The Heart of the Matter

In mid-July, the U.S. Food and Drug Administration (FDA) released an alert to veterinarians and pet owners regarding reports of increased incidence of a heart disease called canine dilated cardiomyopathy (DCM). This disorder is characterized by weakening of the heart muscle, which leads to a decreased ability of the heart to pump, and if untreated, to cardiac failure. The reported cases occurred in breeds that are not considered to be genetically predisposed to this disorder.

Further, a significant number of the dogs were found to have reduced levels of circulating taurine in their blood and have responded positively to taurine supplementation. It is speculated that these cases are related to the consumption of foods that negatively affect taurine status, leading to taurine-deficiency DCM. Foods containing high levels of peas, lentils, other legume seeds, or potatoes were identified by the FDA as potential risk factors. These ingredients are found commonly in foods that are formulated and promoted as “grain-free.”

As these things go, there followed a lot of hype and a fair bit of hysteria in response. Let us avoid this type of reaction and instead look at the evidence – what do we currently know about the role of diet and taurine in the development of DCM in dogs and how is it that “grain-free” foods have been recently targeted as a possible dietary cause?

What is Taurine? The nutrient taurine is a unique type of amino acid, called a beta-amino sulfonic acid. It is not incorporated into proteins but rather is found primarily as a free amino acid in body tissues and circulating in the blood. Taurine has many functions, but two that are important for this discussion involve its role in normal heart function and its presence as a component of bile acids, which are needed for fat digestion. Most animals obtain adequate taurine to meet their needs by producing it endogenously (in the body) from two other amino acids, methionine and cysteine.

TAURINE

This means that while animals require taurine physiologically, most do not have a dietary requirement for taurine. The exception to this rule is the cat. Cats (but not dogs) always require a source of taurine in their food. If they do not have it, one of the diseases that they can develop (and possibly die from) is……you guessed it…..DCM.

Taurine-deficiency DCM is well documented in cats. We also know quite a lot about the dietary factors that contribute to this disease in that species. In contrast, dogs (usually) do not require a source of dietary taurine. However, we know that some dogs still develop taurine-deficiency DCM. Why does this happen? The history of DCM in cats can help in untangling what may be occurring in dogs.

Taurine-deficiency DCM in Cats: Looking back, I cannot avoid a sense of déjà vu. In the early 1980s veterinarians began reporting increased incidences of DCM in pet cats. By 1987, a role for dietary taurine was suspected. In a seminal study, a veterinary researcher at UC Davis reported low plasma (blood) taurine levels in 21 cats with clinical signs of DCM (1). When the cats were supplemented with taurine, all 21 completely recovered from the disease. This discovery led to a series of controlled studies that supported the existence of taurine-deficiency DCM developing in cats who were fed diets that contained sufficient concentrations of taurine.

What was going on?

It has to do with Bile Acids: Another role of taurine is the body is that it is necessary for normal bile acid function. Taurine is linked to bile acids in the liver to form bile salts. These compounds are secreted into the small intestine during digestion where they function to aid in fat digestion. Animals are very efficient at conserving the taurine that is secreted into the intestine by reabsorbing the bile salts back into the body further down the intestinal tract. This occurs through a process called “enterohepatic reutilization” and prevents a daily loss of taurine in the feces.

Herein lies the problem for cats with DCM: If anything happens during digestion that causes the degradation of the bile salt taurine or that inhibits its reabsorption into the body, more is lost in the feces. If this happens consistently, the cat will experience an increase in his or her daily need for dietary taurine. Simply put – if anything causes the cat to poop out more taurine-bile acid complexes (or their degraded by-products), the cat will be in danger of a taurine deficiency if a higher level is not provided in the diet.

This is exactly what was happening in the cats with taurine-deficiency DCM – and is possibly what we are seeing today in dogs. The difference is that we know what diet factors caused taurine deficiency in cats during the late 1980s. These factors are not yet fully understood for dogs (but we can make a few guesses).

Here is What We Know: The studies with cats found that several dietary factors influenced taurine status (2,3,4). These were the level and type of dietary protein, the amount and type of dietary fiber, and the degree of heat treatment that was used during food processing. These factors could affect taurine status in three ways:

  1. Bile Acid Binding: Certain fibers and peptides (small protein chains) in the food can bind with bile salts the small intestine and make them unavailable for reabsorption into the body. This results in an increased daily loss of taurine in the feces and a subsequent increase in daily taurine requirement to replace that loss.
  2. Increased Microbial Degradation: Thermal processing of protein (extrusion or canning) can lead to the production of Maillard products – complexes of sugars and amino acids and are poorly digested in the small intestine. The undigested complexes travel to the large intestine and provide an intestinal environment that favors increased numbers of taurine-degrading bacteria. An increase in these bacterial populations reduces the proportion of taurine that is available for reabsorption and reuse by the body.
  3. Reduced Taurine Availability: Taurine is found naturally in animal-based proteins but is not found in plant-based protein sources. Therefore, providing diets that include a sufficient level of high-quality animal proteins (that are not heat damaged) should ensure adequate taurine intake. However, protein that is of low quality or that has been excessively heat-treated will be poorly digested, reducing the availability of taurine and of its precursor amino acids, cysteine and methionine. (Note: Cats produce small amounts of taurine from these precursors, while dogs can produce all of their needs from them, if adequate levels are available).

In response to new information regarding the interaction of dietary factors and taurine status in cats (and their relationship to DCM in cats), the Association of American Feed Control Officials (AAFCO) increased the recommendations for dietary taurine in extruded and canned cat foods in the early 1990s. The current recommendations are 1000 mg taurine/kg (0.1 %) in dry (extruded) cat foods and 2000 mg taurine/kg (0.2 %) in canned cat foods.

So, What about Dogs? Unlike the cat, dogs that are fed diets containing adequate levels of protein should be capable of synthesizing enough taurine from the two amino acid precursors, cysteine and methionine, to meet their needs. Therefore, a requirement for dietary taurine has not been generally recognized in dogs.

