RFVS Conference 2021 - Dr Rebecca Brown

The debate really is not whether to formulate versus not formulate. With zero formulation, we could just be tipping any old thing into our pets’ bowls: chocolate fish, old socks, cardboard. The debate is really about how much we formulate.

There is a spectrum of formulation including but not limited to: Live prey ⇒ dead prey ⇒ deconstructed approximated prey-based diet: raw meat, bones, organs and tripe (that’s us) ⇒ prey modeldiets ⇒ raw with multivit supplements (+/- AAFCO) ⇒ convenience (AAFCO) raw (eg K9 Natural). Some level of formulation is absolutely necessary of course (to avoid the inevitable poor outcomes of a sock-based diet). But how much is necessary, how much is useful, and does it really matter?

The aim of a raw diet is to provide palatable, satiating, highly-digestible, nutrient-dense, species-appropriate food that fulfills a dog or cat’s nutritional needs. In our practice, this is a diet of raw meat, bones, organs and tripe from a variety of prey sources. Raw Essentials does not formulate from ingredients. Rather, it is just species-appropriate food.

This talk will spend more time exploring how we don’t formulate than how we do formulate. This is because our approach to formulation is very simple, and does not require a great deal of explanation.

Raw Essentials was set up by Dr Lyn Thomson over 14 years ago. What a gift to New Zealand! Though vets were initially somewhat reserved, clients and their pets were hungry for it. We provide high quality raw food from short, transparent, sustainable supply chains, along with an abundance of advice and support through our 17 national stores and online.

Using the FORMULA that NATURE created we emulate a prey meal as closely as possible, chopping and mincing prey into meal options for cats and dogs. We keep it simple - meat, bone, organs and tripe from a variety of prey sources, in approximate prey proportions.

When a new client walks in the door of a Raw Essentials store, they’ll be met by one of our nutrition advisors. We want to know everything about the pet, including any past or current health concerns, medications, digestion history, activity levels, tendency to anxiety etc etc. All this is so we can best advise an appropriate transition plan and maintenance diet.

Our transition plans may involve a simple overnight switch to a raw diet, or a more nuanced transition via a Gut Healing Protocol (GHP). A GHP starts with easily digestible, poached meats; and then sequentially introduces the various components of a raw diet, all the while closely monitoring the response of the pet. Cases which are medicated, on prescription foods or under direct veterinary care are referred to our veterinary support team who liaise with the primary veterinarian to create a plan acceptable to all. Raw Essentials does not offer conventional veterinary services. We do our utmost for pets with healthconcerns, through optimising nutrition and gut health

We move around 27 tonnes of frozen food every week, enough to feed 20,000 small dogs. 40% of our frozen food is wild prey or contains a wild component; the rest is largely free ranging, from the human food chain.

We have a range of minced products (which include meat, bone, organs and tripe). These make it easy and convenient to feed a variety of prey sources. We have various meal-sized whole meaty bones, meat fillets, tripe and some dried products for chewing and recreation.

We encourage feeding appropriately sized raw meaty bones where possible. Chewing on raw meaty bones increases satiety, improves dental health and is obviously downright enjoyable. Fagan et al 1 illustrated this in zoo animals - the hassle factor is highly beneficial to carnivores. Whole bones are not suitable for all pets. Situations that provoke caution include brachycephalic breeds, dental disease, greedy pets, heavy pregnancy and gastric acidity challenges due to aging, medications, disease, carbohydrates and anxiety.

Our mission is to help people feed their pets a raw diet that is safe, beneficial, sustainable and convenient.

1) AAFCO - WE DON’T USE IT

Let’s look at diets on the more formulated end of the spectrum: Raw diets constructed to meet AAFCO requirements.

There are obvious advantages to these:

• They are convenient because they do not require planning - each meal is ‘complete and balanced.’

• Given that nutritional adequacy is one of the most common concerns that veterinarians have about raw diets, an AAFCO compliant diet will provide owners and veterinarians with a level of comfort.

AAFCO defines pet food ingredients, and specifies the minimum and maximum acceptable levels of a range of nutrients in processed cat and dog food. AAFCO may be the best option we currently have for processed foods.

While some AAFCO compliant raw diets are no doubt really good - is this because of their AAFCO compliance, or because they are species-appropriate diets utilising high quality ingredients?

We do not use AAFCO, because we don’t feel that it is the best yardstick by which to measure our diet. Here are our reasons for thinking this way:

a) AAFCO utilises reductionist nutrition

“Nothing in Biology Makes Sense Except in the Light of Evolution.”2 Theodosius Dobzhansky Gyorgy Scrinis3 introduced the idea of reductionist nutritionism: over the last hundred years scientists have identified, quantified and qualified individual nutrients; resulting in public health messages about what constitutes ‘good’ and ‘bad’ nutrition. Despite this growing body of knowledge, chronic disease is increasing rapidly in both people and their pets.

Nutrition science is missing the mark. Reductionism fails to understand the true complexity of real food:

“attempting to mimic food sources using single constituents such as isolated proteins, vitamins, and minerals is challenging and arguably underestimates the complexity of the food source it is meant to mimic..since foods contain thousands of constituents that can synergistically impact human metabolism, consuming isolated nutrients or fortified foods often do not confer similar benefits when compared to ingesting nutrients as part of their whole-food matrix.4

Raw Essentials emerged from the recognition that, if we leave the narrow confines of reductionism, and widen our perspective so that our viewpointincludes evolutionary biology and nutritional ecology, it becomes apparent that what makes sense is minimally-processed, unadulterated, species-appropriate food - as nature intended it.

Identifying a single nutrient requirement in isolation does not tell us how much of that nutrient an animal needs in real life. The nutrient does not exist in a vacuum. Its availability and action will be affected by multiple factors, including:

● The form of the nutrient: Is it presented in a whole food form, or as an inorganic supplement?

● The interaction of the nutrient with other nutrients: For example, high starch foods such as grains impair the absorption of minerals such as zinc.

● The condition of the animal: An animal with chronic health issues, or on medication will absorb and utilise nutrients quite differently to a healthy, unmedicated animal.

Some examples of factors affecting nutrient absorption include:

● Previous iodine5 intake history affects the response of an individual cat or dog’s thyroid gland to future dietary intakes.

● “Reductions in the secretion of hydrochloric acid, gastric acid, and/or intrinsic factor, together with alterations in the permeability of the

intestinal mucosa, are all examples of intestinal factors that can markedly influence the absorption of certain nutrients, but that are often ignored when setting dietary requirements.”6 Omeprazole is a commonly prescribed drug in dogs which reduces acid secretions.

