Nutrition

The Animal Welfare Act 2006, Section 9(2b) makes it a legal requirement that animal owners feed the right sort of diet in the right quantities. Most owners do not set out to break the law, but it is not always easy to know what the right diet is and vets estimate that more than half of owners overfeed.

Pet food is big business. More than a quarter of the population of the UK own at least one dog and/or a cat. In the US, it is more than half. The UK market was worth £2.7 billion in 2018, forecast to rise to £2.9 billion by the end of 2020. It is little wonder that a new dog food seems to come on the market almost every month nor that vast amounts are spent on marketing to appeal to owners, not always with regard to what is best for animals.

What Dogs Need

Understanding how dogs evolved and what dogs need is essential to providing the right diet. Dogs are not wolves and are not directly related to extant wolves. They self-domesticated between 15,000 and 30,000 years ago by scavenging from humans. Studies of those ancient dog population find that dogs ate what the humans ate, including diets high in starch and grains and low in meat. One of the reasons that dogs adapted so well to eating alongside humans is that they are also omnivores; humans and dogs do best when eating a diet that includes cooked meat and vegetable matter, although the balance and composition of the ideal diet varies between dog and human and between breeds of dog.

Although dog’s can cope better with pathogens than humans in that their gut is much shorter and there is less time for bacteria to multiply, they can become ill or spread pathogens to vulnerable animals and humans when fed an unsuitable raw diet. Bones cause mechanical injuries and cannot be crushed, digested and expelled safely. Wolves are able to do this because they have significantly more powerful jaws to crush bones and they eat game that is not reared at accelerated rates, causing brittle bones to shatter. Wolves eat the whole animal – hoof, hide and hair – which protects their guts if bone fragments are expelled. Dogs cannot do this.

A Dog’s Dinner – Commercial Pet Food

Until the 1960s, humans in western Europe mostly ate a much plainer, unprocessed diet and shared it with their dogs in the form of table scraps supplemented by fish heads and offal. Anyone who grew up with dogs in those years will probably not forget the smell of boiling tripe! Along with the dubious delights of the TV dinners in the 1960s, commercial pet food started to become widely available, although some canned food had been available since the 1930s. Pet dogs were mostly fed meat and a biscuit mixer and working dogs were (and still are) fed fallen stock flesh and mixer.

There were comparatively few dog food specialists and “treats” were limited. In the USA, Hills pet foods, a company that began as a rendering plant processing horse carcasses at the turn of the 20thC, was by the 1960s selling their first veterinary diet, originally developed to support a guide dog with kidney disease. This has spawned a plethora of “life stage” diets and diets to support various clinical conditions as well as introducing the concept of changing the diet as the dog ages.

Good quality complete diets provide an excellent basis for correct nutrition when fed in suitable quantities. They are processed at high heat to destroy pathogens, with oils, fats and nutrients added or re-introduced after drying. Because some damage occurs in the extrusion process which squeezes the food into the desired shape for cutting, a digest (hydrolysed protein) of liquid meat slurry is sprayed on and it is this that smells when the packet is opened. As with the remaining protein, it is important that this is sourced from a high quality meat and not made up of various animal derivatives.

Click here to see the Pet Manufacturer’s Association animated film of how pet food is manufactured.

Pet Food Labelling – What Dog Food Really Contains

Pet food manufacturers are under legal obligations to label food, but it is classified as animal feed in the same way as feed fed to livestock. Those that just put the legal minimum labelling on food can make it difficult to understand what the food comprises. Equally, it can be difficult to wade though the marketing claims to find what you are really offering your dog.

Legal guidelines state that “The prime purpose of a label is to facilitate the buying act of the purchaser by delivering clear, concise, accurate, true and honest information on the composition, characteristics and use of the product…The vocabulary used should be easily understandable by the average purchaser.”

The following listing is typical of a basic pet food label:
Crude protein
Crude fat content
Crude fibres
Crude ash.