Breed Predispositions: However, there is evidence – evidence that we have had for at least 15 years – that certain breeds of dogs, and possibly particular lines within breeds, exhibit a high prevalence of taurine-deficiency DCM. Genetically predisposed breeds include the American Cocker Spaniel, Golden Retriever, Labrador Retriever, Saint Bernard, Newfoundland and English Setter (5,6). Although the exact underlying cause is not known, it appears that some breeds have either a naturally occurring higher requirement for taurine or a metabolic abnormality that affects their taurine synthesis or utilization.

Size: A second factor that affects taurine status in dogs is size. There is evidence that a large adult size and a relatively slow metabolic rate influences the rate of taurine production in the body and may subsequently lead to a dietary taurine requirement. It is theorized that increased body size in dogs is associated with an enhanced risk for developing taurine deficiency and that this risk may be exacerbated by a breed-specific genetic predisposition. For example, when compared metabolically, Newfoundlands have a significantly lower rate of taurine synthesis than Beagles (7).

There is additional evidence that large and giant breed dogs have lower rates of taurine production compared with small dogs. Ultimately, studies suggest that certain dogs possess a genetic predisposition to taurine depletion and increased susceptibility to taurine-deficiency DCM and that this susceptibility may be related to the combined factors of breed, size and metabolic rate.

What is the Role of Diet? The recent spate of cases and media attention to taurine-deficiency DCM in dogs suggests that this is a very new problem in dogs. However, it is not new. A connection between diet and DCM in dogs was first described in a paper published in the Journal of the American Veterinary Medical Association in 2001 (8). What is new is the sudden focus on certain pet food ingredients and the target that appears to have been placed upon the backs of all “grain-free” pet food brands by some bloggers and veterinarians. Not to put too fine a point on this, but the 12 cases of taurine-deficiency DCM described in the 2001 paper were collected between 1997 and 2001, years before grain-free dog foods had arrived on the pet food scene. Rather than disparage one class or type of dog food (or pet food company), it is more important to look at specific dietary factors that may be involved in DCM in dogs.

Generally speaking, these are expected to be the same as those identified for cats, including low protein levels, poorly processed or heat-damaged proteins (leading to Maillard products), and the inclusion of a high proportion of plant-based protein sources such as peas and legumes.

Over the past 15 years, reduced taurine status in dogs has also been alternately associated with feeding lamb meal and rice diets, soybean-based diets, rice bran, beet pulp, and high fiber diets (9,10,11). As with cats, there appear to be multiple dietary (and genetic) factors involved. For example, it was theorized that the perceived (not proven) association between lamb meal and taurine status was due to low levels of available amino acids present in the lamb meal, or to excessive heat damage of the protein, or to the confounding factor of the inclusion of rice bran in many lamb meal-containing foods. To date, none of these factors have been conclusively proven or disproven. Although, the most recent study showed that three types of fiber source – rice bran, cellulose, and beet pulp – all caused reduced plasma taurine levels in dogs when included in a marginally low protein diet, with beet pulp causing the most pronounced decrease (11).

Complicated? You bet. This is why it is important to avoid making unsupported claims about certain foods and brands. Taurine-deficiency DCM has been around for a while in dogs and continues to need study before making definitive conclusions about one or more specific dietary causes.

What DO we know? We know that any dietary factor that reduces the availability of taurine precursors, binds taurine bile salts in the intestine, or causes an increase in the bacteria populations that degrade taurine can reduce a dog’s ability to synthesize taurine or will increase taurine degradation and/or loss in the feces. These changes could ultimately compromise a dog’s taurine status (especially if the dog was genetically predisposed) and affect heart health. In extreme cases, as we are seeing, this can lead to taurine-deficiency DCM (see diagram below).

FDA Report: The FDA report identified foods that contain high amounts of peas, lentils, legume seeds, or potatoes to be of potential concern. The FDA also stated that the underlying cause of DCM in the reported cases is not known and that at this time, the diet-DCM relationship is only correlative (not causative). However, this has not stopped various bloggers and even some veterinarians from targeting small pet food companies and/or grain-free brands of food, and implying that these foods, and these foods alone, are causing taurine-deficiency DCM in dogs. Their reasoning is that peas and legumes are present in high amounts in foods that are formulated and marketed as grain-free. However, the truth is that many companies and brands of food include these ingredients. More importantly, there is no clear evidence showing that a particular dog food type, brand, or even ingredient is solely responsible for taurine-deficiency DCM in dogs.

Rather, it is more reasonable and responsible to speculate that one or more of these ingredients, their interactions, or the effects of ingredient quality, heat treatment, and food processing may play a role. Furthermore, the underlying cause could be the protein, starch, or fiber fractions of these ingredients. As plant-source proteins, peas and lentils and legumes include varying amounts of starch (both digestible and resistant forms) and dietary fiber. These protein sources are also generally less nutritionally complete and less digestible than are high quality animal source proteins – additional factors that could influence a dog’s ability to both produce and use taurine. Potatoes, on the other hand, provide a digestible source of starch in an extruded food but also contain varying levels of resistant starch, which is not digested and behaves much like dietary fiber in the intestinal tract.

The Heart of the Matter: Because any or all of these dietary factors could be risk factors for taurine-deficiency DCM in dogs and because peas, legumes, and other ingredients identified by the FDA report have not yet been fully studied, the heart of the matter is that no conclusions can yet be made about the underlying dietary cause or causes of taurine-deficiency DCM in dogs. Given what we do know, a recommendation is to feed a food that contains sufficient levels high quality, animal-source protein, does not include plant-source proteins as its primary protein source, and does not contain high levels of dietary fiber. If you are worried about your dog’s taurine status or heart health, see your veterinarian for a complete physical examination and if needed, to measure plasma levels of taurine.