● "Folates are produced by bacteria in the gut and are absorbed, but the contribution has not been quantified...the type of diet will affect the amount absorbed...The folic acid needs of dogs given diets based on natural constituents and not containing bacteriostatic agents [antibiotics, preservatives] may be partially met by microbial synthesis in the intestine...diets that are inadequate in choline... may increase requirements for folic acid."7

● "The quantity of vitamin E required in the diet depends on the rate of production of free radicals, the PUFA composition of membranes (a function of the diet), and other dietary compounds such as selenium"7

b) AAFCO is for processed diets, not raw

AAFCO nutrient recommendations are based on the work of the National Research Council (NRC). The NRC book7 contains nutrient requirement tables for cats and dogs, and a description of the available nutrition science behind the tables. The scientific papers relied upon in the book almost always examine processed diets, and thus the tables are mostly pertinent to the needs of a dog or cat on a processed diet. There are many ways in which nutrient requirements of cats and dogs on a processed diet differ from those on a whole food diet. The authors of the book point this out multiple times as a caveat.

c) AAFCO requirements are a bit of a guess

Unfortunately, there is not a great deal of good nutrition science for either raw, or processed-fed pets. Most studies are small, and poorly designed. Wading through the NRC book you will find that the authors repeatedly warn us that the established requirements are a best guess based on a paucity of science. All too often people interpret the numbers in the NRC as ‘settled science,’ without considering the qualitative statements explaining how tenuous the science actually is.

So in the absence of reliable data from large controlled studies we are left mwith a combination of supportive data, evolutionary logic (one of the most important questions in science: “does this make sense?”), and clinical experience to decide how best to feed our pets. Clinical experience tells us that despite AAFCO compliant diets being the current dominant pet food: obesity, heart disease, skin disorders, diabetes, dental disease, renal disease and cancer are common occurrences. If our grasp of nutrition science wasreally good, vets and GPs would not be nearly so busy.

Take iodine as an example of the uncertainties. Although AAFCO generally follows NRC guidelines, they differ significantly in their iodine recommendations. The NRC states that:

“To our knowledge, however, there have been no detailed studies with cats to determine the range of daily iodine intake that is consistent with normal thyroid structure and function, particularly mstudies of iodine intake conducted over a long period of time...Untilmore data are accumulated concerning a possible relationship between levels of iodine intake and altered structure or function of the thyroid, it seems reasonable to recommend that pet food manufacturers should adjust the levels of iodine in their products to lie within the broad, albeit at present ill-defined, limits that have been recommended.”7

Assessing the requirement for iodine is complicated. The NRC’s figures have been called into question:

“The recommended iodine intake across species appears to follow metabolic scaling for body weight (FIGURE 2). The recommended daily allowances for dogs and cats suggested by the National Research Council (NRC) in 2006 are in excess of NRC recommendations for other species, current AAFCO recommendations in cats, and earlier recommendations for dogs and cats based on metabolic body weight. The dietary iodine requirement in cats has recently been suggested to be closer to 0.46 ppm than to the 1.3 ppm reported by the NRC.”5

In 1970, recommendations fitted a metabolic scaling line along with other species. Today, cats and dogs are outliers.

The studies supporting the NRC iodine requirements had several flaws. Wedekind et al (2010)8 analysed the three studies and pointed out their weaknesses:

"The new NRC I [iodine] recommended allowances for the cat were based on three studies (Scott et al., 1961; Smith, 1996; Ranz et al., 2002) all of which failed to meet key criteria necessary for defining nutrient requirements. The Scott et al. (1961) study was never intended to be used as a requirement study; the diet used was an all meat diet (beef or sheep hearts) deficient in Ca, vitamin A and I and an imbalanced Ca:P ratio." 8

d) AAFCO is pretty unreliable in the real world

Consistency is incredibly challenging in the real world - diets which have been formulated to meet AAFCO often fail to actually meet AAFCO, rendering the formulation pretty redundant. To the best of our knowledge, AAFCO-compliant raw diets have not yet been included in independent studies checking compliance, but non-raw diets have certainly performed poorly.

The Scientific Reports journal (2017) published a paper9 in which the authors analysed 177 widely available dog and cat foods to see if they complied with FEDIAF (the European version of AAFCO) guidelines for completeness. They discovered that only 8% of wet foods and 39% of dry foods did. Pets were shown to be at risk from copper and selenium toxicity due to the high levels in some foods. The ratio of calcium to phosphorus (vital for proper bone growth) was wildly out in many products. 40% of the foods in the study had excessive ash levels, which is associated with renal disease. The authors suggested a link between the non-compliant foods and disease:

"A majority were non-compliant according to current European recommendations (FEDIAF, 2013). Many had either insufficient, excessive or an inappropriate balance of minerals which, if fed exclusively for a long period of time, could underpin a host of clinical diseases in dogs and cats including skeletal, neurological, or dermatological disease. Furthermore, foods with relatively high levels of fish or fish derivatives (i.e. ≥ 14%) also had high levels of undesirable metal elements such as arsenic, which bioaccumulate in internal organs and may contribute toward a plethora of subclinical disease" 9

Issues included:

● High fish (derivatives, but not oil) content foods had high arsenic and mercury:
"Given that chronic arsenic intake in human epidemiological studies is associated with albuminuria, proteinuria and increased mortality from kidney disease then one must question why a high proportion of these diets are fed to domestic cats, whom are prone to chronic kidney disease."9

● "40% (71 of 177) of foods analysed in our study had ≥10% ash on a dry matter basis, nine with ash ≥14%. Higher ash intake is associated with CKD in cats."9

● Minerals were often far too high, or too low:

• Copper - some had more than 2x the maximum (impact on zinc and iron), some had less than 1⁄2 the minimum.
• High selenium in 76% of wet food (7 products had more than 3 times the maximum)
• Ca:P ratio wildly out in many products
• 32 products had excess calcium
• In a New Zealand study10 , Hendricks et al (1997) analysed 29 cat foods (ranging from budget to super premium) to see if their label claims of meeting AAFCO standards were true. 60% of the budget, 18% of the premium, and 43% of super premium cat foods failed to meet their stated AAFCO standards.

“The present study provides hitherto unavailable information on the nutrient composition of soft-moist cat foods sold in New Zealand, and indicates that a number of soft-moist cat foods cannot claim to be formulated to meet the nutrient profile of the Association of American Feed Control Officials.”10

A study11 in the Journal of the American Veterinary Association (2014) found that 13.3% of canned cat foods from 45 different brands - all claiming to meet AAFCO standards - were below AAFCO for thiamine (and 15.6% were below NRC for thiamine), which has very serious implications for feline health. Four of these foods were manufactured in New Zealand.

