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“!

13 thoughts on “A Taste for Meat?

  1. The street and owned, free-ranging dogs in Maun, Botswana also raid garbage for an omnivorous diet, but you should see them when they get their teeth into a road-killed donkey – there is no question that they like raw, bloody meat.

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  2. I’ve always wondered whether dog food manufacturers aimed product scents at attracting the dogs or the people feeding the dogs. Another topic I’d love for you to take up some time: TASTE. Since dogs’ olfactory capabilities are exponentially stronger than ours, does that mean that their sense of taste is similarly enhanced?
    \

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    • Hi Linda, Thanks for your note and comment. We do know that dogs (and cats) have taste (gustation) systems that follow the same pattern as many meat-eating mammals. Specifically, their taste receptor cells (found in the “taste buds”) have concentrated numbers of receptors that respond to amino acids and nucleotides (protein, meaty flavors) and lack a strong preference for salty flavors. Dogs, but not cats, show a preference also for sweet flavors (which suggests again, a more omnivorous – meat and fruits/veggies dietary history in dogs but not cats). I will keep an eye out for recent studies of taste perceptions and selection as I too would like to learn more about this! Thanks for the suggestion and for reading! Best, Linda

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  3. Interesting!

    “…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.”

    My feral puppy, Clara, arrived at my house probably a week or two after she was weaned. As it happened, the first thing I offered her was fake cheese in a spray can. (All the purists can jump on me now.)

    I have often said it was what tamed her. And it remains her highest value food to this day.

    Eileen Anderson

    Liked by 1 person

    • Hi Eileen! So interesting about Clara. I knew that she was your feral pup, but did not know the story about your use of spray cheese with her. It is truly wonderful to see her in your training videos and so heartwarming to know how far she has come. Regarding early experiences and later food preferences: There are actually a number of studies in dogs and cats showing that early experiences with both food flavors and textures have a strong influence on adult food preferences. In cats, these can actually lead to “fixed food preferences” that are often difficult to alter. (Dogs, as always, are a bit more flexible in their preferences, again demonstrating their more generalist nature compared with the more specialist nature of the cat). What I found interesting about this particular set of studies were the results suggesting that an interest in meaty flavors/smells was not innate – at least not by 8 to 10 weeks (see discussion below). Like most behaviors though, I would suspect that there is both a genetic predisposition (genetic preparedness) for an attraction to meat flavors in dogs that is then triggered or augmented by learning. Cool stuff, either way! Linda

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    • When my 8 week old puppy had her leg broken in a dog attack, her pain level was so high she had no appetite! Except for.. Mac and cheese. So I ended up mixing some of that into her kibble to get her to keep something down (pain reduced significantly and appetite improved after ortho surgery to stabilize break in humerus) To this day Zia’s favorite food is mac and cheese.

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  4. It might be true that puppies learn their meat smell preference from their mother. But as far as I can tell, this study doesn’t support that. Sure they aren’t born with it. But it might be innate in another sense: it’s a timed developmental stage, ie it’s turned on at a certain point in their development automatically or in response to certain environmental stimuli, rather than learned.

    Liked by 1 person

    • Hi David – A good point. These data suggest that, at least by 8 to 10 weeks of age, an innate preference for meat flavor has not expressed itself. This definitely (and I would suggest, even probably) could develop with age in the form of preparedness – I.e. an attraction to meaty flavors is very readily learned given the opportunity to eat meat. This seems likely since there are very few behaviors that we find do not have both a genetic component and a learned component, though the degree of impact of each certainly varies. As I said above to Eileen, what I found fascinating about these results was that the pups had very little food discrimination skill and showed a lack of preference for meaty scents – I would not have expected this and was surprised by it. Certainly, it would be interesting to study whether or not such preferences begin to express themselves in later weeks of life, in the absence of learning. Thanks for your note! Linda

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  5. I have a couple of observations to make.
    Firstly these dogs are street dogs. What else will they eat but what they scavenge? If you studied modern day wolves in the wild or African wild dog packs you’d get a totally different result. If you put a pack of feral dogs (Canis lupus familiaris) in a remote location and some survived, they would do so on whatever was available. As the study makes clear these dogs will hunt but scavenging from human waste is easier. The available waste food is not high in protein because we value it more highly and don’t throw it away lightly, so again they are eating what we leave them – waste carbohydrates such as bread and rice which are more abundant.
    Surely what a dog is, is not defined by what it eats in an unnatural environment but by its biology? Canis lupus familiaris is a carnivore which has learned that humans are the source of rich and varied easy pickings and hence developed some ability to digest what is/was most common in our rubbish tips – that is why the species C lupus familiaris diverged from the shared wolf ancestor. (Incidentally full speciation only occurs when inter-breeding is no longer possible doesn’t it? And as that’s not yet happened, they are not yet evolved fully away from their nearest cousins but that’s a different and speculative discussion perhaps.)
    The dog food companies are well aware of the scent issue – this is what digest was invented for, to make largely vegetable protein and carbohydrate smell like more expensive meat. It is applied to dry dog food post-extrusion to make a kind of meaty cheerio out of waste and by-products from human food production.
    If we follow the suggested logic then we could now argue that humans in the developed western parts of the world are evolved to eat the high carb and high sugar diets that are so bad for us. It’s what’s available in abundance and we choose it by preference because of some basic biological imperatives that drive us to consume high calorie food whilst it is available to store it up for times when food is scarce even though we (the lucky ones) are now living in a world where the chance of famine is vanishingly small.
    What we eat and what we are in a fundamentally biological way designed to thrive on are two very different things. Just like us dogs no longer control what they eat – something they gave up for the convenience of not having to hunt or find their own food – just as humans are centralising and industrialising their food production and supply. Whether these environmental levers on both species (us and the dogs we keep) prove beneficial in the long term and bring health and success at a species level has yet to be seen (both for dogs and humans) but all the signs are that declining health and wellbeing are more likely. Sadly I think the dog may have put its faith in the wrong species when it comes to making good food choices.

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  6. I really enjoyed reading about this study, especially the section on puppies and their preferences (or lack thereof). Thank you for sharing this.

    Liked by 1 person

    • Hi Christine, Thanks. This is a good point, but most of the evidence that I have seen has shown that the olfactory system of puppies is well-developed very early in life, so I am not sure that this would be a strong explanation. Plus, the pups did sniff the foods first, but then immediately ate whatever they came upon. Thanks for your note! Linda

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