Cited Studies:

  1. Pion PD, Kittleson MD, Rogers QR, et al. Myocardial failure in cats associated with low plasma taurine: A reversible cardiomyopathy. Science 1987; 237:764-768.
  2. Earl KE, Smith PM. The effect of dietary taurine content on the plasma taurine concentration of the cat. British Journal of Nutrition 1991; 66:227-235.
  3. Hickman MA, Morris JG, Rogers QR. Effect of processing on the fate of dietary taurine in cats. Journal of Nutrition 1990; 120:995-1000.
  4. Hickman HA, Morris JG, Rogers QR. Intestinal taurine and the enterohepatic circulation of taurocholic acid in the cat. Advances in Experimental Medicine and Biology 1992; 315:45-54.
  5. Freeman LM, Rush JE, Brown DJ, et al. Relationship between circulating and dietary taurine concentrations in dogs with dilated cardiomyopathy. Veterinary Therapeutics 2001; 370-378.
  6. Backus RC, Ko KS, Fascetti AJ. Low plasma taurine concentration in Newfoundland dogs is associated with low plasma methionine and cysteine concentrations and low taurine synthesis. Journal of Nutrition 2006; 136:2525-2533.
  7. Ko KS, Backus RC, Berg JR, et al. Differences in taurine synthesis rate among dogs relate to differences in their maintenance energy requirement. Journal of Nutrition 2007; 137:1171-1175.
  8. Fascetti AJ, Reed JR, Roger QR, et al. Taurine deficiency in dogs with dilated cardiomyopathy: 12 cases (1997 – 2001). Journal of the American Animal Veterinary Association 2001; 223:1137-1141.
  9. Delaney SJ, Kass PH, Rogers QR, Fascetti AJ. Plasma and whole blood taurine in normal dogs of varying size fed commercially prepared food. Journal of Animal Physiology and Animal Nutrition 2003; 87:235-244.
  10. Torres CL, Backus RC, Fascetti AJ, et al. Taurine status in normal dogs fed a commercial diet associated with taurine deficiency and dilated cardiomyopathy. Journal of Animal Physiology and Animal Nutrition 2003; 87:359-372.
  11. Ko KS, Fascetti AJ. Dietary beet pulp decreases taurine status in dogs fed low protein diet. Journal of Animal Science and Technology 2016; 58:29-39.

Dogs and Carbs – Its Complicated

The question of how best to feed dogs stimulates great debate and evokes strong emotions among dog folks. (Yes, this an intended understatement). One of the most contentiously defended viewpoints in recent years is that dogs should not be fed diets that contain digestible carbohydrate (starch). Two primary arguments are used to defend this position.

These are:

  1. Dogs are carnivores and have no dietary requirement for carbohydrate; and
  2. Dogs are unable to efficiently digest starch. Therefore, including starch-providing ingredients in dog foods is unhealthy and provides no nutritional value.

Like many persistent beliefs, there is both truth and falsehood in these claims. Let’s start with the first.

Dogs are carnivores and have no dietary requirement for carbohydrate: The first bit is false; the second bit is true. Dogs are classified within the taxonomic order of Carnivora but like many other species within this order, dogs are omnivorous. The term omnivore simply means that an animal consumes foods that are of animal and plant origin (dogs do this) and can derive essential nutrients from both animal and plant foods (ditto). Based upon this definition, animal nutritionists consider the dog to be an omnivore. By contrast, the domestic cat, along with other felid species, is classified as an obligate carnivore. This classification means that cats cannot derive all of their nutrient needs from plant foods and therefore have an obligate need for foods of animal origin in their diet.

The fact that dogs are omnivorous does not signify that they are not predatory (they are), nor that they do not seek out and enjoy eating meat (they do). All that it means is that dogs can consume and derive nutrients from both animal and plant matter. If we consider the dog’s feeding behavior, it is clear that the majority of dogs enjoy and probably prefer to consume meat in their diet. However, they also scavenge and consume a wide variety of food types, including starch-containing foods. Nutritionally, just like bears (who also preferably seek out animal source proteins), dogs are omnivores.

Personally, I am baffled as to why “omnivore” has become a fighting word among dog people. Really? This label does not turn the dog into a carrot-munching, Birkenstock-wearing, canine hippie.

PEACE DUDE. I’M AN OMNIVORE, NOT A FIGHTER

Rather, it simply describes what the dog eats and is capable of deriving nutrients from – meat and veggies. That’s all. Time for us all to calm down about this one. Let’s move on to the second part of this claim – that dogs have no dietary requirement for carbohydrates.

So what about carbs? This part is correct. Dogs, like other animals, do not have a dietary requirement for carbohydrates. However, cooked starch provides a highly digestible energy source to dogs when included in their diet. From a nutrition standpoint, dietary carbohydrate spares protein. This means that when a body uses carbohydrate to provide needed energy, dietary protein is conserved from being used for this purpose and continues to be available for use to provide essential amino acids, build and repair body tissues, and support a healthy immune system. Therefore, including at least some digestible carbohydrate in the diet of dogs is generally considered to be beneficial. The controversy about starch in dog foods revolves more around how much starch is in the food and where that starch comes from, rather than its absolute presence or absence. Dogs can thrive on low-carbohydrate diets provided such diets are balanced and contain all of the essential nutrients. Diets formulated in this way are often highly palatable because of their high proportions of protein and fat. These foods are also generally very energy dense (lots of calories packed into a small volume of food), which means that portion control is important to ensure that dogs maintain a healthy weight.

Let’s move on to number 2 – the belief that dogs are unable to digest starch.

Dogs cannot digest starch. Unequivocally false. Dog efficiently digest cooked starch, just like humans. They cannot digest raw starch and neither can we. Cooking results in the expansion of the small granules that make up starch, which allows digestive enzymes better access and increases digestibility. This is true for humans as well as for dogs, and this fact explains why we generally do not munch on raw potatoes. We actually know the exact degree to which cooking increases digestibility of various starches. Ground grains such as rice, oats, or corn are about 60 percent digestible when fed raw to dogs. Cooking these ingredients increases the dog’s ability to digest them to almost 100 percent! This means that if you feed your dog 100 grams of uncooked oats or rice, only 60 grams will make it into his body to nourish him; 40 grams ends up in the large intestine where microbes ferment some of it, and a lot of that 40 grams ends up in your yard, as feces. Conversely, when cooked, almost the entire 100 grams are digested and absorbed to nourish your dog. Again, not to put too fine a point on this, but the same holds true for humans.

Meet AMY2B: Dogs also have an enhanced ability to digest starch-containing ingredients, a change that has been directly tied to domestication. In 2013, a ground-breaking paper by Erik Axelsson of Uppsala University in Sweden identified a host of genetic changes that occurred as dogs evolved from their wolf ancestors (1). Three of these changes were alterations of key genes that code for enzymes involved in starch digestion, most notably and consistently, one labeled AMY2B. This gene codes for the production of pancreatic amylase, an enzyme that functions to digest dietary starch.

