty tissues, stomach and intestines. Does not include hooves, teeth, horns or hair.

Meat by-products (UK)
Offal e.g. liver, kidney, tripe, melts, lights. Also blood, bone, heads, feet, whole rabbit/chicken carcasses, other carcasses from which flesh has already been stripped for human consumption. Includes poultry by-products. (Waltham Book of Dog and Cat Nutrition)

Meat Derivatives (UK)
Rendered carcass material (I could not find a precise description)

Meat meal (US)
Rendered meal (dry) made from animal tissues. Does not include blood, hair, hoof, horn, skin, manure, stomach or intestinal contents, except for those small amounts unavoidably included during processing (contaminants). AAFCO define "meat meal" as "the rendered product from mammal tissues, exclusive of any blood, hair, horn, hide trimmings, manure, stomach and rumen contents."

Meat and bone meal (US)
Rendered meal (dry) from meat and bone. Does not include blood, hair, hooves, horn, skin, manure, stomach and intestinal contents, except for very small amounts that may be unavoidably included during processing.

Mechanically Recovered Meat [MRM] (UK)
Meat (UK) obtained by mechanically stripping flesh from bones. MRM includes meat recovered using combinations of grinding, steam and high pressure. Contains bone marrow, cartilage and ground up bone.

Plant Based Ingredients

Beet pulp (US)
Dried residue of sugar beets from the sugar production industry.

Brewer’s rice (US)
Small pieces of rice kernels sifted out of the larger kernels of milled rice.

Cereal by-products (UK)
By-products of the cereal industry. Includes wheat, barley, oats, rice, rye, maize (sweetcorn), some sorghums. Sago and tapioca are considered as cereals although they are processed cassava root. (Waltham Book of Dog and Cat Nutrition)

Cereal food fines (US)
By-products of breakfast cereal production; particles of food.

Cornmeal, Corn chop, Ground corn (US)
Meal made from the entire maize (sweetcorn) kernel. Must contain no more than 4% foreign material.

Corn gluten meal (US)
Residue from the manufacture of maize (sweetcorn) syrup or starch. Gluten is a sticky substance which gives wheat starch or maize starch its tough elastic quality. It is used to bind or hold together other ingredients.

Dried kelp (US)
Dried seaweed. The percentage of salt and minimum percentages of potassium and iodine must be stated on the label.

Dried whey (US)
The thin part of separated milk, dried (powdered). Must not be less than 11% protein nor less than 61 percent lactose.

Mill run (US)
See vegetable by-products

Textured Vegetable Protein [TVP] (UK)
Made from de-fatted soya bean meal.

Vegetable by-products (US)
The residue left after the primary food product has been extracted during milling e.g. "Corn Mill Run" is a pulverized blend of maize husk and corn-cobs left over after the sweetcorn kernels have been removed.

Colors, Flavors, Preservatives and Other Additives

Chemicals with no nutritional value are added to cat food to improve its taste, smell, stability, texture or appearance. Emulsifiers bind water and fat together. Antioxidants stops fat from turning rancid. Colors and flavors make the food more appetizing for the cat and more attractive to the owner. The use of additives in food (human or pet) has increased over the last several decades, though there is now a greater demand for additive-free and organic foods.

"Flavor" on a label means just that – it must taste like the named item. In the US, foods labeled "beef flavor" might contain cow by-products, but not those parts a human would term "beef". In the UK, the regulated terms "flavor", "flavored" and "natural flavor" are a confusing minefield. Natural-tasting flavors can be produced chemically in a laboratory and bought in drums. There is much debate over "artificial" or synthesized flavors which are chemically identical to the natural version, and possibly safer to consume due to purity and fewer natural contaminants.

A cat food label may simply state "artificial color" or may list a series of E-numbers or names. Colors derived from coal-tar derivatives are possible carcinogens or may interfere with the immune system. The red color Sodium nitrite (also used as a preservative) contains toxic nitrosamines. Pets may be eating more color in their diet than would be allowed in the human diet.

