There is nothing wrong with the "icky bits" of an animal. Offal contains vital nutrients. In the wild, cats eat the skin and stomach contents of their prey. Humans eat the icky bits unknowingly in sausages, meat pies and meat pasties (and other reformatted meat products). Pet food manufacturers have years of experience in making nutritionally complete cat foods. It must approximate the nutritional content of "whole chopped mouse" - icky bits and all!

In some places, ground-up cats and dogs can end up in pet food. Rendering carcasses from animals shelters or roadkill is an efficient, environmentally-friendly disposal method. Sanimal of Quebec, Canada mostly process pig and chicken, but also rendered over 18,000 kg of cat and dog flesh weekly. The resulting protein meal was sold to the animal feed industry. In spite of stating the food was healthy while people were squeamish about "cannibal" pet food, Sanimal stopped rendering domestic animal carcasses. Rendering is less polluting than disposal by remation 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 polluted by acrid smoke, charred scraps floated from pyres and fluids leaked from burial pits. The question is not "should cats and dogs be rendered" but "should the rendered product be fed back to cats and dogs". Cannibalism offends our sensibilities, especially after the BSE crisis in Britain.

Britain was plagued with BSE 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 are genuine health concerns about feeding animals back to members of their own species.

What is in pet food and how it is manufactured is easily found via news reports, animal welfare society reports, vet conferences and reports from pet food manufacturers themselves. I originally studied this topic for a University term paper as an adult student in the late 1980s and grossed out the lecturer! This is an expansion of that term paper. The Waltham Book of DOg and Cat Nutrition proved an invaluable source of information.

Note: There are two important things to bear in mind regarding what goes into cat food. Firstly, many humans observe taboos over which animals and which parts of those animals can be eaten - or even whether animals should be eaten at all. Cats have no such taboos. Imposing human taboos on cats may result in nutritional problems. Secondly, to supplement their hunting, free-living cats will scavenge dead animals, roadkill and garbage. They will eat cats and dogs just as they will eat rabbit. Cats (and dogs) found trapped inside houses with their dead owners will even eat parts of the owner in order to survive.

Note 2: This article was updated in 2008 noting that many pet food manufacturers in the USA are no longer using sources of meat that had previously given cause for concern.

Rendering is the process of processing raw animal material (carcasses) on an industrial scale to remove moisture and fat. Some plants produce "highly pigmented meat slurry" while others produce a dry product. 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 meat slurry 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 ground into small pieces. This is a larger version of the old table-clamped meat grinder used in the days before food processors. The roughly round pieces are moved 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 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 pulverises 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.

The primary products of the food industry are the meats that end up on human dinner tables. By-products are the secondary or incidental products out of this process, including internal organs, feathers and hair. These can be hydrolysed (pressure cooked with steam to form an edible gel) and become "poultry by-products" and "meat by-products" in pet food.

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 labelling 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".

One category of raw materials is known in the US as "4D animals" i.e. Dead, Diseased, Dying, Disabled and in the UK as "condemned". Some died or are dying from unknown causes and may have been treated with various drugs, possibly including a euthanizing drug. The meat from these animals can be sold for pet food after it is completely covered in charcoal or non-toxic dye (to prevent ingestion by humans), and marked "unfit for human consumption". If the 4D animals are already decomposing, they go straight for rendering. Undercover operations in the UK (as seen on "Life of Grime" and "Food Police") found that some decaying carcasses got cleaned up and laundered back into the human food chain by unscrupulous packagers.

Update 2008. Since the initial reports and public concern, the Food & Drug Administration (FDA) in the USA analysed samples of pet food looking for the euthanasia drug pentobarbital. The ingredients in which it was detected were meat-and-bone-meal and animal fat. 4D animals (dead, dying, diseased, disabled) have now been banned from human consumption, but remain legitimate ingredients for pet food, however reputable manufacturers may avoid using these in the same way they now avoid using rendered pets/roadkill.