How does that list enable you to know what that food actually contains or whether the balance is correct?

Protein

Protein can incorporate a multitude of sins. Only the best quality foods will have a reliable source of protein; the remainder use whatever is the cheapest available at the time; this can cause problems in dogs that are sensitive to dietary changes and most dogs can have a reaction to a sudden change. Many owners mistakenly look for a high protein content in a diet, regardless of the source, but that is not suitable for all dogs.

The ‘meat’ content is likely to be animal derivatives – the bits left over from processing human food. This can include highly nutritious offal and, with fish, can include the entire fish, usually cooked, dried and powdered. It is not allowed to contain hair, hoof, hide, feet, feathers or gut contents. It is not the same as mechanically recovered meat or the notorious ‘pink slime‘, both of which have been used in processed human foods. It is best to look for a named meat source. Beware also that there is a significant difference between fresh meat content and dried meat content. Fresh meat is the weight of the meat before processing, not the amount of the meat that is in the final product. Once the moisture content is removed to produce a dried food, the actual percentage of meat may be much lower.

Fats

Crude fat levels are for instance likely to be lower than actual fat levels and the source of the fats (added after processing in dry food) does not need to be stated. Some of these fats are essential fatty acids which are imporant for healthy brain and nerve function. Fats can also be oils. Again, it is best to opt for a named source such as linoleic acid (omega-6) which is at least 3% of the content, chicken, lamb or turkey fat or fish oil which is high in omega-3. Sunflower oil is also used, but tends not to be so palatable and is best when combined with a named animal fat. The crude percentages refer to the dry weight of the food; actual levels may be higher as dry food may contain up to 14% moisture. Caution needs to be taken to understand the actual fat content for instance with a pet on a diet or for young animals.

Fibre

Crude fibre refers to complex carbohydrates that resist enzymatic digestion in the small intestine. Common sources include rice hulls, corn and corn by-products, soybean hulls, beet pulp, dried potato product, cellulose, bran, peanut hulls and pectin. Fibre is an important element of the dog (and human) diet, helping to improve colon health, weight management (high fibre diets that help your dog to feel full without adding lots of calories). When fermented into fatty acids by bacteria in the intestine, fibre helps to prevent the overgrowth of harmful bacteria. Diabetic dogs that eat a high fibre diet may experience less fluctuation in blood sugar levels. Fibre can also prevent anal sac impaction, common in small dogs. As with other ingredients, the source of the fibre is important. Poorer quality foods can be up to 80% grain and manufacturers will source the cheapest available grain so content will not be consistent. Look for a named cereal such as rice which is highly digestible, or a food that includes vegetables.

Ash

Crude ash sounds as if it comprises embers from a fire added as a filler, but it is in fact the mineral content of the food and can include calcium, phosphorus, zinc, iron, sodium, potassium, chloride, copper, manganese, selenium and iodine and other minerals which are essential to a balanced diet when present in the right amounts. Ash composition may be higher in high protein foods so it would be more beneficial for manufacturers to state levels of actual minerals, especially calcium, which should not be over-fed to growing dogs.

Additives – and Added Claims

Then there are additives. Some are beneficial, some less so. It is not obligatory to state details of additives unless they have a maximum legal level for the species for which the food is being sold but many companies are promoting various additives as being beneficial.

Some additives are preservatives. This includes anti-oxidants which can be from ‘natural’ tocopherols, including vitamin E, or synthetics such as Ethoxyquin (E324), Butylatedhydroyanilose (also labelled as BHA or E320) and Butylatedhydroyutoluen (also labelled as BHT or E321). This enables the food to have a long shelf-life and stops the fats from becoming rancid once opened. Vitamins are added after heat processing which destroys any that were originally present. They decay over time though, so it is important to store food correctly and use it before its ‘use by’ date. Other additives include preservatives that inhibit deterioration, emulsifiers that enable some ingredients to be mixed, stabilisers, thickeners and gelling agents, binders, anti-caking agents, acidity regulators and substances that can suppress or reduce moulds (mycotoxins). Again, they can be ‘natural’ substances or synthetic chemicals and are the price paid for the convenience of food that has a reasonable shelf life.