Cat foods must be preserved to keep them fresh and tasty. Canning is a preserving process, so canned foods need fewer preservatives than dry food. Some preservatives are added to ingredients or raw materials by the suppliers; others are added by the cat food manufacturer. Dry foods require a long shelf life; the fats in them require antioxidants, but there is relatively little information on their toxicity over a long period of time. Rancid fats, an ingredient in pet food, are often preserved with BHT/BHA and ethoxyquin, to prevent further deterioration. BHT/BHA may be carcinogenic (cause cancer). The preservative propylene glycol has a drying effect on stools and can increase constipation.

Some "harmless" chemicals are toxic to cats due to the way their livers work. The preservative ethoxyquin used in dog food has never been tested for safety in cats, one more reason cats should not raid the dog’s bowl. Ethoxyquin was developed as a rubber stabilizer and herbicide similar to Agent Orange. It is no longer used in human foods. In humans, exposure to ethoxyquin may cause liver/kidney damage, skin cancers and leukemia, hair-loss, sight loss, fetal abnormalities and chronic diarrhea. In animals it may additionally cause immune deficiencies, spleen, stomach and liver cancer.

When moist foods which required no refrigeration first appeared, vets knew they must contain a strong preservative. The preservative was formalin – an embalming agent used by undertakers and for pickling animal specimens in the laboratory (e.g. the pickled animal fetus in its jar in school science class). Nowadays, some "natural" or "organic" products use natural preservatives; as with flavors, these natural preservatives may be made in the laboratory, not harvested from plants. Foods with natural preservatives have a shorter shelf life than those with artificial preservatives.

Cats have limited ability to taste sweetness, but sweeteners in cat food masquerade under a variety of names: beet pulp sugar, glucose, sucrose (regular sugar), corn syrup or molasses. They are not necessarily used to make the food taste sweet. Corn syrup is a "humectant and plasticizer" i.e. gives the product dampness and flexibility or chewiness. Diabetes is increasing in cats – this may be linked to the consumption of sugar by a creature which does not require it in such great amounts. Added sugar can affect the absorption of other nutrients and can affect bowel fauna. Artificial sweeteners may be linked to aggression and hyperactivity. It is alleged that (unidentified) US cat food manufacturers rely on sweeteners to help "addict" cats to dry foods. This may simply be an urban legend as there was a similar scare about a cat food company adding amphetamines to addict cats to its brand of canned food.

Salt is used to increase palatability but excessive salt intake causes hypertension and kidney problems. A balance of sodium is vial for cellular health, but excessive amounts can damage these structures. Salt is added to dry food to stimulate the cat to drink and reduce likelihood of urinary blockages. Where the salt used contains iodine, this may be linked to the increase in hyperthyroidism in cats.

Cat food, and cat food ingredients, contain various additives. No-one yet knows how all these additives react together or whether they are toxic when combined. Below is a list of pet food additives; it is not comprehensive and it varies from brand to brand and from country to country.

Pet Food Additives

  • Anticaking agents – Keeps dry ingredients (flour, salt) free-flowing, prevents clumping
  • Antimicrobial agents – Prevents growth of bacteria
  • Antioxidants – Preservative, prevents spoiling
  • Coloring agents – Turns murky brown slurry/meal a more appetizing color!
  • Curing agents – Preservative
  • Drying agents
  • Emulsifiers – Binds water and fat together so they do not separate
  • Firming agents – Turns slurry into a meaty or jelly texture
  • Flavor enhancers – Modifies flavor, may do this by chemical effect on brain itself!
  • Flavoring agents – Adds flavor to unappetizing slurry/meal
  • Flour treating agents
  • Formulation aids – Help at various stages in recipe
  • Gelling agents – Turns slurry into a meaty or jelly texture
  • Humectants – Makes the food taste moist.
  • Leavening agents – Raising agent used in flour
  • Lubricants
  • Non-nutritive sweeteners – Sweetener which adds no nutritional value.
  • Nutritive sweeteners – Sugars!
  • Oxidizing and reducing agents – Used in rendering, processing and cooking.
  • pH control agents – Control pH of food or modify pH of urine.
  • Plasticizers – A texturizer – for chewiness and some reformatted meat products
  • Processing aids – Used only to aid or ease the manufacturing process
  • Sequestrants
  • Solvents, vehicles – Dissolve flavoring or coloring so they are evenly distributed
  • Stabilizers, thickeners – Stop food separating, curdling or breaking down; thickens food
  • Surface active agents
  • Surface finishing agents
  • Synergists
  • Texturizers – Modifies texture of food e.g. by affecting proteins