In some countries, roadkill too large to be buried along the roadside is sent for rendering rather than landfill. This is an efficient method of disposal. Condemned material from slaughterhouses goes for rendering: animals that died in transit, diseased animals or animal parts and those parts of the animal (blood, hair, heads, feet) unsuitable for human consumption though 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 (composition secret); in the US carbolic acid (potentially corrosive disinfectant, toxic), creosote (wood-preservation, disinfectant, toxic), fuel oil, kerosene and citronella (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 products not fit for human consumption were very well sterilised so that nothing could be transmitted to the animal. However, in the UK, cattle feed was believed to be very well sterilized until BSE emerged; the causal agent was not destroyed at the sterilizing temperature. The size of the rendering batches greatly dilute any drugs or chemical substances which may be present in the source animals.

About 50% of a food-producing animal is not used in human food. These "by-products" include bones, blood, intestines, many internal organs, ligaments, hooves and rind and are used in animal feeds and fertilizers. They are not necessarily unhealthy or inedible, just unpalatable to modern palates. 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 (still the fate of large roadkill and riding horses in rural areas). Many towns had a "cat's meat man" who sold skewers of waste meat to cat owners for a couple of pennies.

A current concern to owners is the use of cloned and GM animals. Cloning animals is currently too expensive to be practical for food production, but farmers could clone top-quality animals as breeding stock. Food products and by-products from the offspring of clones and from clones themselves will be indistinguishable from that from normally conceived animals and, in the US at least (where the powerful food producers' lobby groups render food safety groups largely impotent), will not need special labelling as to its origin.

In the USA, food animals are routinely dosed with antibiotics, anabolic steroids and growth promoting hormones prohibited in Europe. The residue of these chemicals enters the food chain and can cause allergic reactions (and probably less obvious effects) in humans and pets. In Britain, pigs were once routinely dosed with penicillin and the drug residue ended up in pork products; my uncle, who was allergic to penicillin, suffered allergic reactions to sausages made from pigs medicated with penicillin. Similar allergic reactions might be overlooked in pets. The antibiotics are used because animals reared in intensive conditions suffer disease through over-crowding and from wading through their own waste products (the latter results in the higher incidence of harmful E coli strains). As a result of widespread antibiotic use, antibiotics are now present in low levels in the environment and resulting in ever-stronger bacteria - the so-called super-bugs - through mutation and natural selection.

"Organic" petfoods (or at least those with organic ingredients) are on the increase. Organically reared animals are reared without the routine use of antibiotics; without growth-promoting hormones and cannot be genetically modified (GM) animals. Organically produced crops (most cat food contains plant byproducts) are non-GM and grown without using conventional pesticides, artificial fertilizers or sewage sludge. Organic foods are processed without ionizing radiation or food additives. Britain, Canada, USA, Australia and Japan all have bodies able to certify foods as organic. Organic foods do not contain the chemical residues found in some conventionally produced food and this may benefit the consumer as well as the environment. However it is more expensive to produce and there are concerns over food safety especially residues of organic pesticide residues.

Supporters of organic petfoods suggest that many of the digestive problems, skin conditions and even behavioural problems in pets could be due to chemical residues in their food. Within the European Union, pet owners should be cautious of imported petfoods and of petfoods made with meat products sourced from countries where growth promoters and antibiotics are routinely used . In general, European Union countries place far more emphasis on testing food animals and slaughterhouses for pathogens (e.g. E coli, salmonella, BSE) while American food producers resist the routine testing of animals and processing plants for these pathogens (US meat produces continue to resist routine testing for BSE). As a result, many European pet foods may actually be safer (i.e. the meat more stringently tested and controlled) than American fast foods.

Note: An excellent factual text about food production methods in the USA is "Fast Food Nation" by Eric Schlosser. "The Food Scandal" by Caroline Walker and "The Meat Machine" by Jan Walsh look at food processing methods in the UK (the latter two books are now only available second hand). Although the books were written about the human food chain, pet foods contain by-products from the the animals raised to feed humans.

