Why petfood palatability is species-specific. A cat is not a small dog in the liver, where a drug tolerated by one species can be dangerous to the other. This essay asks whether we have remembered that at the bowl.
There is a tablet in almost every home that makes the point rather brutally. Paracetamol is a familiar medicine for people, and can be used therapeutically in dogs under veterinary supervision. In cats, the same molecule can be dangerously toxic. The difference is not in the tablet. It is in the animal receiving it.
Veterinary medicine learned this a long time ago. Species is not a matter of scale. A cat is not a dog made smaller, any more than a dog is a wolf brought indoors and shrunk to fit the sofa. Their biology diverges in places that matter, and what one species can metabolise, tolerate or use safely cannot simply be carried across to the other. A cat's liver, in this instance, lacks the machinery a dog's relies on to break the drug down and clear it, so what leaves one animal quietly builds up in the other. We accept the lesson readily when the consequence is toxicity.
At the bowl, we have sometimes been less careful.
A cat and a dog can be offered the same food, carrying the same volatile compounds, the same peptides and amino acids and nucleotides and fats. On the analysis sheet the stimulus is identical. Biologically it is not, because it arrives at two different sensory systems, shaped by two different evolutionary histories, equipped with different receptors, different feeding behaviours and different expectations of what a meal is supposed to signal. The formulation may be identical. The sensory information arriving at the brain is not.
So this Conversation begins with a proposition that veterinary medicine already knows by heart, and that petfood palatability has been slower to take seriously. A cat is not a big dog. Not in the liver, where the difference can be measured in survival. And, this essay will argue, not at the bowl either. Which leaves a question worth carrying through everything that follows: when a cat turns from a food that a dog accepts, what exactly have we learned, about the food, or about the difference between the two animals we offered it to?
Movement I
SAME BOWL, DIFFERENT ANIMAL
Start not with the senses but with the two histories that shaped them, because the difference between a cat and a dog at a bowl is older than either animal's tongue.
The dog descends from a pack hunter and scavenger, an animal that ate when it could and often could not, that pulled down large prey together and gorged, then went without. That past is written into the dog we feed, an animal broadly built to take a large meal quickly and to wait a long time for the next, tolerant of a bowl that arrives once or twice a day, and inclined to try what it finds, because a scavenger that samples widely eats more often than one that does not. The cat descends from something quite different, a solitary hunter of small prey, an animal that caught a mouse, ate it, and hunted again, many times across a day and a night. It was never a gorger, because a mouse is not a feast, and its body records the difference at the plainest level. A cat's stomach is small, holding only a few hundred millilitres, restricted enough that the natural pattern is many small meals rather than a few large ones. In the wild the cat takes something like a dozen or more tiny feeds across the day, five to seven grams at a time, little and often, the rhythm of the hunt.
The dog was built to gorge and wait. The cat was built to graze the day in small returns.
Hand these two animals the same bowl, on the same once-a-day schedule, in the same quantity, and something quietly odd has happened, though it is so ordinary we never notice it. We have asked the cat to eat like a dog. Much of what frustrates the owners of cats, the food left half-eaten and returned to through the day, the refusal of a large single serving, the picking and grazing that reads as fussiness, is the cat doing exactly what it was built to do at a bowl designed around the dog's pattern rather than its own. And the cat is warier of the new than the dog, because a specialist hunter of fresh prey is safer treating the unfamiliar with suspicion where a scavenger profits from trying whatever it finds. So it is worth asking, before we call the cat difficult, whether we have ever actually offered it a cat's meal, or only a dog's meal that a cat was expected to accept.
The difference runs deeper than schedule and quantity, down to what each animal is trying to achieve when it eats. Left to choose freely among foods, neither animal simply eats what tastes best. Each eats toward a target, a particular balance of protein and fat that suits its biology, and the two targets are not the same, the dog's leaning toward fat and the cat's toward protein, close to the composition of the prey it evolved to catch. The striking part is what happens when taste and target disagree. In studies where cats were offered foods of different flavours and different nutrient content, they chose at first by flavour, exactly as we would expect, and then, over the following days, learned the compositions and shifted their choices to reach their nutritional target, overriding the very flavours that had won the first meal. Read that slowly, because it unsettles a comfortable assumption. For the cat, in the end, palatability can lose to need. The tastiest option does not necessarily win if it pulls the animal away from where its body is trying to go, and that is not a fact one could ever recover from a single first-choice test.
It is worth conceding at once that the line is cleaner than nature is. A Chihuahua is not a Great Dane, and on several of these measures a tiny toy dog with a small stomach and a delicate appetite sits closer to a cat than to a mastiff that bolts a bucket of food and looks up for more. Breed, size, age and temperament all move an animal along these axes, and the within-species range can be as wide as the gap between species. The claim is not that every cat differs from every dog on every count. It is that the cat, as a type, is built along a different line from the dog, as a type, and that the differences are biological and consistent rather than matters of mood. So before we ask why the cat is harder to please, a prior question is worth holding: harder to please than what, and measured against whose idea of a meal?