Diet-Related Problems

Wild cats eat primarily protein. Domestic cats eat more carbohydrate as cereals (cheap) are processed to make them as digestible as meat (expensive). This abnormal diet can lead to chronic digestive problems and inflammatory bowel disease. Dry cat food produces a hard, low-volume stool which may lead to constipation. Canned cat food produces a bulkier stool, but can cause dental problems. Cats are eating ingredients they would not normally eat and may develop allergies or food intolerance, just as the increase in peanut allergy in the UK has been linked to greater use of peanut oil.

In the US, food containing lamb or rabbit are often promoted as allergy free because these are not common ingredients in cat food. In the UK, these among the commonest ingredients and venison is allergy free. There is now a huge market for hypoallergenic cat food. These are variously labeled as "selected protein", "limited antigen" or "novel protein" They either contain ingredients not used in regular cat food (e.g. venison in the UK, lamb/rabbit in the USA) or the ingredients may have had their proteins "chopped" (chemically or by extreme pressure cooking) into fragments smaller than can be recognized by the cat’s immune system.

Owners are often recommended to feed portions larger than is actually required. Food is wasted (goes stale) so the owner buys more food. The cat food company increases its sales. However, because some cats eat when bored, feeding larger portions can cause obesity – a growing health problem for cats. In contrast, the manufacturer of one dry cat food claimed it was less expensive to use its food and recommended an amount which were independently assessed as being inadequate to maintain health. I have some of this food and it was supplied with a novelty scoop showing just how little my cat needed each day. Unfortunately my cats disagreed with this amount because they did not "feel full" after a meal. If given more because they are still hungry, they will become obese. Compact cat foods are convenience foods (lighter to carry, easier to store, less odor, smaller stools) aimed at the consumer, not at the cat.

To combat the increasing problem of obesity, there is a wide range of cat food for "less active" cats. These contain more fiber. Fiber is a cheap filler but "weight control" cat foods are more expensive than regular cat foods. There are also special formula food for "senior" or "older" cats. There are also special "growth" foods for kittens. These foods are supposedly geared to the digestive system and nutritional needs of cats of certain ages. They are more easily digested and are more expensive. Owners who can’t afford them feel guilty. Until the advent of life-stage cat foods, most older cats did fine on a good brand of regular cat food and most regular cat foods are nutritionally complete for kittens.

Urinary tract disease has been related to diet. Plugs (soft plugs of struvite and cellular debris), gravel, crystals and stones (calcium oxalate) may be triggered or aggravated by diet and the pH of the urine. Reformulation has reduced this problem by containing pH adjusting agents, but as stones have decreased in frequency, soft urinary plugs are becoming more common. One early UK brand was notorious for the urinary problems it caused before it was reformulated. Inadequate potassium has caused kidney failure in young cats; potassium is now added in greater amounts to all cat foods. A British vet told me that an early dry cat food was nicknamed "Gone Cat" by members of his profession.

The feeding of cat food which is incomplete (not nutritionally balanced) will cause disease. Taurine deficiency leads to blindness and, if not rectified, death. Taurine-deficient cat foods occur because animal protein ingredients are decreasing and carbohydrates are increasing. Cats cannot make taurine in their own bodies and taurine comes from meat. Hyperthyroidism in cats is on the increase and may be linked excess iodine in cat foods. There are claims that hyperthyroidism first surfaced in the 1970s when canned food arrived.