Beneficial claims have been made for the prebiotics Fructooligosaccharides (FOS) and Mannan oligosaccarides (MOS). They occur naturally in plants such as onion, chicory, garlic, asparagus, banana and artichoke and are promoted as being beneficial to the digestive system. However, studies undertaken in 2019 found that “…there is no evidence that dietary FOS maintains or improves visible health and extends longevity in dogs“ and that “Corn-based dry foods are in themselves high in mannose, possibly making MOS addition redundant. But most importantly, there is no research evidence that extra dietary MOS perceptibly promotes health and longevity in dogs…the same time, the bad clostridia bacteria are not depressed. Using the bacterial profile as indicator, MOS may not promote gut health in dogs. “ 

Similar claims have been made for added digestive enzymes. A 2016 study concluded “The available research data do not support efficacy and practical use of adding digestive enzymes to the diet of healthy dogs.”

So-called “super fruits” such as blueberries and pomegranate have been promoted as being healthy for humans and are now being included and promoted in dog food. As a 2016 study notes “The term superfruit is not regulated and can be applied as a marketing tool to any fruit…Super fruit is lauded for being packed with vitamins. As a constituent of complete and balanced pet food this is not relevant…Claimed health benefits comprise supporting immune action, urinary tract, memory function and cardiovascular system. These assertions cannot be substantiated by research data in dogs.” 

 

Food colourings are completely unnecessary to nutrition. They are added to appeal to the human buying the food and are not visible to the red-green colour blind dog anyway. If the food that you are feeding glows brightly with vivid colours, ask yourself if you would want to eat all that food colouring and then bin it. Permitted food colourings include tartrazine,
sunset yellow FCF and patent blue. The Food Standards Agency which governs human food has suggested that tartrazine and sunset yellow may be implicated in hyperactivity in children. The European Food Safety Agency states of patent blue “It would be prudent to treat Patent Blue V as an irritant and a skin sensitiser and as toxic by inhalation”.

There is a paucity of studies on dogs with regard to the effects of food colourings, but surely it is not worth the risk?

If you feed wet food that makes your hands sticky, the chances are that it will contain a lot of sugar. Sugars are not limited to wet foods however. Sugar is added as part of the processing and to ‘aid’ palatability. Dogs, like humans, are attracted to sweet tastes. Dog food also often contains a high proportion of salt. Although salt is not implicated in problems such as high blood pressure (hypertension) in dogs as it is in humans, the combination of high sugar, high salt and high carbohydrate content makes food highly addictive. As with humans, dogs fed on diets high in all of these ingredients will undergo physiological changes that make them crave more and that override their natural feeling of being full. A recent study concluded that 26% of dogs surveyed from photographs taken at Crufts were overweight, so the problem is not just endemic in pets.

This website has a list of pet food ingredients with definitions.

What Is Natural?

There has been something of a reaction to processed food of all kinds, in parallel with concerns about human food. Some owners, not to mention canny pet food manufacturers, therefore gravitate towards a supposedly ‘natural’ diet. But what is ‘natural’ for a domesticated dog? Dogs evolved as scavengers. Feral dogs scavenge and may eat game and rodents. In addition to scavenging processed foods from human waste dumps, feral dogs will, like wolves, eat the whole animal when they catch prey.

One food, labelled as ‘natural’ in fact contains a high proportion of barley and oats which may be totally unsuitable for some dogs. Another is marketed with a drawing of a farmhouse, complete with Labrador by the Aga and a trug of ‘ingredients’ supposedly awaiting inclusion in the ‘natural’ diet. The problem? The trug includes a large bunch of grapes – toxic for dogs! Legally, the term ‘natural’ includes anything “derived from plant, animal, micro-organism or minerals to which nothing has been added” – just about everything then. However, it is permitted to continue to label a food as natural if processing of components has included “freezing, concentration, extraction, drying, pasteurisation or smoking as far as they maintain the natural composition… Microbiological and enzymatic processes or hydrolysis” as long as the processes have not involved the use of chemicals.