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 labelling of pet food. Pet food labelling is described later.

In the US and Canada, the pet food industry is virtually self-regulated. In the US, the Association of American Feed Control Officials (AAFCO), in association with the Petfood Institute (PFI) sets guidelines and definitions for animal feed, including pet foods. Uner the 1987 Uniform Feed Bill, PF1 coverened definitions and terms; PF2 covered labelling and label format; PF3 covered brand and product names; PF4 covered expression of guarantees; PF5 covered ingredients; PF6 covered directions for use and PF7 covered drugs and additives in pet foods.

EEC equivalents are 70/524/EEC covering additives in all feeds, including prepared pet feeds; 74/63/EEC covering the maximum permitted levels for undesirable substances and products in feedingstuffs; 79/101/EEC covering the marketing, labelling and distribution of straight feedstuffs and 79/373/EEC covering the marketing, labelling and distribution of compound feedingstuffs.

In Canada, regulation of the pet food industry is poorer. 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 labelling and regulating the pet food industry. The Waltham Book of Cat and Dog Nutrition warns that the AAFCO protocols are "the minimum necessary to substantiate particular product nutriional claims and more complex testing is frequently undertaken by some manufacturers in order to ensure life-long health". I have no information about pet food regulatory bodies in other countries.

Most countries have food labelling 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 labelled "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 labelled "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, entrée(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 labelling. Pet food labelling 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.

AAFCO define a complete food as "a nutritionally adequate food for animals other than man; by specific formula is compounded to be fed as the sole tation and is capable of maintaining life and/or promoting production without any additional substance being consumed except water." The 1979 EEC Feedingstuffs Regulations governing animal feeds define a "compound feedingstuff" as a "compound feedingstuff which by reason of its composition is sufficient to ensure a daily ration" where "daily ration" is defined as the quantity of feedingstuff, expressed on a 12% moisture basis, required to satisfy average daily nutritional needs of the specified type and kind of animal. The UK Feedingstuffs Regulations (1986) define "complementary feedingstuff" as a compound feeding stuff whose composition is not sufficient to ensure a daily ration unless used in combination with other feedingstuffs.

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, fibre 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 colourants 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 analysing 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 labelled 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).

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 fibre 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 flavour 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 flavourings.

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.

Many vets and owners have suspected a link between canned foods, particularly fish flavours, and the increase in feline hyperthyroidism. It is currently suspected that the cause is a thin plastic lining found on pull-top cans. According to my vet, feline hyperthyroidism was either rare or underdiagnosed twenty years ago compared to now.

Note: "The Waltham Book of Cat and Dog Nutrition", Chapter 4 is an excellent resource on the manufacturer and constituents of cat food. "The Food Scandal" is an excellent resource on rendering and reclamation of meat from carcasses.

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 (though electrocution or blunt trauma methods are more usual in slaughterhouses). Even less desirable contaminants also may enter the product.

To make the naturally bland kibble appetizing to cats, it is sprayed with fat mixed with flavour enhancers. 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 diarrhoea 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 fibre - think about it, they are used in some bean bag toys!

Even wood ("cellulose", "cellulose pulp") can be an ingredient. 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 gives common pet food and meat industry labelling terms (available from AAFCO (US) and PFMA and Waltham (UK)). 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. The definitions of meat by-products, poultry by-products and poultry by-products are taken from AAFCO industry-standard definitions and are minimum standards; manufacturers of good quality brands will exceed these standards.

Non-nutritional chemicals re 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. Colours and flavours make it look or taste more appetising. 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 such as Denes.