How is Cat Food Tested?

In the USA, feeding trials are no longer required for a food to meet the requirements for labeling a food "complete and balanced". Most manufacturers perform palatability studies when developing a new pet food. Some companies do use feeding trials; these provide a more accurate assessment of the actual nutritional value of the food. The manufacturer may have several colonies of cat including neutered and unneutered cats and a wide age range. Some companies contract this work to laboratories, those laboratories may be involved in other forms of animal research (medical or cosmetic) and some kill and dissect some of the cats after the feeding trial to assess the condition of the gut.

One by-product of food testing trials is kittens. Feeding levels for pregnant or lactating cats, and for their kittens when weaned, must be established. Though the cats are not bred inhumanely (it is not a kitten mill), those litters of kittens contribute to the increasing pet overpopulation problem; even if homed to staff or their families, they are depriving a shelter kitten of a home. There may be a problem of inbreeding after several generations.

In recent years, some European cat food manufacturers have consolidated their operations in one country, closing their manufacturing and testing plants elsewhere. This means that entire colonies of indoor cats (British and European cats are normally indoor/outdoor pets) must be rehomed or euthanized.

Fungal and Bacterial Contaminants

By-product meal and slurries may be contaminated with bacteria, especially if the raw ingredients includes animals which died because from disease, injury or natural causes. The carcass might not be rendered immediately on arrival at the plant; decomposition might have begun and bacteria such as salmonella and escherichia coli may be multiplying. Cooking may kill bacteria but may not eliminate the toxins those bacteria produce. In the US and Canada, the Salmonella Education/ Reduction Program was formed under the auspices of the National Renderers Association. Despite this, renderers continue to ignore the salmonella issue and it may require government enforcement and inspections to reduce the incidence of salmonella in their products.

Wheat can be affected by a fungus which produces a toxic substance (mycotoxin or aflatoxin). Some toxins are "heat stable" which means they survive cooking. Some cause vomiting, others can cause death. The human disease "St Vitus Dance" was caused by eating bread made from wheat which was affected by ergot, a fungus. Cooked rice can be affected by bacillus cereus, a bacteria which produces a heat stable toxin. Food poisoning in takeaway meals is often due to B cereus since the rice is cooked and stored in bulk. Ingredients most likely to be contaminated with mycotoxins are grains (wheat, maize), cottonseed meal, peanut meal and fish meal.

The British pet Food Manufacturers Association (PFMA) uses plant based substances in pet foods and highlights several aspects of quality control and inspection where vigilance is required. Plant based substances are carefully monitored for mycotoxins and pesticide residues. PFMA members specify that raw materials be free of these substances and carry out supplier audits to enforce this.

Dry cat food is sterile while being extruded, but can become contaminated with bacteria during drying and packaging. While the food is dry, the bacteria are dormant. If the packaged food is stored in damp conditions, the bacteria multiply. Adding water or gravy to moisten dry food reactivates the bacteria. If the food is allowed to stand, the bacteria multiply. Moistened kibble must be treated as though it is canned food and cleared away once the cat has eaten his or her fill.

Hormones, Antibiotics and Euthanasia Chemicals

The heavy use of hormones, steroids and antibiotics, in farm animals, is a serious concern. These continue to be active, even in "dead" tissues. For one thing, the indiscriminate or routine use (preventative use) of antibiotics has led to an increase in antibiotic-resistant bacteria. Bacteria multiply and evolve quickly, adapting quickly to an environment awash with antibiotics. Pigs, sheep, cattle and chickens are killed by physical methods (electrocution or blunt trauma). Cats and dogs from shelters will most likely have been killed using chemicals which may not be destroyed by rendering and which may enter the food chain.