The Journal of Animal Physiology and Animal Nutrition (2013) published a paper 12 in which they analysed 12 hypoallergenic diets. These expensive diets are supposed to be free from allergenic proteins in order to relieve itching in pets. 10 of the 12 diets were contaminated with protein allergens not declared on the label. Another paper13 in the same journal found that all four of the allergy diets they studied were contaminated.

The Australian Veterinary Journal published a paper 14 (2016) which analysed 10 wet and 10 dry ‘complete and balanced’ commercial cat foods, and compared the results with the labelling on the packages, and with established dietary requirements (AFFCO and NRC) for cats. The nutrient compositions and guaranteed analyses listed on the labels failed to match the chemical analyses carried out in the study. Deficiencies and excesses of various nutrients were found in nearly all the samples, many of which were identified as potentially harmful to cats ingesting the diets.

“The various nutrient deficiencies and excesses observed in a majority of the foods in this study highlight a serious issue in the nutritional composition of commercial cat foods in Australia. Both the nutrient composition and feeding guidelines require extensive review to ensure the adult cat’s unique dietary requirements are being met.”14

In a 2004 study 15 from the Archives of Veterinary Medicine, 33 brands of dry dog food were analysed to see if they met AAFCO standards. Seven foods had an incorrect calcium:phosphorus ratio. There were inadequacies for potassium (13 foods), zinc (7), iodine (12) and selenium (1). Only 12% of the foods met the minimum requirements for protein, fats and minerals.

a) Synthetic micronutrients

Synthetic micronutrients do not behave in the same manner as their food-origin counterparts.

Two human nutrition science studies 16 were pivotal in drawing attention to the difference between whole food and synthetic nutrients. Epidemiological (observational) studies identified a link between diets high in carotenoids (lots of fruit and vegetables), and high levels of serum ß-carotene with lower cancer incidence (particularly lung cancer). The correlation was particularly strong in lung cancer patients with a history of smoking. These findings led to the initiation of large controlled supplementation trials. The results were rather shocking:

● The Alpha Tocopherol, Beta-carotene Cancer Prevention Trial (ATBC) revealed an increase in lung cancer risk in the treatment group - smokers who took the ß-carotene supplements.

● The ß-carotene and Retinol Efficiency Trial (CARET) led to an increase in cancer among smokers and asbestos workers.

Both trials were halted before completion due to the increased death rates in the treatment groups.

More recently, evidence in pet nutrition has pointed to similar issues.

Renal (kidney) disease is common in dogs and cats. Survival time in patients with renal disease has been shown to improve when dietary phosphorus is reduced. The implication of this is that too much phosphorus is damaging to the kidneys. This led to the development of prescription renal diets (low in protein and phosphorus).

A recent paper 17 in the British Journal of Nutrition (2019) made an important finding regarding the difference between whole food and supplementary phosphorus. The authors pointed out that “Phosphorus is present in diets as naturally occurring P from raw materials or added as an inorganic salt”17 but that little is known about how these two forms of phosphorus are absorbed in cats after ingestion. Using the data from several studies, the authors concluded that supplementary phosphorus led to an increase of phosphorus levels in the plasma, however phosphorus from whole food did not. So it is possible that the ubiquitous incidence of renal disease in pet cats is, at least in part, due to the presence of supplementary phosphorus which has been added to their processed diets in order to achieve AAFCO requirements.

Another paper 18 in the British Journal of Nutrition (2018) adds weight to this idea. Key points in the paper are as follows:

● “Renal disease has a high incidence in cats, and some evidence implicates dietary P as well...The bioavailability of dietary P is not only influenced by the P content of the diet, but the ratio of Ca:P and source of P have also been demonstrated to play important roles in absorption.”18

● Whole food versus supplementary forms of phosphorus affect plasma and urine levels of phosphorus differently: “Phosphates are widely used in commercial human and pet food manufacturing, where they serve a number of processing functions and as a source of required dietary P. Such P salts easily disassociate, solubilise and are readily absorbed in the intestinal tract; hence, P absorption can be greatly influenced by the chemical form ingested, with both circulating P concentration and urinary P excretion influenced by differences in dietary P availability.” 18

● Supplementary phosphorus is considerably more bioavailable than whole food phosphorus, which suggests there is a greater risk for excessive phosphorus absorption on a processed diet: “Evidence suggests that over 90% of inorganic P may be bioavailable, compared with between 40 and 60% for naturally occurring sources.”18

● Supplementary phosphorus (compared to whole food phosphorus) may actually be harming the kidneys of healthy cats: “Our findings therefore support other reports indicating that diets including high levels of P from inorganic salts may have adverse effects on renal health in healthy cats.”18

Zinc also acts differently depending on the source. Karen et al (1998) 19 found that organic zinc sources were more bioavailable compared to inorganic zinc (such as the zinc oxide form used in Hills products). They explained that:

“organic Zn sources resulted in greater Zn retention, higher concentrations of Zn in hair and greater hair growth compared with ZnO.”19

No doubt there is still much to learn about the difference between synthetic and whole food nutrients. What little we know so far is not yet accountedfor in AAFCO recommendations.

In many (maybe most) cases micronutrients present in whole foods are absorbed and utilised in a way that makes deficiency and excess less likely.

“Clinicians should also highlight the many advantages of obtaining vitamins and minerals from food instead of from supplements. Micronutrients in food are typically better absorbed by the body and are associated with fewer potential adverse effects.”20

b) Additives

A range of additives can be used to make food safe, stable, palatable, and convenient to handle and store. Long shelf lives are convenient for pet owners. But many of the additives used are controversial in terms of their effects on health. An article21 in Autoimmunity Reviews (2015) postulated mechanisms by which food additives contribute to the rise in prevalence of autoimmune conditions.

A paper22 in the Journal of Small Animal Practice (2021) reviewed the most common pet food additives, and found a number of concerning effects, for example: reductions in protein digestibility, potential carcinogenesis, haematological abnormalities, reduction in micronutrient availability, inflammation, and genotoxicity.

Our raw diet contains no additives. It is inherently palatable. Safety and stability is maintained through proper storage and shorter shelf life.