"Flavor" on a US label means it must taste like the named item; "beef flavor" might contain cow by-products, but not prime steak. In the UK, the regulated terms "flavour", "flavoured" and "natural flavour" are a confusing legal minefield. Natural-tasting flavours can be produced chemically in a laboratory and bought in drums. There is much debate over "artificial" or synthesised flavours 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 colour," may list several E-numbers or (to bypass suspicion of E-numbers) several names of dyes. Colours derived from coal-tar derivatives are possible carcinogens or may interfere with the immune system. The red colour Sodium nitrite (also used as a preservative) contains toxic nitrosamines. Pets may be eating more colour in their diet than would be allowed in the human diet. In humans, artificial colourings may be linked to hyperactivity.

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, another reason cats should not eat dog food. Ethoxyquin is no longer used in human foods. It was developed as a rubber stabilizer and herbicide similar to Agent Orange and may cause liver/kidney damage, skin cancers and leukaemia, hair-loss, sight loss, foetal abnormalities and chronic diarrhoea. In animals it may also cause immune deficiencies, spleen, stomach and liver cancer.

Moist foods that require no refrigeration must contain preservatives. Originally this was formalin, used in embalming and in pickling animal specimens (e.g. the pickled animal foetus in its jar in school science class). Nowadays, some "natural" or "organic" products use "natural preservatives" though these may be synthesised in the laboratory. Foods with natural preservatives have a shorter shelf life than those with artificial preservatives.

Cats have limited ability, if any, to taste sweetness, but sweeteners are still found in cat food: beet pulp sugar, glucose, sucrose, corn syrup or molasses. They are not necessarily used to make the food taste sweet. Corn syrup is a "humectant and plasticizer" i.e. makes food moist and chewy. Diabetes is increasing in cats and may be linked to the over-consumption of sugar. Added sugar also affects the absorption of other nutrients and can affect bowel fauna. Artificial sweeteners may be linked to aggression and hyperactivity. It is alleged that unscrupulous cat food manufacturers rely on sweeteners to "addict" cats to dry foods in the same way that one company was alleged to add amphetamines to addict cats to a brand of canned food.

Salt increases palatability but excessive salt intake causes hypertension and kidney problems. A balance of sodium is vital for cellular health, but excessive amounts are damaging. Salt is added to dry food to stimulate the cat to drink and reduce likelihood of urinary blockages. Iodised salt may also 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.

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 labelled 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 odour, smaller stools) aimed at the consumer, not at the cat.

While it is commonly stated that canned food causes bad teeth, it is a fallacy that dry food (kibble) will keep teeth clean. Tearing flesh keeps teeth clean, a cursory crunch on a piece of kibble does not have the same effect. To make matters worse, any sugars in the kibble can lead to dental caries. Prey contains a mix of textures and the cat must crunch bones and shear through skin and flesh. A diet of wet food only or a diet of dry food only can both cause dental problems and a dry food diet can additionally lead to obesity.

To combat the increasing problem of obesity, there is a wide range of cat food for "less active" cats. These contain more fibre. Fibre 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.

In the USA, feeding trials are no longer required for a food to meet the requirements for labelling 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.

More information of the content and testing of feline diets can be found in The Waltham Book of Dog and Cat Nutrition and The Waltham Book of Clinical Nutrition of the Dog and Cat (Waltham Centre for Pet Nutrition) (Josephine Wills and Kenneth Simpson) .

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.

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.

Update 2008. Since the initial reports and public concern,the Food & Drug Administration (FDA) in the USA analysed samples of pet food looking for the euthanasia drug pentobarbital. The ingredients in which it was detected were meat-and-bone-meal and animal fat.

See Cat Food Contamination for a detailed report in to the 2007 melamine adulteration event.