Sodium pentobarbitol, a barbiturate, is used to euthanize companion animals and some larger pets such as horses. This drug should not be used on animals intended for food, though carcasses of horses or deer destroyed by injection may be fed to hounds in hunt kennels (hounds are destroyed at a relatively young age i.e. when they slow down). In studies conducted at the University of Minnesota, USA, it was found that sodium pentobarbitol survived rendering without undergoing degradation. This means that the drug can enter the food chain in exactly the same form as it was injected into an animal to kill it. It is not currently known what effect this drug has when pets consume pet foods contaminated with this drug.

In 1985, the American Journal of Veterinary Research carried out an investigation into the persistence of the euthanasate sodium phenobarbital in the carcasses of euthanized animals at a typical rendering plant. They found that it survived a conventional rendering process. This means that other chemical contaminants (e.g., heavy metals, pesticides, hormones, antibiotics, organophosphates etc) may also survive the process largely unchanged.

Prion Disease

BSE (Bovine Spongiform Encaphalopathy) can be transmitted by feeding ground up cattle to other cattle. It may have originated from feed scrapie-infected sheep to cattle though recent investigations suggest that it is traceable to an imported antelope at a zoo. Zoo animals also end up at rendering facilities. A feline version of BSE, called FSE, has already been reported in Europe. Some bovine tissues are believed to pose a greater risk than others. Bovine materials now banned from the food chain (Specified Bovine Offals) includes the head, spleen, thymus, tonsils, brain, spinal cord, small and large intestines. These must be segregated and incinerated. The materials are now called Specified Risk Material and includes material from sheep and goats as well as from cattle.

In Britain, the PFMA policy towards Specified Bovine Offals was ahead of the policies in the human food industry. In June 1989, PFMA members adopted a voluntary ban on the use of the specified bovine tissues. This was a precautionary measure prior to the Ministry of Agriculture, Fisheries and Food’s introduction of a ban on the use of these bovine materials for human consumption in November 1989 and a subsequent ban on their use in animal feed in September 1990. In the US, it is believed that transmissible spongiform encephalopathies (TSE) carried in pig- and chicken-laden foods may eventually eclipse the threat of BSE. The risk of household pet exposure to TSE from contaminated pet food is more than 3 times greater than the risk for hamburger-eating humans. In the UK, specified materials are not used in pet food. There may be other diseases not yet seen in cats and dogs because they do not routinely cannibalize members of their own species.

Foreign Bodies

Inedible items find their way into the mix for various reasons. Some are loaded into the grinder attached to carcasses, some are part of the stomach contents or is inside the animal e.g. shot from a gun. The British PFMA recognizes that plant materials are often accompanied by foreign bodies from the soil so its members use cleaning systems such as screens, magnets and metal detectors.

In the US and Canada, non-food items apparently routinely end up in the rendering pit – cattle insecticide patches, carcasses full of antibiotics, ID tags and surgical pins, spoiled supermarket meat still in cardboard, styrofoam trays and shrink wrap and pet body bags. It is simply to costly and time consuming for staff to remove these items. Some (e.g. metal objects) are filtered out, but other melt into the mix and may form toxic compounds. A Massachusetts Institute of Technology study, titled "Lead in Animal Foods", found that a nine-pound cat fed on commercial pet food ingests more lead than the amount considered potentially toxic for children.

Road Kill, Racehorses and Zoo Animals

In some countries, large road kill is recycled into pet food. This makes some sense, particularly if the road kill is a recognized food species such as deer. As well as road kill, some rendering plants (not in the UK) which supply cat food manufacturers have reportedly added such diverse things as a circus elephant, zoo animals, police horses, wild horses (in some areas they are considered a serious pest), kangaroo and even cats and dogs from animal shelters.

There is no doubt that zoo animals and circus animals must be disposed of somehow. One theory about BSE suggests that it can be traced to an antelope from a zoo, meaning that prion disease may have been imported into Britain from Africa. Horsemeat is not used in British pet-foods so every year hundreds of British wild ponies are exported to European countries where there is no horsemeat taboo. In the US and feral horses (mustangs) and feral donkeys (burros) have been used in pet foods. Australian wild horses (brumbies) are culled as serious environmental pests and there is potential for recycling the culled horses. Every year, hundreds of racehorses, show-jumpers and riding school horses/ponies are "retired". Rendering is an efficient way of recycling their carcasses.