Although variation exists among individual dogs and breeds of differing geographic origin, the increased copies of the AMY2B gene correlate with higher levels of circulating pancreatic amylase in a dog’s blood, which means that higher AMY2B leads to more efficient starch digestion (2,3,4).  On average, dogs have a sevenfold higher copy number of this gene compared with present-day wolves. These changes in the dog’s genetic makeup coincide with the expansion of human agricultural practices and increased reliance upon starch-providing plants in both human and dog diets.

What do dogs choose? It is a fact that domestic dogs are better adapted to scavenging and to a diet that is higher in starch-containing foods than were their wolf-like ancestors. However, just because dogs can consume and digest starch, it does not necessarily follow that a diet that contains a high proportion of digestible carbohydrate is the healthiest way to feed them. One way of approaching this question is to ask the dogs directly.

Historically, nutritionists have viewed diet selection in animals principally from the standpoint of energy balance. The basic assumption was that all animals, including dogs, eat to meet their energy (caloric) needs first. However, in recent years this premise has been challenged. There is evidence that a wide range of species, including many birds, fish, and mammals, will self-select diets containing consistent proportions of the three major macronutrients – protein, fat and carbohydrate, and that they regulate and balance their nutrient intake to maximize lifespan and reproductive fitness. The recognition that macronutrient selection can be a driver for appropriate diet selection has led to several new studies with dogs and cats.

Domestic cats were studied before dogs and were found to consistently select a diet that was high in protein and fat and low in carbohydrate (5). This profile is consistent with that of other obligate carnivores and with the cat’s wild feline cousins. Interestingly, a very recent study with cats found that cats preferentially balanced their diets to a set protein:fat ratio, even when offered foods of different flavor preferences and containing animal- or plant-based protein sources (6). Although flavor and smell were important influences, the strongest factor for food selection appeared to be the total amount of protein in the food, rather than its source.

To date, only two controlled studies have been completed with dogs. In both, dogs have also demonstrated a similar talent to their feline friends for self-selecting the macronutrient content of their diets (7,8). The studies were conducted by different research teams and used somewhat different methodologies, but both reported that dogs preferentially selected diets that were low in carbohydrate, and high in fat and protein. When expressed as a percent of energy, dogs gravitated to a general distribution of 30 to 38 percent protein, 59 to 63 percent fat and 3 to 7 percent carbohydrate. Interestingly, wolves self-select diets that are even lower in carbohydrate –  only about 1 percent. Initially, the dogs in these studies were attracted to very high fat diets, but over a period of several days reduced the proportion of fat and moderately increase protein. An important finding of the most recent study was that when dogs were allowed to choose these dietary proportions over a period of 10 days, they tended to over-consume calories. On average, the dogs gained almost 3.5 pounds in just 10 days of feeding.

Its Complicated: At this point in time, we know that dogs can better digest starch in their diet compared with their wolf ancestors (and with present-day wolves). This increased capability is at least partially due to increased production of pancreatic amylase. We also know that, like us, dogs digest cooked starches very efficiently, but cannot utilize raw starch. We also know that the  inclusion of at least some level of starch in a dog’s diet provides an efficient source of energy (calories). Finally, most recently, we have learned that when given the choice, dogs preferentially select a diet that is low in starch, and that is high in protein and fat. However, self-selection of this type of diet (if fed without portion control) may lead to overconsumption and weight gain.

Still, none of this information provides evidence for the healthfulness of a diet containing some starch versus a diet that contains very low (or no) starch in terms of dog’s vitality, ability to maintain a healthy body weight and condition, development of chronic health problems and longevity. Unfortunately, this has not stopped proponents of low carbohydrate or carbohydrate-free diets from making such claims. The fact that dogs gravitate to a diet that is high in protein and fat and low in starch  is not to be confused with evidence that such a diet has been proven to be healthier or is capable of preventing illness. We simply do not know.

What we need at this point, is evidence of whether or not dietary carbohydrate is harmful, beneficial or, well,  neither. Dogs are generalists after all. It is quite possible that they, like many animals, are capable of thriving on a wide variety of diet types, including those with some level of starch.

Like I said. Its complicated.

Cited References:

  1. Axelsson E, Ratnakumar A, Arendt ML, et al. The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature 2013; 495:360-364.
  2. Arendt M, Fall, T, Lindblad-Toh K, Axelsson E. Amylase activity is associated with AMY2B copy numbers in dogs: Implications for dog domestication, diet and diabetes. Animal Genetics 2014; 45:716-722.
  3. Arendt M, Cairns KM, Ballard JWO, Savolainen P, Axelsson eE. Diet adaptation in dogs reflects spread of prehistoric agriculture. Heredity 2016; 117:301-396.
  4. Reiter T, Jagoda E, Capellini TD. Dietary variation and evolution of gene copy number among dog breeds. PLOSone 2016; 11:e01148899.
  5. Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, et al. Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus. Journal of Experimental Biology 2011; 214:1039-1051.
  6. Hewson-Hughes AK, Colyer A, Simpson SJ, Raubenheimer D. Balancing macronutrient intake in a mammalian carnivore: disentangling the influences of flavor and nutrition. Royal Society of Open Science 2016; 3:160081.
  7. Hewson-Hughes AK, Hewson-Hughes VL, Colyer A, et al. Geometric analysis of macronutrient selection in breeds of the domestic dog, Canis lupus familiaris. Behavioral Ecology 2013; 24:293-304.
  8. Roberts MT, BErmingham EN, Cave NJ, Young W, McKenzie CM, Thomas DG. Macronutrient intake of dogs, self-selecting diets varying in composition offered ad libitum. Journal of Animal Physiology and Nutrition 2018; 102:568-575.

A Taste for Meat?

The issue of how to classify the dog and how to best feed dogs continues to be a highly controversial topic among dog people. If you doubt this, just try posting this statement in a dog feeding chat group:

Dogs are omnivores and can thrive on a wide range of diet types.

Good luck surviving the night.