The prey model is about numbers: 80:10:10 (80% meat, 10% bone, 10% organs). These numbers have no scientific basis, because they will vary depending on the prey. Our own dissection studies at Raw Essentials revealed a rabbit (ideal prey for cats and dogs) to be about 25% bone. There will also be variation in what bits of the prey are eaten - a pet may eat whole prey, but more often they will be selective regarding the parts that they favour.

Whilst a quantitative approach can offer us valuable guidance, - it is incredibly difficult to apply in real life. Numbers simply do not behave once they are unleashed in the complex matrix of nutrient, gene, microbiota, environment and lifestyle interactions. Underestimating this can result in a false sense of security. Equally, striving to achieve a rigid adherence to numbers can create a great deal of stress.

We keep things as simple as possible. We aim to cover all the bases by offering a variety of nutrient-dense food. We allow the pet some room to follow their natural instincts. And we constantly ask ourselves: “Is this working? Are our pets thriving?” Feedback from the animal is vitally important - energy levels, demeanour, appetite, digestion, coat and body condition, bloodwork - all key indicators of health and vitality. (Afterall, this is what the short AAFCO trials are based on).

a) Carbohydrates

The rise in obesity in pets23 is concerning, and the role of carbohydrates is increasingly well understood. Fat cells produce inflammatory cytokines and contribute to a range of disease states.

Nutritional ecologist, Professor David Raubenheimer24, demonstrated that dogs, cats and humans eat to satisfy their protein requirements. By diluting the protein content of a diet with carbohydrates, the dog or cat will be driven to eat their way through the extra carbohydrate in order to get enough protein.

Dogs and cats have no established requirement for carbohydrates. They are expendable - the one macronutrient that we can all survive without. Additionally, the fibre25 component of carbohydrates reduces the absorption of essential nutrients.

We refer to a raw diet supplemented with carbohydrates as ‘mixed feeding.’ Mixed feeding may impact gastric acidity, thus impeding protein digestion and raising the risk of food-bourne illness. (ref 26 , ref 27 , ref 28 , ref 29 , ref 30)

b) Vegetables

Feeding vegetables to pets is popular. To some degree, dogs will scavenge and eat vegetation in the wild, so it seems likely that many dogs will tolerate some vegetable matter without problems. But figuring out which vegetables are appropriate can be challenging. And we find they can be problematic in general for dogs with weight problems, or digestive issues.

We typically rely on the predigested plant matter of green tripe and leave decisions about feeding vegetables to clients under the recommendations of reputable sources, such as Dr Karen Becker. We do ask clients to keep us informed of what they’re feeding and to withhold vegetables if their pet is having digestive issues.

In addition to adding to the carbohydrate load of the diet, some vegetables contain antinutrients. Let’s discuss some of those - :

● Glucosinolates (ref31, ref32) in cruciferous vegetables can

○ prevent iodine absorption, which may then interfere with thyroid function and cause goiter

○ affect renal/hepatic function

It is hard to find data specific to cats and dogs, however research shows that ruminants (herbivores) have relatively high tolerance to glucosinolates, while pigs (omnivores) have low tolerance. This may suggest that cats and dogs are likely to have low tolerance.

● Lectins 33 in legumes and grains can interfere with the absorption of calcium, iron, phosphorus, and zinc.

● Oxalates (ref 34 , ref 35 ) in leafy greens may bind serum calcium, contribute to urinary tract stones, and cause gastroenteritis.

● Phytates (ref 36 ) (in grains, seeds, legumes, and nuts) may inhibit absorption of iron, zinc, magnesium, and calcium. Dietary/organic sourced zinc is less susceptible to phytate-inhibition, so theoretically raw-fed pets should be more resistant to this interaction.

● Thiamine 37 deficiency can be fatal. Fruits and vegetables such as blueberries and red cabbage destroy thiamine. The impact has not been studied in dogs and cats, however it is a theoretical risk.

● Canine Dilated Cardiomyopathy 38 - we still have a lot to learn onthis issue, but it seems to be pretty well accepted that it is related to the vegetable content of grain-free diets.

● Gluten/Oats/Fibre - a study39in the ‘Journal of the American Medical Association - Paediatrics’ showed that high childhood intakes of these correlate with the development of autoimmune disease. There are so many other studies about the negative impacts of gluten and grains that we recommend absolutely avoiding them.

● Fibre is believed to be beneficial in humans largely because it undergoes anaerobic bacterial fermentation in the large bowel, giving rise to short chain fatty acids (which promote and maintain a healthy gut wall, and control inflammation). Humans, dogs and cats have no requirement for carbohydrates, and therefore fibre, as an essential nutrient. It has been demonstrated in cheetahs 40 that connective tissue and other nondigestible animal matter (bones, tendons, cartilage, hair, feathers) act as substrates for large bowel microbes, giving rise to plentiful SCFAs and other beneficial compounds. Unfortunately, the value of plant fibre has been overemphasised in humans, and anthropomorphised to pets. Despite a widespread campaign to the contrary, there are numerous studies showing a detrimental effect of fibre on human health. (ref 41)

Freeze-drying is a really useful option for raw feeders, and it can reduce microbial loads.

We do freeze-dry some of our products to use in addition to a frozen raw diet. It is handy for pet owners going away on holiday, or for when someone is pet-sitting. We don’t recommend feeding freeze-dried as the main diet, however, because it may result in suboptimal gastric acidity.

Lichtenberger (1982) described the effect of freeze-drying on gastric acidity:
“lyophilization (freeze-drying) resulted in a significant 50% reduction on the diet’s ability to stimulate [gastrin] release.”28

Those with impaired gastric acidity are at greater risk of food-bourne illness. (ref 42, ref 43) A healthy carnivore is generally well equipped with gastric secretions and microbes which allows them to safely digest44 high bacterial loads.

1) FORMULATE USING NUTRITIONAL ECOLOGY

It is clear, from both an evolutionary perspective and from nutritional analysis of prey species 45 , that a well planned raw diet provides an appropriate range and balance of micronutrients from which the individual pet can absorb and utilise nutrients to meet their needs. Evolution has provided us with most of what we need to know for this. The fact that dogs have survived well over 100,000 years on a predominantly prey-based diet speaks volumes for the suitability of a prey-based diet.

We ‘loosely’ formulate, based on nutritional ecology and evolutionary science. We know that wild dogs and cats consume wild prey. They usually consume more than one species, and they eat a variable ratio of meat, bone, organs and tripe. It is somewhat easier to balance a diet for carnivores, relative to other classifications, given that:

“prey are less variable in nutrient composition than the foods of herbivores and omnivores”

Wild canids may, to a varying degree, eat some plant matter too. This plant mmatter is not the same as the fruit and vegetables available in your local supermarket, and we have discussed potential issues with the types of plant matter that people might feed their pets. We keep it simple by feeding a small amount of plant matter in the form of stomach contents (green tripe).