Each year hundreds of greyhounds are "retired" or fail to make the grade. It is suspected that many end up at rendering plants, either openly or secretly. There are unconfirmed rumors that victims of gangland killings are sometimes disposed of in the same way. It is my understanding that laboratory animals must be incinerated as "medical waste" because they were used for drug tests, cosmetic trials or were deliberately infected with disease.

Domestic Pets

It seems macabre, but in some countries cats and dogs are recycled into pet food and livestock feed. Rendered pets are just another source of protein. Some American vets believe that the use of pets in pet food is routine practice. Rendering is a cheap viable means of disposal for euthanized pets which can be mixed with the other slaughterhouse products unfit for human consumption, rotten meat from supermarket shelves, so-called 4D animals (Dead, Diseased, Dying, Disabled), road kill and other animals. No pet owner will see listed ingredients such as "raccoon meat" or "cat by-products" and most recycled pets end up in fertilizer (meat and bone meal). Since the rendering plant labels each batch according to the predominance of a specific animal, it doesn’t mean that other animals were not in the mix in small quantities.

According to American veterinarian Fred Bisplinghoff, Consultant for the Animal Protein Producers Industry (APPI) the belief is unfounded. He says that adverse publicity and scare stories have dictated that renderers get rid of small animals or make arrangements to sell their end products into markets other than the pet-food market. Rendering is an economical, environmentally sound way of disposing of pets. The alternatives, necessary where rendering operations do not process pet carcasses, are burial or incineration – expensive and polluting. In the UK, euthanized animals are classed as medical waste and incinerated. There are also incineration facilities which deal only in infectious animals which cannot be rendered (e.g. BSE) In my own locality a local pig farmer has an incinerator and he incinerates pets and road kill sent by vets and local authorities.

John Eckhouse, of the San Francisco Chronicle, wrote about the recycling of pets into pet-food in California. He claimed that pet food companies deny it while a rendering industry employee claimed it to be common practice for his company to process dead pets and sell the products pet food manufacturers. The Food and Drug Administration, Center for Veterinary Medicine (FDA/CVM) recognizes a need to dispose of pets in large numbers and does not specifically prohibit the rendering of pet carcasses.

According to veterinarian Tim Phillips, rendering pets for pet-food is not harmful to pets consuming such pet-foods. Emotional reactions overshadow any rational discussion of this issue. The rendering industry is well aware of public disapproval of the practice and only a few process companion animals. Since the rendering plants only have to name the main ingredient in a run, the pet food manufacturer buying the product may not about the hidden extras – not just pets, but also inedible items.

In investigations in the US and Canada, Eckhouse learnt that the pets are rendered complete with their collars, tags, flea collars and still inside plastic pet body-bags. Chemicals from plastic and organophosphates from flea collars end up in the mix along with a host of other substances. Pharmaceuticals leak from antibiotics in diseased livestock. Heavy metals accumulate from a variety of sources: pet ID tags and surgical items (e.g. bone pins). Unsold supermarket meats arrive in Styrofoam and plastic containers. It is too costly and time-consuming to remove flea collars or unwrap spoiled meat. More plastic is added to the pits with the arrival of cattle ID tags, plastic insecticide patches and pet body bags from veterinarians. Plastic contains estrogen-like substances which may survive rendering and lower sperm count in male animals.

In the USA, there are various type of rendering plant. Of these, only the independent renderers might process dead pets. Bisplinghoff believed that of 182 independent renderers in the USA (at the time of the study), only 5-7 processed pets, though this number omitted small country processors who may occasionally take a pet from a livestock producer. Protein blenders purchase dry rendered tankage from other rendering plants and may unknowingly buy rendered pets. Small feed companies were not considered as they do not manufacture companion animal diets.