I discuss the current science regarding the dog’s classification in “Dog Food Logic” and in the Science Dog essay “Dogs are Carnivores, Right?“. (Spoiler alert: Dogs are omnivores). Regardless of what the science tells us, there is continued belief in statements such as these:

Dogs are obligate carnivores” [sorry, not];

“Dogs require meat in their diet” [no again]; and

Dogs naturally crave the taste of meat” [okay……this one may have some legs].

Anyone who lives with and trains dogs is aware that dogs are almost universally attracted to meaty foods and treats. Trainers use these preferences to select different levels of “treat value” for dogs and almost invariably, the treats that are of highest value to a dog are those that have a meaty texture, smell and (we assume) taste. It is also true that most dogs are highly attracted to and readily consume high protein diets that include cooked, extruded or raw meat of various types. So, are these preferences a reflection of the dog’s predatory past (wolf ancestors)? If so, are  such preferences something that dogs are born with or is there a strong influence of learning and environment on our dogs’ apparent “taste for meat“?

A recent set of experiments conducted by researchers who study free-ranging dogs in India asked these questions and provide us with some new information.

The Diet of Free-Ranging Dogs: Free-ranging dogs exist in numerous countries around the world, including Mexico, Italy, Nepal, Japan, many African countries, and India. They survive almost entirely by scavenging and occasionally augment their diet by begging and hunting small animals. In India, the history of free-ranging dogs is well-documented, extending back to the 9th century BC and representing more than 1000 generations of dogs.

FREE-RANGING DOGS SCAVENGING GARBAGE

Indian free-ranging dogs consume a diet that is rich in carbohydrate (biscuits, bread, rice) and relatively low in protein. The protein that is consumed is in the form of scraps of meat or fish adhering to bones, decomposing meat, and the remains of carcasses.  Domestic dogs are better adapted to scavenging and a diet that is higher in carbohydrate foods than were their wolf-like ancestors because of changes in foraging behavior (increased scavenging/decreased pack hunting) and enhanced ability to digest starch (increased copies of the gene AMY2B, the gene that codes for pancreatic amylase). However, just because dogs can consume and digest diets that contain a high proportion of carbohydrate (starches), it does not necessarily follow that they prefer such diets or that it is the healthiest or best way to feed them.

Although there are multiple questions here, the two that the Indian researchers attempted to answer were: “Do dogs have a strong preference for meat in their diet?” and if so, is such a preference innate (i.e. puppies are born with this preference) or is it reliant upon or strongly influenced by learning?

Do free-ranging dogs show a preference for meat? In the first study, the researchers offered 30 free-ranging dogs a variety of food choices in four separate experiments. In the first, dogs chose between bread, bread soaked in water, and bread soaked in chicken broth. They selected between bread, bread soaked in gravy, and cooked chicken in the second experiment. The third offered the dogs choices between dry dog kibble or bread soaked in varying concentrations of chicken broth. The final experiment offered the dogs varying combinations of bread and dog food kibble, soaked with different concentrations of chicken broth. The purpose of this final set of choices was to separate the factors of meat smell from nutrient (protein) content, because dogs have been previously shown to be capable of self-selecting a diet according to its macronutrient (protein/fat/carbohydrate) content (3,4 [more about these studies soon]).

Results: The following preferences were found in the adult, free-ranging dogs:

  • Meat (smell) beats carbs: The dogs consistently chose bread soaked in chicken broth over dry bread or bread soaked in water, even though chicken broth contains only a small amount of actual protein. They also selected chicken meat first over chicken-soaked bread or dry bread, when allowed to choose visually.
  • Smell beats all: When the dogs were offered kibble (high protein food) or bread (low protein food) soaked with varying concentrations of chicken broth, they consumed all of the foods equally, showing no absolute preference in terms of the quantity that was consumed. However, the order of selection depended completely upon how much chicken broth was soaking the food, regardless of its nutrient content. In other words, the dogs chose according to smell, not in accordance with the actual amount of meat protein present in the food.
  • “Rule of Thumb”: The cumulative results of the four experiments support the existence of the following rule of thumb for food choice: “Choose the food that smells the most intensely of meat first.” This means that the dogs preferred foods that smelled of meat (but that were not necessarily good sources of protein) over those that smelled less meaty, even when the less meaty smelling foods actually contained more meat ingredients and a higher protein content. This of course, makes sense, since in nature, a stronger meat smell is highly correlated with high meat and protein content and invariably predicts higher meat quantity. This relationship only becomes skewed when clever experimenters enter the picture and mess with it.

The authors conclude that while domestic dogs have adapted a scavenging lifestyle, they appear to have done so without giving up a strong preference for meat. They suggest that while the domestic dog has indeed evolved to more efficiently digest carbohydrate and exist on a carbohydrate-rich scavenged diet, they continue to be strongly attracted to the smell of meat and preferentially select meat-smelling foods. (Not surprising at all to most dog owners; but again, good to have science backing up experiences and beliefs).

But wait, they are not finished. The same researchers then asked……”So, are domestic dogs born with this preference for meat or is it a learned trait?” Using a clever design, they found out:

The Study: The researchers conducted the same series of the experiments described above with the puppies of free-ranging dogs.  The puppies were 8 to 10 weeks of age at the time of testing.

Results: Here is what they found:

  • Puppies did not discriminate: Unlike the adult dogs, puppies near weaning age showed no clear preference for foods that smelled strongly of meat and chose each food selection equally, regardless of how intensely it smelled of meat.
  • Sniff and snatch strategy: While the adult dogs tended to first inspect (smell) all available food choices before choosing and consuming one, puppies did not show this behavior. Rather, they would smell a food, eat it and then move to the next food, showing little to no preference. The vast majority (89 %) of choices made by puppies followed this behavior pattern.

The authors speculate that because puppies consume a protein-rich diet in the form of their mother’s milk, there is little selective pressure for an innate selection bias towards the smell of meat. It is only after weaning, when pups begin to scavenge, that preferentially selecting foods that smell like meat (and are correlated with a high protein content) becomes important. They suggest that, as has been shown in a number of other species, puppies learn their food selection preferences from the mother (i.e. cultural transmission of knowledge) and then as they mature and begin to scavenge, operantly.