There has been a fad for “grain-free” diets that accompanied the fad for gluten-free diets in humans. Dogs evolved to eat starches such as grain thousands of years ago as they lived alongside man and scavenged or were fed their scraps. Studies from Stone Age people and their gos showed that the dogs were eating mostly grain-based foods as did the humans. That said, not all dogs can tolerate high-starch diets as they have differing numbers of starch receptors. Generally speaking, northern breeds have fewer starch receptors than dogs that evolved in the Fertile Crescent.

What Is Beneficial?

In an attempt to justify processing and charge premium prices, some dog food manufacturers promote chelation of ingredients. Chelated trace elements consist of a ring of atoms with the trace element as link which form a specific class of organically bound trace elements. They have been claimed to be superior to inorganic sources that contain no or only one carbon atom. It is often stated that chelates are taken up by intestinal cells more efficiently, have prominent regulatory and catalytic activity in the body’s metabolism and support the immune system. Added “organic zinc” has been claimed to promote a so ft and shiny coat, for instance. A 2016 study found that “Little is known about the nature of degradation products of intactly absorbed chelates. Research data in the public domain cannot substantiate chelate-mediated health advantages in dogs. All in all, organic trace elements do not appear to be superior to inorganic sources.”

So-called “hypoallergenic” diets purport to be suitable for dogs with food intolerances and allergies. There is no legal definition of the term; some companies claim that all of their food is hypoallergenic and others promote specific products.

Marketing pet food is big business. According to the Pet Food Manufacturers’ Association, the UK pet food market was valued at over £3.2 billion in 2021, dog food amounting to £1.5 billion. Human and pet food marketers are very astute and, without actually infringing the law by making claims that could be cited as being misleading, nevertheless manage at the very least to obfuscate. 9 out of 10 owners don’t understand dog food promotions maybe? The key is in the definition on the packet. Take the following example of the fictional Doggo dog food:

Doggo All Chicken: must contain 100% chicken (animal derivative, remember, not ‘muscle meat’) with no other ingredients except permitted additives, nutrient supplements and water for processing

Doggo Chicken Dinner: sounds the same but may legally contain just 26% chicken

Doggo Rich in Chicken: may legally contain just 14% chicken

Doggo with Chicken: may legally contain just 4% chicken

Doggo Chicken Flavour: doesn’t have to contain any chicken at all as long as the dog perceives the taste to be chicken!

So, caveat emptor et cavete canis cibum!

BARF Diet

BARF is an acronym for Bones and Raw Food or Biologically Appropriate Raw Food (they can’t decide which).

In an attempt to feed their dog a ‘natural’ diet and as a reaction to highly processed commercial foods, some owners are proponents of feeding raw food and bones. The BARF diet web site states “we believe all dogs should have the right to be fed what they love best!” (My dog would probably chose something decomposing behind a waste bin).

The quotations included below are from a scientific study published by Daniel Schlesinger and Daniel Joffe available in the online edition of the Canadian Veterinary Journal.

BARF repeat in the first two paragraphs of their exposition that it is a diet “natural to their environment as if they were living in the wild”. But they are talking about domestic dogs: the whole point is that do not live “in the wild”. They have adapted through natural selection and selective breeding over at least 12,000 years to not living in the wild, although some are of course feral. Dogs scavenge from humans and most eat a starch-rich diet, feral and companions.

Schlesinger and Joffe remind us that there are no published, scientifically valid studies of nutritional benefit of raw meat feeding to dogs. “The only available published information on feeding raw meats to a number of dogs and cats that could be interpreted as remotely positive is a survey study on feeding practices in the United States and Australia”. In this study, only 3% of owners were feeding an exclusively raw diet and the assessment of the pets’ health was based on the owners’ perception.