Macronutrient studies have shown us that protein and fat are the most important macronutrients, and that protein levels are the key to balancing intake. Raubenheimer et al have established macronutrient preferences for dogs (30% protein:63% fat:7% carb 46) and cats (52% protein:36% fat:12% carb 47). Bear in mind that - although dogs, cats, and even humans have no established requirement for carbohydrates - these studies included various levels of carbohydrate in order to factor in the reality that most modern petfoods will contain carbohydrates.

“For most carnivores, the relevant macronutrient space is two-dimensional: protein and fat are the most important macronutrients, whereas carbohydrate is rare in natural foods and plays a lesser role in nutritional regulation.”47

Cats and dogs (and humans, as it turns out) eat to satisfy their protein requirements. If more of their diet consists of carbohydrates, they will try and eat their way through the excess carbs in order to reach their inherent protein goals. This happens with fat, but to a much lesser extent.

“when confined to diets that prevented them from achieving the target intake, the cats showed a complex pattern of compromises. On low-protein diets they overate both fat and carbohydrate to approach their target protein intake, but carbohydrate represented more of an impediment to protein gain than did fat.”47

“When unsuccessful [at reaching optimal protein intake], cats fed commercial foods will be held in a chronic state of nutritional imbalance. This raises welfare concerns, and will also in the long term likely affect cat metabolism and health.”47

Cats and dogs46 have both been shown to balance their own diets when offered a range of foods. On a varied raw diet, we have some room to move with our fat and protein levels.

“cats are better adapted to deal with variation in the protein to fat balance of their diet than the protein to carbohydrate balance, which probably reflects the low levels of carbohydrate in their pre-domesticated ancestral diets” 47

This may explain to some extent what we regularly see in practise: our dog and cat owners tell us that their pets will often change their product preferences over time - one week, their pet may prefer rabbit legs; the next they may opt for wallaby mince. Our clients become very intune with the dietary choices of their pets.

“If given the opportunity, cats are capable of composing the preferred diet by mixing their intake from nutritionally complementary foods, but in reality they are seldom provided by their owners the luxury of several complementary foods.”47

It is a uniquely satisfying aspect of our diet of mixed, raw prey that we are able to give some credence to the innate abilities of our domestic carnivores to participate in managing their own food selection.

So we advise our clients thus: feed a mix of raw meat, bones, organs and tripe from a range of prey species. Feed an amount that maintains your pet at an ideal weight. While some clients find the lack of prescriptiveness initially unnerving (it’s funny how simplicity can be scary when we are used to being told that nutrition is such a complex beast), this soon changes to a feeling of empowerment when clients realise that they are well-educated raw feeders who know exactly how to feed their pet. In fact, clients often tell us that they have re-learned their own relationship with food after experiencing the joys of real-feeding their pets.

2) TESTING

Whilst we are focused on a whole food approach, we understand that vets with conventional nutrition training will often question the nutritional completeness of our diets. Nothing unnerves the reductionist nutritionist quite so much as the absence of a nutritional panel.

Each pet that we feed is a little different. The diet will be tailored to them, and will change over time, and with seasons. This renders accurate ‘complete and balanced’ testing impossible.

We do some testing to help reassure vets of the suitability of our diet for domestic carnivores. Our testing is targeted on common areas of concern. We generally test a sample ‘average’ diet that has been minced together, as well as a selection of individual products. In addition to general macro and micronutrient panels, some of the things we have specifically tested for include:

● Calcium:Phosphorus ratios (for growing dogs)
● Fat content (for pancreatitis diets)
● Taurine and thiamine (particularly for cats)

3) NUTRITIONAL AIDS

The majority of our clients do very well on their diets of meat, bones, organs and tripe. We may use nutritional aids in our protocols for those with clinical conditions.

Bone broth: As discussed earlier, this is the basis of our gut healing protocols. We make our own bone broth and supply it in frozen sachets. Alternatively, we teach clients how to use our meaty bones to make their own if they choose.

Probiotics: Whilst we aim to influence the microbiome through appropriate food, beneficial microbe supplementation may help influence the environment in the gut. We use a range of probiotics including spore based products.

Digestive enzymes/aids: These are particularly for dogs with challenged gastric acidity due to aging, medications, disease and anxiety.

Herbal: We use this for gastric acidity support, liver tonic, microbiome influence

Glandulars: Whilst we have as much organ variety as possible within our frozen product range, we also use freeze dried organ products to provide nutrient boosts and support the corresponding organs.

Blended food supplement: Our freeze dried blend of bones, tendons, cartilage and organs is a useful nutrient boost to use in our short term protocols, and to provide additional substrates for large bowel microbes.

4) CLINICAL EXPERIENCE

We moved a snifter more toward the formulated end of the spectrum for our ‘prescription’ diets - designed for pets with clinical conditions.

The usefulness of providing optimal nutrients is limited by the ability of an individual animal to absorb and utilise them: without a well functioning gut, those nutrients may just go to waste. We address nutrition, stress, lifestyle and environmental factors as much as possible.

Our clinical cases are closely monitored by our veterinary support team and in-store case managers. Most of these protocols begin with novel meats poached in bone broth. This easily digestible phase gives the gut a chance to rest, and inflammation a chance to settle.

Bone broth contains an array of amino acids known to be immunomodulatory. Mouse studies have shown that they can significantly
reduce gut inflammation. Bone broth is similar in composition to EEN (exclusive enteral nutrition) drinks that are given to hospitalised sufferers of severe gut inflammation, to heal their mucosal lining. Studies (ref 48 , ref 49 ) have shown these drinks to be more effective than steroid treatment for inducing remission in Crohn's disease patients.

Once we are satisfied that the digestive tract is settled, we proceed gradually towards a maintenance raw diet by introducing the various
components in a stepwise fashion: raw meat, minced bone, tripe, organs, and whole bones from a variety of sources. We tailor this to each individual pet, using our clinical experience and extensive product range.

We consider each clinical case, in its entirety, as to whether we can accommodate them with our food, within our recommendations. Very occasionally we may advise a client and their veterinarian that a switch to a raw diet would not be advisable.

Sometimes we face a challenging situation in which we feel that a change to raw is appropriate, the primary veterinarian disagrees, but the client wishes to proceed with the change against their vet’s advice. In most cases, we are able to resolve the conflict with some sensitive diplomacy.