Take Away for Dog Folks: The first study’s results with adult, free-ranging dogs tell us that the dogs in this set of experiments were selecting foods based primarily on smell rather than an ability to discern actual meat content. The adult dogs were operating under the (pretty efficient) rule of “If it smells like meat, eat it” (We all know and love dogs who do this…..). This strategy is probably strongly selected for in an environment in which resources are limited, there are few energy and protein-dense foods available, and competition between dogs is high.  This is not really a surprising result – except for the fact that the authors found that the scent of meat was more important than the actual meat (or protein) content of the food. Newly weaned puppies, on the other hand, lack this choice bias and appear to learn to choose “meaty” foods after weaning, either from the food choices of their mother, operantly, or most likely, a combination of the two.

So, what does this tell us about feeding our own dogs? Well, perhaps most importantly for all of you who enjoy a good internet scuffle, these results suggest that while dogs are predisposed to enjoy the taste of meat ingredients and clearly prefer these foods, puppies do not appear to be born with an attraction to the smell of meat per se and these preferences are influenced by learning early in life. On a practical level, these data, along with those of earlier studies of taste preferences in dogs and other species, tell us that the foods that are offered to a puppy at a young age should be expected to strongly influence the pup’s food and taste preferences as an adult dog.

Cited Studies:

  1. Bhadra A, Bhattacharjee D, Paul M and Ghadra A. The meat of the matter: A thumb rule for scavenging dogs. Ethology, Ecology and Evolution 2016; 28:427-440.
  2. Bhadra A and Bhadra A. Preference for meat is not innate in dogs. Journal of Ethology 2014; 32:15-22.
  3. Hewson-Hughes AK, Hewson-Hughes VL, Colyer A, Miller AT, McGrane SJ, et al. Geometric analysis of macronutrient selection in breeds of the domestic dog, Canis lupus familiarisBehavioral Ecology 2012; 24:293-304.
  4. Roberts MT, Bermingham EN, Cave NJ, Young W, McKenzie CM and Thomas DG. Macronutrient intake of dogs, self-selecting diets varying in composition offered ad libitum. Journal of Animal Physiology and Nutrition

If you enjoy reading The Science Dog, take a peak at Linda Cases’ newest book, “Dog Smart: Evidence-based Training with The Science Dog“!

Digestibility Matters

In  “Dog Food Logic” and “Only Have Eyes for You“, I have emphasized (okay, some might say “harped upon”) the need for pet food companies to provide digestibility information to consumers. It is not a difficult value to determine and most pet food companies already conduct feeding trials that measure this (yet keep the results to themselves). As one of the most basic measures of food quality, digestibility provides essential information that can help dog owners to select the best food for their dog.

What is digestibility (and why does it matter)? To refresh, digestibility reflects a food’s ability to deliver essential nutrients to the dog who is eating it. This ultimately affects not only defecation quantity and quality (how much your dog poops and how the poop looks and smells), and a dog’s propensity for flatulence (no explanation needed), but more importantly, a dog’s longterm health and wellness. This graphic, presented in the essay, “Scoopin’ for Science“, summarizes how digestibility is measured using feeding trials with dogs.

Digest Trials

In case you have not noticed, it is that last step, “Provide Results to Consumers” that is glaringly absent from the dog food scene. But, I harp (again).

Onward. There is good news to tell.

Good vs. Poor Digestibility: The term digestibility coefficient refers to the percent of a food that the dog absorbs into his or her body during the process of digestion. As a rule of thumb, dry dog foods with digestibility values of 75 % or less will be of very poor quality, those with values between 75 and 82 % are classified as moderate in quality, and foods with digestibility values that are higher than 82 % are of high quality. If you see products with 88 % or more reported digestibility, you have a rock star.  (For a more detailed explanation of dog food digestibility, see “Dog Food Logic“).

The paradox lies in the fact that while many pet food companies routinely measure the digestibility of their products, they are not required to report this information to the people who buy their foods. Most do not provide this information even when it is directly requested. Digestibility matters (a lot), but we cannot judge foods with information that we do not have.

The good news is that two research studies measuring the digestibility of dog foods formulated with different types of protein sources were recently published by a group of animal nutritionists from the Norwegian University of Life Sciences and the University of Copenhagen in Denmark (1,2). The first compared the digestibility of dog foods that used three common animal protein meals and the second compared the use of fresh chicken meat (aka “chicken first”) with poultry meal as protein sources in a dry food. Because all of the protein ingredients that the researchers examined are frequently found in commercial foods, their results may be helpful to you in your search for a quality food.

Like me, you may be surprised by what they found:

Lamb, fish, or poultry meal? In the first study, the investigators compared the protein and overall digestibility of three dry (extruded) dog foods that were formulated containing equivalent amounts of either lamb meal, fish meal or poultry meal (1). Because one of the objectives of their work was to determine if mink provide a suitable model for assessing pet food quality, they tested the foods in growing mink, adult mink and adult dogs.

Results: As a protein source, lamb meal showed significantly lower values for multiple measures of protein quality and essential amino acid content when compared with both poultry meal and fish meal. Even though all three diets were formulated to provide complete and balanced nutrition, the lamb meal diet was found to be deficient in the essential amino acid methionine, when digestibility was taken into account. Although differences between poultry and fish meals were not as dramatic, poultry meal was of lower quality than fish meal. As a protein source in dog food, fish meal had the highest values on almost all quality measures, including digestibility and essential amino acid content. When tested in adult dogs, the protein digestibility values of the three foods were 71.5, 80.2, and 87.0 for lamb meal, poultry meal and fish meal, respectively. Overall, this study suggests that, at least for the sources used in this work, the order of protein quality was lamb meal (poor), poultry meal (moderate), and fish meal (high). Additionally, although the reported level of lamb meal in the diet exceeded the minimum methionine requirement for adult dogs, the actual amount of methionine that was available to the dogs (i.e. was digested) was less than their minimum requirement for this nutrient.

lamb-meal-vs-poultry-vs-fish

LAMB MEAL IS SIGNIFICANTLY LOWER IN DIGESTIBILITY THAN POULTRY MEAL AND FISH MEAL WHEN INCLUDED IN AN EXTRUDED DRY DOG FOOD

Is fresh chicken better? The team’s second study is groundbreaking. It is the first to examine whether or not there is a demonstrated benefit to including “fresh” (frozen, actually) chicken in an extruded, dry dog food. This is important because the promotion of “fresh first” on pet food labels is frequently used as a claim for higher protein quality in the product. The researchers tested the digestibility and amino acid content of fresh, raw chicken (technically referred to as “raw mechanically separated chicken meat”) before processing (cooking) and then again after it was included in a dry dog food to replace about 25 percent of the product’s poultry meal. Because raw meat has been shown to be more digestible than dry rendered protein meals, it was hypothesized that including raw chicken in the dry food would indeed improve the foods digestibility by several percentage points. (Note: Because mink had been previously shown to be a suitable model for dogs, adult mink were used to test the diets).