BARF recommendations include a range of stoned fruit and citrus fruits and apples (apple pips are toxic and stones can be as well as causing mechanical damage if ingested). Lemon, limes and grapefruit are also toxic as is the pith and peel of all citrus fruits. They state that garlic is “not allowed”. Garlic, unlike other members of the allium family, can be fed in therapeutic amounts to great effect, bought in tablet form to ensure a controlled dose as well as being used as a spray to deter ectoparasites. They suggest adding honey, cottage cheese, yoghurt, raw eggs, flax seed oil, brewers’ yeast, kelp tablets, vitamin C (extra strong) and cod liver oil.

Do you really want to be mixing that many ingredients for every meal that your dog eats? What if you are ill or need to leave your dog with someone else. Will they be expected to do this too? Can you control the amounts and ensure that all the trace elements that your dog requires will be present?

Schlesinger and Joffe tell us that “Nutritional osteodystrophy was reported in 2 litters of 6-week-old large breed puppies fed a bones and raw food (BARF) diet from about 3 weeks of age. Nutritional secondary hyperparathyroidism has also been reported in a litter of German shepherd puppies fed a diet of 80% rice with 20% raw meat. The diet contained excessive amounts of phosphorus. Not all puppies fed the diet experienced problems, suggesting individual or genetic susceptibility. A nutritional analysis of 5 raw food diets (2 commercially produced and 3 home-made) found low calcium and phosphorus in 3 of the 5 diets. Two commercial diets were high in vitamin D. Two of the diets were deficient in potassium, magnesium and zinc.”

The bulk of the BARF diet comprises raw meat and bones. “DO NOT COOK THE MEAT!” they shout on their web site because they feel that cooking destroys essential enzymes. The Schlesinger and Joffe paper cites the fact that proponents of raw feeding have themselves cited a single scientific article “supporting their contention that digestive enzymes in fresh food enhance biological availability and that heating depletes these enzymes and therefore the nutritional quality of the ingested food”. This was a study based on human digestion; dogs do not possess the same gut bacteria or digestive enzymes as humans. Furthermore “the authors state that the role of enzyme synergy has not been studied in sufficient detail to predict its biological significance”. The Food Standards Agency in the UK published results on campylobacter contamination in chickens:
15% of chickens tested positive for campylobacter within the highest band of contamination
76% of chickens tested positive for the presence of campylobacter
0.3% of packaging tested positive at the highest band of contamination
6% of packaging tested positive for the presence of campylobacter.
The contamination has been of so much concern that many retailers now wrap their chickens for cooking in bags to prevent the handling of raw birds.

Whether cooking destroys enzymes or not, it certainly will not have destroyed parasites (especially tapeworm) or bacteria such as salmonella (also prevalent in raw eggs)¹, e.coli, giardia, listeria and campylobacter. In the Canadian study, “Almost 6% of the raw food diets were positive for Salmonella, while none of the conventional diets were positive. Escherichia coli were isolated from all types of diets. It was found in almost 50% of the raw food diets but in only 8/24 (33%) dry and 2/24 (8%) canned diets. There were no significant associations between the type of raw meat and the agents isolated…80% of raw chicken diets were culture positive for Salmonella serovars, while none of the commercial dry foods were positive.”

Dogs fed on diets that have salmonella and e.coli will be shedding bacteria in their faeces. “Thirty percent of the stool samples of the raw chicken eaters were also positive; the commercial diet consumers’ stools were negative”. More worringly, the spread of anti-biotic resistance is implicated for humans and pets. “A study analysing 166 commercially available raw food samples, purchased randomly from local pet stores in 3 Canadian cities found a prevalence of 21% for Salmonella, with chicken being an ingredient in 67% of the positive diets. Eighteen serovars were observed with resistance present to 12/16 antibiotics tested”.