In North America, ingredients standards appear less rigourous than in the UK. The American Food and Drug Administration (FDA) has been criticised as ineffective in ensuring the quality of both human foodstuffs and petfoods. During 2009, Nutro pet food had been the subject of articles on ConsumerAffairs.com after pets became sick or died through eating popular Nutro brand petfoods. The ConsumerAffairs website requested documents from the FDA, under the Freedom of Information Act (FOIA), regarding complaints received about Nutro pet foods. The request was denied and the FDA claimed the "document(s) constitute record(s) compiled for law enforcement purposes, the disclosure of which could reasonably be expected to interfere with enforcement proceedings." However, both Nutro and the FDA later denied there is any investigation by the FDA into Nutro products, in which case there is no reason to withhold the records requested under the FOIA. The FOIA Office, however, claimed there was an ongoing investigation into Nutro. In the face of complaints disseminated through online social networks, Nutro launched its own PR exercise.

In 2007, Menu Foods in North America recalled numerous brands of possibly contaminated canned and pouched cat and dog food following kidney-related illnesses and deaths in a number of cats and dogs. Imported wheat gluten (a binding agent in pet food) contaminated with rat poison was ruled out by the US's Food and Drug Administration. Levels of melamine were found in the gluten imported from China, but toxicologists were not certain that it was present in levels toxic to cats and dogs. Several Hills, Purina and Del Monte foods were also recalled as a precautionary measure. Melamine is sometimes added to ingredients in China to boost the apparent protein levels, but such adulteration can be lethal. There was similar obfuscation of the information when the FDA's Office of Enforcement, denied that the agency knew of any additional forthcoming pet food recalls, yet only hours later, Costco and several other companies announced the recall of several brands of pet food initiated (according to Costco) because the FDA had found melamine adulteration.

In the USA, the FOIA is supposed to allow concerned bodies to obtain information from companies. The FDA is supposed to ensure the safety of foodstuffs. In practice both seem to be creating a smokescreen that protects companies whose products are giving pet owners cause for concern and which might be contributing to the deaths of pets due to using adulterated ingredients. One safeguard would be to stop importing cheap ingredients from suppliers previously guilty of adulteration.

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. 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. A feline version of BSE, called FSE, has already been reported in Europe.

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. By contrast, in the USA in 1997, as a precaution against prion disease, the FDA finally banned the feeding of dead sheep, goats, cattle, deer, mink, elk (red deer), dogs and cats to cattle although these items were still used in pet foods. Foods containing the banned items were supposed to be labelled "Do not feed to ruminants". However, the Grocery Manufacturers of America, the National Food Processors Association and the Pet Food Institute successfully lobbied against the new labelling requirement for pet foods. They were worried that the warning would alert owners to what was really in pet food.

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 cannibalise members of their own species.

In the USA and Canada, a prion disease known as Chronic Wasting Disease (CWD) and nicknamed "Mad Elk Disease" is found in the native deer population. It was first observed in the 1960s in Colorado and affected deer and elk (red deer) in the Rocky Mountains and Plains regions and parts of western Canada. CWD has now shown up in parts of Nebraska and Wisconsin, triggering massive deer culls in 2002. Although CWD has not yet been proven to cause illness in humans or cattle, the World Health Organization recommends against eating any part of a deer showing symptoms. It is possible that cases of vCJD traceable to infected deer might show up in humans in years to come. The USA's Centers for Disease Control and Prevention (CDC) do not investigate CJD deaths in humans in areas where CWD has not previously been seen; they only investigate deaths in areas where CWD is already known to be present!

The problem with the CDC's philosophy is, if you don't test suspicious deaths, you don't find out if CWD is present or spreading and it ends up in the food chain. In the USA, large roadkill may be rendered into pet food, making CWD infected deer another potential source of prion disease. Reports in November 2002 did not state how up to 250,000 culled deer would be disposed of in Wisconsin (some will be eaten by hunters) although rendering was one option. In Europe, incineration is the preferred - and possibly the only truly safe - option.

In 1990, a Siamese cat in Bristol died of FSE at a time when 6 million cows (6,000,000) were being slaughtered because of BSE. This caused an immediate scare over the safety of pet food and the use of infected cattle in pet food. Although the press had a field day with "Mad Cat Disease", one cat does not an epidemic make. Since cats are not part of the food chain it was not a risk to humans (unlike the cattle) as the media seemed to suggest. It was, however, worrying for owners concerned that they might inadvertantly be infecting their cats - after all, we choose what our pets eat.