Results:  As expected, when tested before processing the digestibility of raw chicken meat was significantly higher than that of rendered poultry meal (88.2 % vs. 80.9 %, respectively). However, when the raw chicken meat replaced 25 percent of the poultry meal in an extruded dry food, the digestibility of the food was not significantly improved  (81.3 vs. 80.3, respectively).  In addition, the digestibility of several essential amino acids was actually higher in the food containing only poultry meal than in the food that included the raw chicken meat.

chicken-not-better-than-poultry-meal

WHEN INCLUDED IN A DOG FOOD, FRESH (RAW) CHICKEN MEAT DOES NOT IMPROVE THE FOOD’S PROTEIN DIGESTIBILITY OR AMINO ACID AVAILABILITY COMPARED WITH POULTRY MEAL

Take Away for Dog Folks

Wow. The results of these two studies contradict several previously accepted (if never actually proven) dog food edicts. These are:

  1. Lamb meal is a high quality protein source for pet foods. Um, apparently not. The first study found that lamb meal was poorly digested (70.5 %) and provided inadequate levels of an essential amino acid, methionine after digestibility was taken into account.
  2. Named species meals are always superior to generic meals. This refers to the general rule of thumb that dog folks should always choose a food that uses chicken, turkey, salmon or lamb meals over the less specific meat, poultry or fish meals. At least regarding the animal-based protein sources used in these studies, choosing lamb over the generic poultry or fish may not get you the quality you are hoping for.
  3. Chicken first on the pet food label means higher quality (more digestible) protein: Nope again. While the digestibility of fresh chicken meat was higher than that of poultry meal when tested prior to processing, incorporating fresh chicken (as 25 percent of the protein source!) into an extruded food did not improve digestibility or lead to a higher quality product. The researchers speculated that this may have occurred because raw meat ingredients could be more susceptible to damage caused by the heating and drying processes of extrusion than are rendered protein meals. Regardless of the cause, it appears that “Chicken First’ may not be the marketing holy grail that pet food companies are promoting it to be.
soapbox

UP ON MY SOAP BOX

This is great information for dog folks to have. Many thanks to this team of researchers, among others (all notably at universities, not from pet food companies) who have been publishing scientific evidence regarding the protein quality, amino acid content, digestibility and safety of various dog food ingredients and products. We are grateful to you all and hope to see more of these types of studies. Although these do not (yet) go so far as to provide us answers to the most important question: “What is the digestibility of the  brand of food that I am feeding to my dog?” they provide needed and essential information.

I have said this many times before and will say it again:

If pet food manufacturers insist on telling us that their brands of food are expected to provide “complete and balanced nutrition” throughout our dogs’ lives, then providing a few very simple measures of the quality of those foods is not too much to ask.

The researchers of these papers agree. They finish the abstract of their first paper with this statement: “Furthermore, the study showed that to ensure nutritional adequacy of dog food and to be able to compare protein quality of dog foods, information of AA [amino acid] composition and digestibility is crucial“. [Emphasis mine].

So, pet food manufacturers……..are you listening? Time to step up and provide this information on your labels, websites, or at the very least, in response to direct inquiries.  In the meantime, I will continue to report and promote research studies that provide us with the information that we need to choose smart for our dogs.

Until next time, happy feeding and happy training!

Chip and His Cake

CHIPPY WONDERS ABOUT THE DIGESTIBILITY VALUES OF HIS CAKE

Cited Studies:

  1. Tjernsbekk MT, Tauson AH, Matthiesen Cf, Ahlostrom O. Protein and amino acid bioavailability of extruded dog food with protein meals of different quality using growing mink (Neovison vison) as a model. Journal of Animal Science 2016; 94:3796-3804.
  2. Tjernsbekk MT, TAuson AH, Kraugerus OF, Ahlstrom O. Raw, mechanically separated chicken meat and salmon protein hydrolysate as protein sources in extruded dog food: Effect on protein and amino acid digestibility. Animal Physiology and Animal Nutrition 2017 (in press).

 

“Only Have Eyes for You: Exploring Canine Research with The Science Dog” – Kindle Edition Now Available!

The Kindle edition of Only Have Eyes for You: Exploring Canine Research with The Science Dog” is now available! Click on the image below for more information and to order.

Book description:  In her second Science Dog book, Linda Case tackles commonly held beliefs about canine nutrition, pet foods, behavior, social cognition and training. Each of the book’s 32 chapters explores a current issue that is of interest to dog owners and pet professionals and presents the scientific evidence that supports or refutes commonly held claims and beliefs. Learn about pet food ingredients and research showing that what is on the label may not always be in the food, about measures of food quality (and what consumers may not know about the foods that they buy), and about the safety and digestibility of popular dog treats and chews. Other chapters review new information regarding how dogs communicate, factors that help or inhibit a dog’s ability to learn, and the effectiveness of different types of training. Find out if dogs are capable of “knowing what someone else knows”, if they feel empathy for their friends, if they bark for no reason, and if they are capable of feeling guilt following a misdeed. Learn more about breed stereotyping, factors that influence our perceptions of dogs, and which canine characteristics most influence our attraction to particular dogs. This newest Science Dog book has something for everyone who works with and trains dogs, as well as for those who simply love dogs and enjoy learning more about our canine best friends.

                                                                             ♥♥♥♥♥♥♥♥♥♥♥♥♥♥

coversnip

New Book! “Only Have Eyes for You: Exploring Canine Research with The Science Dog”

Only Have Eyes for You: Exploring Canine Research with The Science Dog” (paperback version) is now available! Click on the image below for more information and to order. (Kindle version will be available soon!)