Movement II
THEY DO NOT TASTE THE SAME WORLD
If the two animals were shaped by different pasts, the deepest mark that past has left is on the senses that meet the food, and here the differences are not of degree but of kind. Set the same bowl before a cat and a dog and, at the level of the nerves, two different foods are being received.
Begin with the plainest divergence, which is also the one most easily forgotten. The cat cannot taste sweetness. The receptor that detects sugars, which the dog carries and responds to, exists in the cat only as a broken gene, present in the genome but silent, switched off across evolutionary time in an animal that never ate anything sweet. This is not a mild preference against sweet things. It is an absence of the signal altogether, in the way a colour-blind eye receives nothing where another eye receives red. A sweet note that a dog leans toward reaches the cat as nothing at all. And it would be a mistake to fill that silence with our own vocabulary, because the risk throughout this territory is that we describe the animals' senses in the words of ours. Both cats and dogs respond to the savoury, meaty quality we call umami, but they do not reach it by the same route; the molecules that trigger it most strongly in a cat, abundant in fresh animal tissue, are not the same ones, or in the same proportions, that trigger it in a dog. The word is the same. The chemistry the word points to is not.
The formulation may be identical. The sensory information arriving at the brain is not.
If that is true of the one taste the two animals seem to share, what should we expect of a food built on the human assumption that savoury is savoury and sweet is a virtue, to whichever animal happens to eat it? The cat also judges with a strikingly small set of taste instruments, a few hundred taste buds where a dog has several times as many, and it would be easy and wrong to read that as a fainter version of the dog's palate. It is not weaker. It is narrower and more sharply tuned, an instrument built to make a small number of distinctions that matter to a hunter and to ignore much that does not. And because the palate gives it so little to work with, the cat throws the weight of the decision onto its nose. Even here the easy comparison misleads. The dog carries more scent receptors overall, and on that number alone one would call it the better-nosed animal, but the two noses are built for different jobs. The dog's is built to detect and to track, to find a faint scent across a field. The cat's is built to discriminate, to tell one close smell from another, and it carries several times as many of the specialised receptors that do that fine sorting. The dog's nose asks where is it. The cat's asks what exactly is it, and is it right. And because the cat can barely taste, that discriminating nose is not a helper to the meal decision. It is the meal decision.
The dog's nose is built to find the food. The cat's is built to judge it.
Then, if the food passes the nose, comes the mouth, and the cat's mouth is a set of prey tools the dog's is not. A dog's jaw can move sideways and grind; a cat's cannot. The feline jaw is close to a pure hinge, and the teeth behind it are blades, not millstones, shaped to shear meat from a carcass rather than to crush and chew. A cat has fewer teeth than a dog and none of the flat grinding surfaces, and so it does not really chew in the sense we mean; it slices and swallows, or rolls a piece to the side to break it. Even the tongue is a different tool, covered in backward-facing spines of keratin, the same material as the claws, a rasp built to strip meat from a bone where a dog's tongue is smooth. Salt, which flatters the human palate and is useful in the dog, is close to dead in the cat, an obligate carnivore that ate whole prey and was never short of sodium. At point after point, the same food is not the same food. It is warmed or cooled into a different aroma, met by a different palate, judged by a different nose, and handled by a different mouth. So the question that closes this movement is not whether cats and dogs differ. It is a harder one. How did we ever persuade ourselves that a signal built to please one of them would arrive, unchanged, at the other?
Movement III
THE PALATANT IS NOT THE MESSAGE
There is a way of speaking about palatability that treats it as a property a food simply has, a quality you can build into a recipe and then measure, the way you build in protein and then measure it. On that view a palatant is a thing you add to make a food more palatable, and palatability is what you have added. It is a comfortable picture, and it is wrong, and the two animals we have just been comparing are what expose it. Because here is the question the comparison forces. If the molecule leaving the bowl is the same, and the animal receiving it is not, where exactly does the palatability live?
Consider what a palatant actually is. It is a collection of signals, chemical and physical, aromas and tastes and textures, assembled to be detected. But a signal is not a message until something receives it, and detection is only half of what is happening at the bowl. The other half is interpretation, and interpretation belongs to the animal, not to the food. A molecule that lands on a receptor the cat does not have sends nothing. A molecule that lands on a receptor the cat has, but reads through the biology of a fresh-kill hunter, may mean something quite different to the cat than the same molecule means to the dog. The palatant does not carry its meaning inside it, sealed and portable, the way a number is carried on a specification sheet. Its meaning is made, each time, in the meeting between the signal and the animal that receives it. We said it of the drug at the start, and it holds just as firmly here. The difference is not, in the end, in the palatant. It is in the animal receiving the signal.
There is no such thing as a palatable molecule. There is a molecule, a receptor, an animal, and a response.