There is also a concern that owners handling raw foods will transfer bacteria to other humans with whom they are in contact.”An outbreak of disease due to multi-drug resistant Salmonella Typhimurium in 4 animal facilities has been reported. Illness occurred in employees, clients and animals that were present in 3 different companion animal facilities and 1 animal shelter. Eighteen humans and 36 animals were faecal culture positive for Salmonella. Some of the animals died. Equally disturbing was that some animals in the facilities and in clients’/employees’ homes cultured positive but were asymptomatic. Those affected clinically included veterinary staff, pet owners, children and other pets.” So, you or your pet might not show any signs of infection but you could be spreading lethal bacteria to everyone around you and their pets.

Even the most clinical of home hygiene regimes may not be sufficient and can you guarantee that you will maintain them 100% of the time? “As there appears to be strong evidence that raw food can contain Salmonella, it is vitally important, if feeding a raw meat diet to a pet, that hygiene of the food preparation area and the feeding bowls be diligently maintained. This may, however, be difficult to achieve. A recent study found that standard methods of cleaning and disinfecting food bowls were minimally effective at eliminating Salmonella. This included soaking with bleach and cleaning in a dishwasher.”

Bones can also harbour harmful bacteria. There is controversy over whether dogs should be fed bones at all and, certainly, when they are, the advice is that they should never be fed cooked. However, the bones fed in the BARF diet come from commercially farmed animals, especially chickens. These animals are reared to mature quickly and often suffer from osteoporosis. This means that even raw bones will be comparatively brittle and liable to splinter easily. Shards of bone can cause a huge amount of pain and damage to a dog. The Royal Dick Veterinary College in Ediburgh has produced an advice sheet on the BARF diet which includes the following recommendation: “If you feed bones, either raw or cooked, that can be ingested by your dog, you are running the risk of oesophageal or gastrointestinal obstructions. It may be possible to chop or grind the bone up small enough (e.g. less than 0.5 cm) so that they are less likely to get stuck. Alternatively, consider consulting a veterinary nutritionist to determine the amount of calcium (and likely other nutrients) to add to his diet and skip the bones.”

A blog from the online version of The Veterinary Record cites a case study of a four-year-old golden retriever that had been vomiting intermittently and had been lethargic for a few days. The owners fed a diet comprising chicken bones and raw food, boiled potatoes and pasta. The dog had not ingested a foreign body. A loop of the dog’s intestine had twisted (segmental small intestinal volvulus), a condition that is often fatal. However, in this case, the dog recovered although the vet removed a small section of the intestine. This was found to contain several chicken bones. The vet concluded that “…it demonstrates that intestinal obstruction with secondary volvulus can occur due to dietary obstruction when a dog is fed a BARF diet.”

Now there may be howls of protest from owners whose dogs have not suffered any notable ill effects but I for one would not want to play Russian roulette will my dog’s digestion or perhaps his life.

There are many choices to be made when deciding on the best diet for your dog, but in the end, current, independent evidence on the BARF diet seems to be unequivocal:

“Clearly, there is some compelling evidence suggesting that raw food diets may be a theoretical risk nutritionally. In addition, raw food poses a substantial risk of infectious disease to the pet, the pet’s environment and the humans in the household. What is lacking, however, is level 1 evidence from randomized controlled trials or strong level 2 evidence from large cohort studies to evaluate risks or benefits of raw meat diets in pets. There is, though, sufficient evidence available that veterinarians should feel obligated to discuss the human health implications of a client’s decision to use a raw meat-based food for their pet.”

Footnotes
1 Latest research from the Food Standards Agency (FSA) suggests that salmonella levels have dropped markedly in their Lion Code scheme eggs. if you must feed raw or lightly cooked eggs, look for eggs with the lion mark.

Common Canine Toxins

There are many commonly encountered substances that are toxic for dogs and care should always be taken to monitor the environment, supervise your dog where necessary and take especial care with puppies, young dogs and dogs that are very food-orientated.
The following are some of the most common reasons for dogs being poisoned…Read more