Book description:  In her second Science Dog book, Linda Case tackles commonly held beliefs about canine nutrition, pet foods, behavior, social cognition and training. Each of the book’s 32 chapters explores a current issue that is of interest to dog owners and pet professionals and presents the scientific evidence that supports or refutes commonly held claims and beliefs. Learn about pet food ingredients and research showing that what is on the label may not always be in the food, about measures of food quality (and what consumers may not know about the foods that they buy), and about the safety and digestibility of popular dog treats and chews. Other chapters review new information regarding how dogs communicate, factors that help or inhibit a dog’s ability to learn, and the effectiveness of different types of training. Find out if dogs are capable of “knowing what someone else knows”, if they feel empathy for their friends, if they bark for no reason, and if they are capable of feeling guilt following a misdeed. Learn more about breed stereotyping, factors that influence our perceptions of dogs, and which canine characteristics most influence our attraction to particular dogs. This newest Science Dog book has something for everyone who works with and trains dogs, as well as for those who simply love dogs and enjoy learning more about our canine best friends.

                                                                             ♥♥♥♥♥♥♥♥♥♥♥♥♥♥

coversnip

What’s in Your (Vegetarian) Food?

Here we go again.

It appears that there may be more than what dog owners expect to find in vegetarian dog food.

Hold the Spam, Please: Before all of the  “Dogs are Carnivores (and a pox on your mother if you think differently)” devotees begin posting comments (in all caps ) that dogs should NOT be fed a vegetarian diet in the first place, let me state that this is not what this blog piece is about. So please, don’t even start. The point of this essay is not to argue (again…..) whether or not dogs have an absolute requirement for meat in their diet (here’s a hint: They don’t). Rather, today we examine new information about undeclared ingredients that may be present in dog food and the mounting evidence of regulatory violations within the pet food industry.

In this newest pair of studies, a team of veterinary nutritionists at the University of California tested vegetarian pet foods for label compliance and ingredient content.  I have written about this before, and unfortunately once again, the news isn’t good.

25-Foods-That-Seem-Vegetarian-But-Arent

Label Compliance: In the first study, the researchers collected samples of 24 dog and cat food brands that carried a label claim of “vegetarian” (1). The majority of the foods were over-the-counter products purchased at a local pet supply store. Three products were veterinary therapeutic diets. Of the group of products, 19 were formulated for dogs or for dogs and cats, and five were formulated exclusively for cats.  Product labels were examined for their compliance with the Association of American Feed Control Official (AAFCO) model regulations, which are the basis for most state mandated pet food regulations. Pet food samples were also analyzed for total protein and essential amino acid content. Results: Of the 24 foods, only eight (33 %) were in complete compliance with AAFCO label regulations. This means that 16 brands (66 %) had one or more violations. The most common infractions were the omission of feeding instructions or caloric content, improperly reported guaranteed analysis panels, and mislabeled ingredient statements. Nutrient analysis showed that all but one of the foods met AAFCO’s minimum crude protein requirements. However, six brands had deficient levels of one or more of the essential amino acids. This means that while the total amount of protein that the food contained appeared to be sufficient, essential amino acid requirements, which are more important, were not always met.

Presence of Animal-Based Ingredients: In a second study, the same group of researchers tested 14 brands of vegetarian pet foods (2). They purchased each food on two occasions to obtain samples as duplicates from different manufacturing batches. Six were dry and eight were canned products. Samples were analyzed for the presence of mammalian DNA using an accepted laboratory technique called multiplex polymerase chain reaction (PCR). Since all 24 foods were marketed as vegetarian (and in some cases, as vegan), none included animal-based components in their list of ingredients. Results: All six of the dry (extruded) foods that were tested contained DNA from beef, pork or sheep and five of the six contained DNA from multiple animal species. These results were consistent across batches for all 7 products.  Only one of the 8 canned vegetarian foods contained animal DNA (beef) and this finding was not repeated in the second sample. In this study, the researchers also tested for the DNA of dogs, cats, goats, deer, horses, rats, mice and rabbits. DNA from these species was not detected in any of the samples. Similar to earlier studies that have found the DNA of undeclared meats in dog foods, the amount of animal-based ingredients in the foods could not be quantified. The researchers could not speculate whether the labeling violations were a result of deliberate adulteration or unintentional cross-contamination of vegetarian products with meat-containing foods produced at the same facility.

soapbox

Soap Box Time: The Federal Food, Drug and Cosmetic Act requires that all pet foods sold in the United States are safe, produced under sanitary conditions, contain no harmful substances, and are truthfully labeled (emphasis mine). Perhaps I am being picky, but labeling a food as vegetarian and then not ensuring that the food indeed lacks the meat of cows, pigs and sheep, seems to qualify as not being truthful. (Some might even call it lying, I suppose). Not only are such egregious errors in violation of both FDA and AAFCO regulations, but they seriously impact the trust that dog owners have in pet food manufacturers. And rightly so.

To date, the majority of pet owners in the US continue to feed dry, extruded food. Of the dry-type vegetarian foods tested in this study, all of them, 100 % were, in fact, not vegetarian at all. This leads one to ponder about other products on the market and whether it is more the norm than the exception for dry dog foods that are sold as vegetarian to be nothing of the sort. While the authors note that this was a small number of products and so do not represent all vegetarian foods, the fact that all of the foods failed their DNA tests is alarming.

What can you do as a dog owner? Contact the manufacturer of your food and ask them how they verify the integrity of their products, specifically, the ingredients that they include in their foods. If they are not forthcoming and transparent with their response, find another producer who is. The good news is that the pressure that research studies such as these place on pet food companies and upon the industry as a whole will hopefully encourage increased transparency and improved regulatory oversight – something that we are apparently in dire need of.

Cited Studies:

  1. Kanakubo K, Fascetti AJ, Larsen JA. Assessment of protein and amino acid concentrations and labeling adequacy of commercial vegetarian diets formulated for dogs and cats. Journal of the American Veterinary Medical Association 2015; 247:385-392.
  2. Kanakubo, K, Fascetti AJ, Larsen JA. Determination of mammalian deoxyribonucleic acid (DNA) in commercial vegetarian and vegan diets for dogs and cats. Animal Physiology and Animal Nutrition 2016;  doi: 10.1111/jpn.12506.