It’s interesting to look at processed prescription diets, and their main variations from regular commercial pet foods. Many actually seem to be taking steps towards a raw diet by:

• improving omega ratios
• boosting vitamin B content
• lowering carbohydrate
• glucosamine/chondroitin supplementation
• improving protein sources, adding amino acids (taurine, L-carnitine)
• avoiding excess copper
• adding antioxidants

Why wouldn’t they want many of these enhancements in every commercial diet?

There is yet much to be learnt about the nutritional management of disease states, for raw diets and in general. Following are some thoughts on a few of the more challenging ones:

Hyperlipidaemia

Primary veterinarians may ask us to formulate low-fat diets for their hyperlipidaemia patients. It is a complex disease, especially where genetics are a factor (ie in schnauzers). We do not yet have canine hyperlipidaemia studies examining a range of fat and carbohydrate contents within the context of a raw diet. There is growing evidence in the human realm to suggest it’s more of a carbohydrate issue than a fat issue:

“This meta-analysis suggests that low-carbohydrate diets are effective at improving weight loss, HDL and TG lipid profiles.”

“The consumption of diets rich in carbohydrates have been shown to promote elevations in circulating lipids. In particular, the consumption of monosaccharides, such as glucose and fructose, have been shown to induce increases in intestinal de novo lipogenesis, as well as be used as a substrate for the synthesis of triglycerides and lipoprotein export in the form of chylomicrons.”51

So currently we use the product testing that we have done to identify our lower fat products. Our diet is already essentially carbohydrate-free.

Whilst we’ve helped a small number of cases somewhat, we look forward to following more as suitable cases present.

Cystine uroliths

Research (ref52 , ref53) suggests there are many more Type 3’s (androgen dependent mutation) than once thought, which is consistent with what we have observed in recent cases which have responded well to neutering and the stones haven’t recurred on a maintenance raw diet. Obviously, these need careful monitoring.

Ammonium urate uroliths

A low purine raw diet can be successful. This involves avoiding the particularly nutritious organs, seafood and wild prey, however it is still a more appealing option for many than long term u/d.

Renal disease

It is commonly believed that reducing protein, and more especially phosphorus intake is the cornerstone of treating renal disease. A deeper look into the science raises some questions around this approach.

Finco et al 54 found that dog survival was significantly enhanced by 0.4% (vs 1.4%) P diets, however the amount of dietary protein was not a significant factor. Urine protein excretion was not affected by the amount of protein or P in the diet. They also found 55 that protein restriction was not helpful for cats:

“Diets replete in protein were not associated with increased severity of glomerular or nonglomerular renal lesions, increased proteinuria, or decreased GFR... Results raise questions about the practice of restricting quantity of protein in the diet of cats with chronic renal failure, with the intention of ameliorating development of further renal damage.”

It is important to maintain adequate protein levels to avoid wasting. This is easily done on a raw diet.

The amount of phosphorus in the diet may be less important than the type of phosphorus. As discussed earlier, phosphorus from a natural source is absorbed and utilised in a different manner compared to the synthetic sources in processed food. While we can alter our diets to reduce phosphorus somewhat, and will do this when a primary veterinarian requests it, experience has shown us that normal calcium:phosphorus ratios in a well-planned raw diet can successfully support renal pets.

“Look deep into nature, and then you will understand everything better.” (Albert Einstein)

First and foremost, we believe that the very best diets consist of species-appropriate, real food. This concept is one-size-fits-all.

The details within this concept may differ along various lines, formulation being one of them. We acknowledge that high quality raw diets can fit within a range of formulation types.

We sit comfortably and confidently on the minimal formulation end of the spectrum - as close to nature as we can be, within the confines of modern life.

Excerpt from ‘Nourishment’ by Fred Provenza

“To live, mountain man, coyote, raven, and eagle participate in an act as old as life: energy and matter endlessly changing forms. By demand and by design, organisms consume matter and energy to maintain form and sustain function. From time immemorial, life didn’t ponder what or how to eat. Organisms don’t know energy, protein, minerals or vitamins as we discern them from lab analyses. They have no concerns about eating red meat or brains, internal organs or greasy fleece, or ratios of omega-3 to omega-6 polyunsaturated fatty acids. Those matters were beside the point for mountain men and equally irrelevant for the coyotes, ravens and golden eagle assembled on that grassy knoll. Nature, in the form of an antelope, provided a feast, and they savoured every morsel on that clear, cold winter night. Soon, coyotes, ravens and eagles will become food for soil micro- and macro-fauna, which will become plant, which will become herbivore, omnivore, and carnivore yet again, which will become soil, in endless transformation.”

Please direct any questions or feedback to Dr Rebecca Brown, support@rawessentials.co.nz

1. Fagan, D.A. (1980) Diet consistency and periodontal disease in exotic carnivores. Proceedings of the Conference of the American Association of Zoo Veterinarians, Washington, DC, 34-37. Retrieved from http://www.colyerinstitute.org...

2. The title of an essay written in 1973 by Russian evolutionary biologist, Theodosius Dobzhansky.

3. Scrinis G. Nutritionism—the science and politics of dietary advice. Columbia University Press, New York, USA, 2013.

4. van Vliet, S., Bain, J.R., Muehlbauer, M.J. et al. A metabolomics comparison of plant-based meat and grass-fed meat indicates large nutritional differences despite comparable Nutrition Facts panels. Sci Rep 11, 13828 (2021). https://doi.org/10.1038/s41598...

5. Zicker S, Schoenherr B. Focus on nutrition: the role of iodine in nutrition and metabolism. Compend Contin Educ Vet. 2012 Oct;34(10):E1-4. PMID: 23532759.

6. Gibson RS. The role of diet- and host-related factors in nutrient bioavailability and thus in nutrient-based dietary requirement estimates. Food Nutr Bull. 2007 Mar;28(1 Suppl International):S77-100. doi: 10.1177/15648265070281S108. PMID: 17521121.

7. National Research Council. 2006. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press. https://doi.org/10.17226/10668.

8. Wedekind KJ, Blumer ME, Huntington CE, Spate V, Morris JS. The feline iodine requirement is lower than the 2006 NRC recommended

allowance. J Anim Physiol Anim Nutr (Berl). 2010 Aug 1;94(4):527-39. doi: 10.1111/j.1439-0396.2009.00940.x. Epub 2009 Nov 11. PMID: 19906136.