American Pet-food manufacturers are large volume, highly valued customers. They require a guarantee that their animal protein suppliers do not process dead pets. Bispolinghoff believed that renderers supplying pet food manufacturers would not want to risk this profitable business. In addition, he considered that dead pets are not desirable raw material for rendering and there is little or no economic incentive for renderers to seek this type of raw material. However, some renderers process pets from animal shelters in order to satisfy local health authorities seeking an economic and sanitary disposal method. The few American renderers who handle large volumes of dead pets are not suppliers to the pet-food industry, they either export their animal proteins or sell them to poultry operations. Your own pets might not be eating dead pets, but the chicken on your plate or the chicken that laid your breakfast eggs might well have eaten dead pets.

Other reports contradict Phillips and Bisplinghoff’s beliefs that it is uneconomical to render pets. It all depends on how many surplus pet animals there are. In 1996, Earth Island Journal reported that a small rendering plant in Quebec (possibly Sanimal) rendered 10 tons (22,000 pounds) of dogs and cats per week from Ontario; the fur was not removed and the carcasses were cooked at 115 Celsius (235 Fahrenheit) for 20 minutes. There must, therefore, be some economical incentive to process dead pets and road kill. Eileen Layne of the CVMA (Canada) said that when the public read pet food labels saying "meat and bone meal", what it really means is "cooked and converted animals, including some dogs and cats." Protein derived from pets and road kill is hidden as "meat meal", "meat by-products" or simply "animal protein".

One large pet food company in the U.S., with extensive research facilities, allegedly used rendered dogs and cats in their foods for years. When the public became aware of this, the company apparently pleaded ignorance. The US Food and Drug Administration, Center for Veterinary Medicine (CVM) is aware of the use of rendered dogs and cats in pet foods and stated that they neither prohibit not condone the practice.

The Earth Island Journal reported that Baltimore’s "Valley Proteins" rendering plant processed dead dogs and cats and road kill alongside livestock and horses, producing a dry protein product to be sold in the pet food industry. Baltimore’s animal pound disposed of more than 21,888 dead animals (approx 1800 per month) to Valley Proteins. Valley Protein was reported to have two production lines – one for "clean" meat and bones and a separate one for dead pets, road kill and suchlike. The final protein material was a mix from both production lines which means that rendered pets could potentially be sold to manufacturers of dry pet-food.

Valley Proteins confirmed that their Baltimore plant processed pets euthanized by vets, animal control officials, humane societies, animal shelters etc. Domestic pets represented less than 0.5% of the plant’s annual business. In a 12 month period, one pet food producer purchased approximately 10 tons of rendered protein from the Baltimore plant on 3 different occasions. This represented less than 0.5% of the total Baltimore Meat Meal production, meaning that approximately 300 pounds of animal protein containing by-products from cats and dogs ended up as cat and dog food. Apart from those 3 instances, the pet food manufacturer was supplied by other Valley Proteins plants which rendered poultry by-products.


Depending on which country you live in and how strongly it regulates the pet food industry (if you have a pet food industry), the contents of pet food will be a far cry from the appetizing picture in the advert.

That plump chicken could mean that the pet food contains ground up beaks and feet, packaged supermarket meats (complete with the wrapper) and dead birds from battery egg producers. A prime juicy steak? Or the cow’s head, hooves and udder? Instead of boiling up fish heads ourselves, we buy our fish heads in canned or kibble form, complete with a picture of silvery-scaled fresh caught fish. I am not saying that the food is unhealthy – just that you are not buying what you might think you are buying. In some countries, cat and dog food packages have illustrations of cats and dogs on them – this could be an accurate reflection of what the food contains.

In most countries, pet food manufacturers produce high quality, nutritionally complete foods for our pets, formulated to keep them in good health. Commercial pet foods are convenient to buy, store and use. This is the bottom line – commercial pet foods are there for human convenience. Just so long as you don’t think to hard about what is inside the can – or how it got there – you won’t lose any sleep.