The cat showed symptoms of nervous disease in January 1990. It had poor limb co-ordination, but unlike BSE-affected cattle it was not nervous or aggressive. The vet even described it as "happy, but drunk". It did respond to treatment for more common nervous disorders e.g. brain tumour or thyroid disorder and was referred to the Bristol Veterinary School for further investigation. No effective treatment was found and it was euthanized in April. Brain tissue was found to have characteristics normally associated with BSE. FSE had never been reported before. If the cat had contracted the disease from its food, this must have happened before the ban on using infected cattle in foodstuffs as the disease usually take several years to appear. In December 2000 a lion at Newquay (Cornwall, UK) zoo fell ill after a fight with another lion. An autopsy revealed its death was due to FSE.

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 recognises 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.

In some countries, large roadkill is recycled into pet food. This makes some sense, particularly if the roadkill is a recognised food species such as deer. As well as roadkill, some rendering plants (not in the UK) which supply the animal feed industry may process circus and zoo animals, police and race horses, wild horses/ponies (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, but in the US 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. Similarly, each year hundreds of greyhounds are "retired". It is suspected that many end up at rendering plants, either openly or secretly. There are even rumours (or urban legends) 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.

Update 2008. Since the initial reports and public concern, repuatable manufacturers in the USA no longer use sources that contain rendered roadkill. Although not against the law to use roadkill, the practice is increasingly uncommon and reputable pet food companies are at pains to stress that they do not use these sources.

It seems macabre, but in some countries rendered pets are just another source of protein. 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), roadkill and other animals. No pet owner will see listed ingredients such as "racoon 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 by vets along with medical waste (amputated limbs, excised tumours) and incinerated; the EU's legal definition is Category 1 Animal By-Product i.e. high risk. There are also incineration facilities which deal only in infectious animals which cannot be rendered (e.g. BSE). In my own locality, dead pets are stored in the vet practice's freezer and sent to a local pig farm that has an incinerator; the pig farmer incinerates pets and roadkill sent by vets and local authorities. Other veterinarians will have their own arrangement for agencies to collect and dispose of carcasses. EU Regulation (EC) No. 1774/2002 and Animal By-Products Regulations (ABPR) 2005 (in the UK) permit either incineration or rendering of pets as they are classed as Cat 1 (hazardous) animal by-products. Following public outcry when these rules were introduced, the Government in the UK applied a special derogation to allow dead pets to be buried. Although legal to render dead pets, the PFMA only use by-products from meat in the human chain, automatically excluding pets from entering the food chain (it is not known how much, if any, is rendered for fertilizer; vets' clientele prefer their dead pets to be cremated/incinerated).

Update 2008. Since the initial reports and public concern, the Food & Drug administration (FDA) in the USA analysed samples of pet food using very sensitive tests to look for cat and dog DNA. None was found. Although not against the law to use rendered pets and roadkill, the practice is increasingly uncommon and reputable pet food companies now stress that they do not use these sources.

John Eckhouse, of the San Francisco Chronicle, had written 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(prior to the 2008 update above), 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 oestrogen-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 valuable large volume. 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 roadkill. 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 roadkill 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, Centre 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 roadkill 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, roadkill 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.

ALTERNATIVE DIETS

I am sometimes berated for not recommending one of the alternative feeding regimes currently in vogue e.g. diets devised by nutritionist as being better than commercially prepared pet foods. In countries where regulation of the pet food industry allows fillers, or where regulation is generally poor, owners may wish to consider home preparation of a diet. They are also suitable for cats with specific dietary needs e.g. food intolerances. There are several drawbacks. Even where good quality meats are selected, raw meat diets expose cats to parasites and bacteria that the canning process kills off. It is argues that cooked meat weakens the immune system, but few owners wish to deliberately expose their pets to the pathogens found in raw meat (E coli and salmonella are prime examples; E coli 0157 is now widespread in cattle and often fatal when eaten).