An earlier Conversation reached the same place from a different door. It argued that palatability does not reside in the food alone, that a diet is not palatable or unpalatable in the abstract but only to a particular animal, in a particular state, on a particular day. That was said of the individual patient, of how illness and appetite and memory change what a food means to the one animal in front of the bowl. This is the same truth read at the level of the species. If palatability does not reside in the food for a single sick cat, it does not reside in the food across the gulf between a cat and a dog either. It never lived in the molecule. It lives in the response, and the response is the animal's to give.
This is why the comfortable picture fails, and why it matters that it fails. If palatability were a property of the food, then a food made more palatable would be more palatable to whatever ate it, and the species of the eater would be a detail. But if palatability is a response, assembled freshly in each animal from signals its own biology decides how to read, then the species is not a detail at all. It is the thing that decides what the signals mean. So a food developed until it performs beautifully for one animal has been tuned, precisely, to one animal's way of reading it. What has it been tuned to, for the other? And how would we know, if the only animal we asked was the one it already suited?
Movement IV
ONE FACTORY, TWO BOWLS
None of this is news to the people who make pet food. Of course the industry develops separately for cats and dogs; of course it knows the two animals differ. The question is subtler, and it is about assumption rather than intent. When a discipline grows up around the easier subject, its habits form around that subject, and the habits travel quietly into the harder work without anyone deciding they should. The dog is the more forgiving eater, the one whose acceptance is simpler to win and simpler to read, and a great deal of what we know about testing food, about what a good result looks like and how to interpret a bowl, was learned where it was easiest to learn. The risk is not that we treat the cat as a dog on purpose. It is that a canine logic, built where the animal was accommodating, becomes the default logic, and is carried into feline work as though it were neutral.
Nowhere does this matter more than at the frontier the rest of this series keeps returning to, which is the replacement of familiar animal ingredients with new ones. When a formulator sets out to replace chicken with a protein from a fungus, an insect, a microbe or a plant, it is tempting to describe the task as swapping one protein for another. But a protein is never only a protein. It arrives with a whole constellation around it, a particular set of amino acids and peptides, of nucleotides and volatile compounds, of fats and physical characteristics, and that constellation is precisely what the animal's senses read. Change the source and you change the constellation, and you are no longer presenting the same message to be received. You are presenting a different one, to two different sensory systems, each of which will decide for itself what it means.
A protein is never only a protein. It is the whole constellation the senses read.
And here the species divide turns from a matter of biology into a matter of consequence. Suppose the new protein is tested and accepted by dogs, and performs well. That is a real result, and a welcome one. But when a palatant performs beautifully in dogs, what exactly have we learned about cats?
When a palatant performs beautifully in dogs, what have we learned about cats?
Less than we would like. The dog, with its broader tolerances, its functional sweet sense, its more forgiving nose and its scavenger's willingness, is the animal most likely to accept a substitution and least likely to notice what the substitution lost. A replacement that satisfies the dog has cleared the lower bar. Whether the same replacement has reconstructed, for the cat, the specific chemical world its narrow and exacting biology is tuned to detect, is a separate question, and the dog's acceptance does not answer it. This is why the palatability of alternative proteins is so easily underestimated. It looks like one problem, solved once the animals eat. It is at least two problems, and the one we are more likely to have solved is the one that was easier to begin with.
A replacement the dog accepts has cleared the lower bar. The cat's bar is a different question.
Step back, at the end, and look at the whole arrangement from the factory end of the chain. We put a cat and a dog under the same roof, call them both pets, formulate complete foods for both, coat those foods with things meant to make them desirable, and measure what disappears from the bowl. From that vantage it is natural to see two versions of a single problem, palatability, to be solved with one set of tools and confirmed with one kind of test. Evolution did not see two versions of one problem. It built two different animals, from two different pasts, reading the same bowl through two different sets of senses, wanting two different things from a meal and defending them in two different ways. A cat is not a small dog in the liver, where the wrong dose finds it out. It is not a small dog at the bowl either. And perhaps palatability, if it is to mean anything precise, has to begin not with the food, and not with the factory, but with the animal we are actually asking to eat.
References
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About the Author
Dr. rer. nat. habil. Dr. Seronei Chelulei Cheison is the founder and Chief Executive Officer of Sinonin Biotech GmbH, where he works with petfood companies on palatant sourcing strategies, the innovation of palatability enhancers, and the design of palatability assessment. A trained food enzymologist, he led alternative protein and palatant development at Mars Petcare before founding Sinonin, and his research on protein chemistry spans two decades, a doctorate from Jiangnan University, and a habilitation from the Technical University of Munich.
Sinonin Biotech GmbH is a partner in the ZEST project (Grant Agreement No. 101157382) and the PROSCALE project (Grant Agreement No. 101288362), both funded by the Circular Bio-based Europe Joint Undertaking (CBE JU) under the European Union's Horizon Europe research and innovation programme. Views and opinions expressed are those of the author only and do not necessarily reflect those of the European Union or CBE JU. Neither the European Union nor the granting authority can be held responsible for them.