9. Davies, M., Alborough, R., Jones, L. et al. Mineral analysis of complete dog and cat foods in the UK and compliance with European guidelines. Sci Rep (2017) 7, 17107 https://doi.org/10.1038/s41598...

10. Hendriks, WH; Tarttelin, MF. Nutrient composition of moist cat foods sold in New Zealand. Proceedings of the Nutrition Society of New Zealand (1997), 22:202-207

11. Markovich JE, Freeman LM, Heinze CR. Analysis of thiamine concentrations in commercial canned foods formulated for cats. J Am Vet Med Assoc. 2014 Jan 15;244(2):175-9. doi: 10.2460/javma.244.2.175. PMID: 24378026.

12. Ricci R, Granato A, Vascellari M, Boscarato M, Palagiano C, Andrighetto I, Diez M, Mutinelli F. Identification of undeclared sources of animal origin in canine dry foods used in dietary elimination trials. Anim Physiol Anim Nutr (Berl). 2013 May;97 Suppl 1:32-8. doi: 10.1111/jpn.12045. PMID: 23639015.

13. Raditic DM, Remillard RL, Tater KC. ELISA testing for common food antigens in four dry dog foods used in dietary elimination trials. J Anim Physiol Anim Nutr (Berl). 2011 Feb;95(1):90-7. doi: 10.1111/j.1439-0396.2010.01016.x. Epub 2010 Oct 29. PMID: 21039924.

14. Gosper EC, Raubenheimer D, Machovsky-Capuska GE, Chaves AV., Discrepancy between the composition of some commercial cat foods and their package labelling and suitability for meeting nutritional requirements. Aust Vet J (2016) Jan-Feb;94(1-2):12-7. doi: 10.1111/avj.12397

15. Hodgkinson, S. M., Rosales, C. E., Alomar, D., & Boroschek, D.. (2004). Chemical-nutritional evaluation of commercial dry food in Chile for adult dogs in maintenance. Archivos de medicina veterinaria, 36(2), 173-181. https://dx.doi.org/10.4067/S03...

16. Anna J. Duffield-Lillico, Colin B. Begg, Reflections on the Landmark Studies of β-Carotene Supplementation. JNCI: Journal of the National Cancer Institute, Volume 96, Issue 23, 1 December 2004, Pages 1729–1731, https://doi.org/10.1093/jnci/d...

17. Coltherd JC, Staunton R, Colyer A, et. al. Not all forms of dietary phosphorus are equal: an evaluation of postprandial phosphorus concentrations in the plasma of the cat. Br J Nutr (2019) Feb;121(3):270-284. doi: 10.1017/S0007114518003379

18. Alexander J, Stockman J, Atwal J, et. al., Effects of the long-term feeding of diets enriched with inorganic phosphorus on the adult feline kidney and phosphorus metabolism. Br J Nutr (2018) Dec 21;121(3):1-21. doi: 10.1017/S0007114518002751

19. Karen J. Wedekind, Stephen R. Lowry, Are Organic Zinc Sources Efficacious in Puppies?, The Journal of Nutrition, Volume 128, Issue 12, December 1998, Pages 2593S–2595S, https://doi.org/10.1093/jn/128...

20. Manson JE, Bassuk SS. Vitamin and Mineral Supplements: What Clinicians Need to Know. JAMA. 2018;319(9):859–860. doi:10.1001/jama.2017.21012

21. Lerner A, Matthias T. Changes in intestinal tight junction permeability associated with industrial food additives explain the rising incidence of autoimmune disease. Autoimmun Rev. 2015 Jun;14(6):479-89. doi: 10.1016/j.autrev.2015.01.009. Epub 2015 Feb 9. PMID: 25676324.

22. Craig, J.M., Additives in pet food: are they safe? J Small Anim Pract (2021), 1–12 https://doi.org/10.1111/jsap.1...

23. Chandler M, Cunningham S, Lund EM, Khanna C, Naramore R, Patel A, Day MJ. Obesity and Associated Comorbidities in People and Companion Animals: A One Health Perspective. J Comp Pathol. 2017 May;156(4):296-309. doi: 10.1016/j.jcpa.2017.03.006. Epub 2017 Apr 28. PMID: 28460795.

24. Raubenheimer D, Machovsky-Capuska GE, Gosby AK, Simpson S. Nutritional ecology of obesity: from humans to companion animals. Br J Nutr. 2015 Jan;113 Suppl:S26-39. Doi:10.1017/S0007114514002323. Epub 2014 Nov 21. PMID: 25415804.

25. Linda P. Case, Leighann Daristotle, Michael G. Hayek, Melody Foess Raasch, Chapter 12 - Protein Requirements, Canine and Feline Nutrition (Third Edition), Mosby, 2011, Pages 89-106, (https://www.sciencedirect.com/... 10012X)

26. Saint-Hilaire, S.,Lavers, M.K., Kennedy, J. & Code, C.F. (1960). Gastric acid secretory value of different foods. Gastroenterology,

27. Lennard-Jones, J.E., Fletcher, J. & Shaw, D.G. (1968). Effect of different foods on the acidity of the gastric contents in patients with duodenal ulcer. Gut (BMJ), 9, 177-182.

28. Lichtenberger, L.M. (1982). Importance of food in the regulation of gastrin release and formation. American Journal of Physiology 243, G429-441.

29. Brooks, F.P. (1985). Effect of diet on gastric secretion. American Journal of Clinical Nutrition, 42, 1006-1019.

30. DelValle, J. & Yamada, T. (1990). Amino acids and amines stimulate gastrin release from canine antral G-cells via different pathways. Journal of Clinical Investigation, 85, 139-143

31. Alexander, J., Auðunsson, G.A., Benford, D. et al (2008). Glucosinolates as undesirable substances in animal feed. European Food Safety Authority Journal, 590, 1-76. doi:https://doi.org/10.2903/j.efsa...

32. Tripathi, M.K. & Mishra, Awadhesh. (2007). Glucosinolates in animal nutrition: A review. Animal Feed Science and Technology - ANIM FEED SCI TECH. 132. 1-27. 10.1016/j.anifeedsci.2006.03.003.

33. Harvard T.H. Chan School of Public Health, Lectins, https://www.hsph.harvard.edu/n...

34. Botha CJ, Penrith ML. Potential plant poisonings in dogs and cats in southern Africa. J S Afr Vet Assoc. 2009 Jun;80(2):63-74. doi: 10.4102/jsava.v80i2.173. PMID: 19831265.