Feeding nothing but bones and raw meat is dangerously unbalanced and irresponsible. Misguided owners may think that it is a natural, and therefore healthy, diet. It is not. Cats have evolved to eat small prey in its entirety - skin ("animal roughage"), bones (calcium), internal organs (vitamins, minerals) and stomach contents (roughage, possibly vitamins and minerals from partly digested food). The bones of their natural prey are tiny, flexible and fragile enough to be broken by the cat's teeth. The sort of bones fed to cats by humans come from much larger prey and may splinter when crunched, causing damage to the mouth, throat, stomach or intestine (the latter often being fatal). The sort of meat fed with those bones is muscle meat with some sinew and is not nutritionally balanced. Some such diets require expensive vitamin and mineral supplements to be sprinkled on the raw meat.

In the early 1990s, the Australian "National Cat" magazine printed recommendations to feed cats raw chicken wings as a way of cleaning their teeth. I raised this as a query to vets at a Feline Advisory Bureau conference the same year. Their answer did not favour the feeding of raw poultry wings to cats due to the potential for injury.

As with the many human diets, some of the alternative feline diets are faddy and the main benefit is to the deviser's pocket. The main "evidence" for a faddy diet's efficacy may be from its promoter rather than from long-term, large group, independent trials. The word "natural" may be bandied about (deadly nightshade is natural - "natural" does not mean "healthy"). The promoter may make a considerable sum of money from selling supplements to compensate for the feeding of muscle meat and bones only. Like other premium brands not found on supermarket shelves, they may be recommended or sold through vets who earn commission on sales.

As well as feeding a potentially dangerous and unbalanced diet, a major drawback are that relatively few owners have the time needed to properly weigh out ingredients to create a home-prepared balanced diet. Owner convenience is why commercially prepared pet food was invented in the first place. Another drawback is financial, and for many this is the bottom line: commercially prepared diets are affordable (ranging from basic to deluxe) and, in a country with a well regulated pet food industry, will be appropriate for the needs of all but a few cats. Before embarking on an alternative diet, seek the advice of your veterinarian and be aware of the dangers of food poisoning and nutritional imblance/deficiency. Bear in mind that an alternative diet probably represents one individual's opinion of a cat's needs and may not have undergone large-scale feeding trials.

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.

I am often asked if I advocate a fresh meat or home prepared diet for cats. My own cats are fed on a mix of wet and dry commercially prepared cat foods. Modern regulations, in Britain at least, make this the most efficient method of feeding. The manufacturers have far more experience in getting the nutritional balance right than I have. As for whether I am worried about roadkill in pet food, my answer is "no". I don't believe in making pets observe human taboos over which animals can't be eaten, or whether animals should be eaten at all. I've seen feral cats scavenge garbage and eat roadkill. Cat rescuers have even seen cats eat the remains of other cats. Scavenging cats don't worry over how an animal died, just so long as the meat smells okay to eat, it is just another part of the food chain.

The following are not restricted to the pet food industry, but cover the meat industry in general, including the definition and use of animal byproducts.

Fast Food Nation: What the All-American Meal Is Doing to the World by Eric Schlosser
The Food Scandal: What's Wrong with the British Diet and How to Set It Right by Caroline Walker and Geoffrey Cannon
Meat Machine by Jan Walsh
National Research Council Nutrient Requirements of Cats (1986) National Academy of Science, Washington
The Waltham Book of Dog and Cat Nutrition and its successor, The Waltham Book of Clinical Nutrition of the Dog and Cat from the Waltham Centre for Pet Nutrition, by Josephine Wills and Kenneth Simpson
Tout Sur L'Alimentation De Votre Chat by Prof Roger Wolter, Directeur du Laboratoire de Nutrition a l'Ecole Nationale Veterinaire de Maisons-Alfort (available in French only)