35. Craig JM. Food intolerance in dogs and cats. J Small Anim Pract 2019;60(2):77-85.

36. Pereira AM, Guedes M, Matos E, Pinto E, Almeida AA, Segundo MA, Correia A, Vilanova M, Fonseca AJM, Cabrita ARJ. Effect of Zinc Source and Exogenous Enzymes Supplementation on Zinc Status in Dogs Fed High Phytate Diets. Animals (Basel). 2020 Feb 29;10(3):400. doi: 10.3390/ani10030400. PMID: 32121315; PMCID: PMC7142709.

37. Kritikos, G., Parr, J. M., & Verbrugghe, A. (2017). The Role of Thiamine and Effects of Deficiency in Dogs and Cats. Veterinary Sciences, 4(4), 59. https://doi.org/10.3390/vetsci...

38. Smith, C.E., Parnell, L.D., Lai, CQ. et al. Investigation of diets associated with dilated cardiomyopathy in dogs using foodomics analysis. Sci Rep 11, 15881 (2021). https://doi.org/10.1038/s41598...

39. Andrén Aronsson C, Lee H, Hård af Segerstad EM, et al. Association of Gluten Intake During the First 5 Years of Life With Incidence of Celiac Disease Autoimmunity and Celiac Disease Among Children at Increased Risk. JAMA. 2019;322(6):514–523. doi:10.1001/jama.2019.10329

40. Depauw S, Hesta M, Whitehouse-Tedd K, Vanhaecke L, Verbrugghe A, Janssens GP. Animal fibre: the forgotten nutrient in strict carnivores? First insights in the cheetah. J Anim Physiol Anim Nutr (Berl). 2013 Feb;97(1):146-54. doi: 10.1111/j.1439-0396.2011.01252.x. Epub 2011 Nov 10. PMID: 22074361.

41. Peery, A. F., Barrett, P. R., Park, D., Rogers, A. J., Galanko, J. A., Martin, C. F., & Sandler, R. S. (2012). A high-fiber diet does not protect against asymptomatic diverticulosis. Gastroenterology, 142(2), 266–72.e1. https://doi.org/10.1053/j.gast...

42. Wei, L., Ratnayake, L., Phillips, G., McGuigan, C. C., Morant, S. V. Flynn, R. W., Mackenzie, I. S., and MacDonald, T. M. (2017) Acid-suppression medications and bacterial gastroenteritis: a population-based cohort study. Br J Clin Pharmacol, 83: 1298– 1308. doi: 10.1111/bcp.13205.

43. Smith JL. The role of gastric acid in preventing foodborne disease and how bacteria overcome acid conditions. J Food Prot. 2003 Jul;66(7):1292-303. doi: 10.4315/0362-028x-66.7.1292. PMID: 12870767.

44. Callaway, E. Microbes help vultures eat rotting meat. Nature (2014). https://doi.org/10.1038/nature...

45. Dierenfeld, E. S., Alcorn, H. L., & Jacobsen, K. L. (2002). Nutrient composition of whole vertebrate prey (excluding fish) fed in zoos Published by: U.S. Dept. of Agriculture, Agricultural Research Service, National Agricultural Library, Animal Welfare Retrieved from purl.access.gpo.gov/GPO/LPS80845

46. Hewson-Hughes AK, Hewson-Hughes VL, Colyer A, Miller AT, McGrane SJ, Hall SR, Butterwick RF, Simpson SJ, Raubenheimer D. Geometric analysis of macronutrient selection in breeds of the domestic dog, Canis lupus familiaris. Behav Ecol. 2013 Jan;24(1):293-304. doi: 10.1093/beheco/ars168. Epub 2012 Dec 17. PMID: 23243377; PMCID: PMC3518205

47. Raubenheimer D, Machovsky-Capuska GE, Gosby AK, Simpson S. Nutritional ecology of obesity: from humans to companion animals. Br J Nutr. 2015 Jan;113 Suppl:S26-39. doi: 10.1017/S0007114514002323. Epub 2014 Nov 21. PMID: 25415804.

48. Van Limbergen, J., Haskett, J., Griffiths, A. M., Critch, J., Huynh, H., Ahmed, N., deBruyn, J. C., Issenman, R., El-Matary, W., Walters, T. D., Kluthe, C., Roy, M. E., Sheppard, E., Crandall, W. V., Cohen, S., Ruemmele, F. M., Levine, A., & Otley, A. R. (2015). Toward enteral nutrition for the treatment of pediatric Crohn disease in Canada: a workshop to identify barriers and enablers. Canadian journal of gastroenterology & hepatology, 29(7), 351–356. https://doi.org/10.1155/2015/5...

49. Wall C, L, Gearry R, B, Day A, S: Treatment of Active Crohn’s Disease with Exclusive and Partial Enteral Nutrition: A Pilot Study in Adults. Inflamm Intest Dis 2017;2:219-227. doi: 10.1159/000489630

50. Chawla S, Tessarolo Silva F, Amaral Medeiros S, Mekary RA, Radenkovic D. The Effect of Low-Fat and Low-Carbohydrate Diets onWeight Loss and Lipid Levels: A Systematic Review and Meta-Analysis. Nutrients. 2020; 12(12):3774. https://doi.org/10.3390/nu1212...

51. Hoffman, Simona,b,*; Alvares, Daniellea,b,*; Adeli, Khosrowa,b Intestinal lipogenesis, Current Opinion in Clinical Nutrition and Metabolic Care: July 2019 - Volume 22 - Issue 4 - p 284-288. doi: 10.1097/MCO.0000000000000569

52. Florey J, Ewen V, Syme H. Association between cystine urolithiasis and neuter status of dogs within the UK. J Small Anim Pract. 2017 Sep;58(9):531-535. doi: 10.1111/jsap.12707. Epub 2017 Jul 5. PMID: 28678386.

53. Hesse, Albrecht & Hoffmann, Jenni & Orzekowsky, Helmut & Neiger, Reto. (2016). Canine cystine urolithiasis: A review of 1760 submissions over 35 years (1979–2013). The Canadian Veterinary Journal. 57. 277-281.

54. Finco DR, Brown SA, Crowell WA, Duncan RJ, Barsanti JA, Bennett SE. Effects of dietary phosphorus and protein in dogs with chronic renal failure. Am J Vet Res. 1992 Dec;53(12):2264-71. PMID: 1476305.

55. Finco DR, Brown SA, Brown CA, Crowell WA, Sunvold G, Cooper TL.Protein and calorie effects on progression of induced chronic renal failure in cats. Am J Vet Res. 1998 May;59(5):575-82. PMID: 9582959.