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Our wonderful life-supporting planet is home to a remarkably diverse and complex spectrum of
living organisms. And although all living things do share some common traits and similar
biochemical pathways and cellular functions, there are many notable differences that make each
creature stand out from the crowd. So even with the thread of sameness joining all the planets’
life forms, diversity and difference makes us take note of each creature’s uniqueness. Maybe
that’s why the cat is America’s favorite house pet ... cats are different!
This extraordinary four-legged feline has, for all of recorded time, evoked wonder and surprise,
superstition and affection, damnation, and deification. From pharaohs to philosophers to paupers,
the companionship of and affection for cats has been a result of the cat’s unique ability to make
us humans gaze in awe and admiration.
Eons of special environmental circumstances have forced the cat to evolve some interesting and
individualized biochemical activities. Let’s take a peek at how unique the cat is inside, in that
mysterious universe of liver and kidneys and glands and fluids where a million chemical reactions
are going about their biological business in silent obscurity. And to make our little peek at the
inner workings of the cat more interesting, let’s contrast a few of the cat’s biological activities to
those of our next most favorite companion the dog.
In so many obvious ways, cats look, act, react, and respond differently than dogs. You never see
a cat happily wag its tail; a dog’s reflexes are quick, a cat’s reflexes are incredible; dogs are
doers, cats are watchers. These differences are easily noted by simple observation. Now let’s
explore some of the unseen microscopic world of the cat -- the invisible world of metabolism and
chemistry that is just as real as those traits we can see with our eyes.
To begin with we must get a good grip on two terms ... carnivore and omnivore. The cat is
considered by scientists to be a strict carnivore and the dog is considered to be an omnivore.
Both species are in the Class Mammalia and the Order Carnivora, but here’s the difference: The
cat cannot sustain its life unless it consumes meat in some form. Dogs, however, are able to
survive on plant material alone; they do not have to consume meat. But always keep in mind that
dogs do best and by nature are primarily meat-eaters. Just because by definition they are
omnivores (can digest and utilize plant and animal food sources) does not mean that plant
material alone makes a good source of nutrition for the dog. Far too many dogs have been
undernourished by those cheap grain-based dog foods. And grain-based cat foods are even
So a good way to think of it is that cats are carnivores, dogs are omnivores, but they both have
evolved as hunters of other animals in keeping with their nature as meat-eaters.
There are numerous chemical substances that are required for a cat to remain alive. These
substances, some very complex chemical molecules and some very basic and simple, must be
provided along the internal chemical reaction pathways at all times. Like other living plants and
animals, the cat can manufacture most of its own required substances within its own body’s
chemical factory. For example, Vitamin C is a requirement for life sustaining processes for us
Mammalia, and dogs and cats make plenty of their own within their body’s chemical factory -- the
liver. We humans don’t make enough within our body chemical factory ... so to keep ourselves
alive we have to find some Vitamin C already made (preformed) somewhere in our environment,
gather or capture it, then eat it. Without the Vitamin C, we’d die.
Dogs and cats don’t have to worry about gathering, capturing, and eating other preformed
Vitamin C. They don’t care where their next grapefruit will come from because they make all the
Vitamin C they need inside their own personal chemical factory.
On the other hand, there are numerous nutrients and chemicals that cats need that they can only
acquire if they eat animal-derived tissues. That is, they need to prey on other living creatures that
do make the essential chemicals that cats don’t! Out of necessity, the cat has evolved ways to
hunt down, capture and eat this prey in order to "borrow" the prey's nutrients.
Outlined below are just a few of the unseen, but still very real biochemical differences between
cats and dogs. Look these over and you will be even more convinced that cats are different!
Vitamin A
Also called retinol, this vitamin is required at the cellular level by both cats and dogs.
Cats – Process little or no enzymes that will break down the plant-produced carotenoids. Must eat
preformed active Vitamin A (that is, Vitamin A that already has been converted from carotenoids
to its active form by some other creature such as a mouse or rabbit). Here’s a good example of
why cats are called strict carnivores ... they need to eat some other animal in order to "borrow" its
active Vitamin A!
Dogs – Have enzymes in the lining of the intestine that can break down plant carotenoids and
convert these into active Vitamin A.
An essential B vitamin (essential means must be eaten, can’t be made inside the body’s chemical
Cats – Can obtain Niacin only by eating the preformed vitamin. Cannot convert Tryptophan to
Dogs – Obtain Niacin in two ways. One is by converting a dietary amino acid call Tryptophan into
Niacin, and the other way is by eating preformed Niacin.
A building block for proteins, it is an amino acid. Arginine is vital to many of the animal’s internal
chemical factory’s functions. No Arginine and the entire factory goes on strike!
Cats – Are extremely sensitive to even a single meal deficient in Arginine and are unable to make
their own Arginine within their chemical factory. Cats need lots of protein, and Arginine is involved
in aiding the elimination of the protein waste products so the wastes don’t pollute the whole
Dogs - Are not very sensitive to low levels of Arginine in their diets and produce enzymes
internally that can aid production of Arginine.
An amino acid that is not built into proteins, but is distributed throughout most body tissues.
Taurine is important for healthy functioning of the heart, retina, bile fluid and certain aspects of
Cats – Must eat preformed Taurine. And since it is not found in plant tissues, cats must consume
meat to obtain Taurine. Therefore, Taurine is essential in the diets of cats. Here again, meat has
to be supplied to the factory so the Taurine can be extracted for its many uses.
Dogs – Make their own in their internal chemical factory.
It is a compound made from a sulfur amino acid (SAA) called Cysteine.
Cats – Have a much higher requirement for SAA than other Mammalia and are the only creatures
to manufacture the Felinine chemical. Felinine’s role in the overall function of the chemical factory
is unknown, but like most factories whose wastes generate offensive odors, any Felinine present
in the male cat’s urine alerts the neighbors that the factory is up and runnin’!
Dogs – Don’t know and don’t care what this stuff is.
Dietary Protein
Cats – If fed a perfectly balanced and 100-percent digestible protein in a diet, the cat will use 20
percent of that protein for growth metabolism and 12 percent for maintenance. Here’s any easy
way to say it ... cats need more protein in their diets than dogs do.
Dogs – If fed a perfectly balanced and 100-percent digestible protein in a diet, the dog will use 12
percent of that protein for growth metabolism and only 4 percent of that protein for maintenance.
Here's an easy way to say this ... dogs need less protein in their diets than cats.
Arachidonic Acid
An essential fatty acid that plays a vital role in fat utilization and energy production.
Cats – Cannot make their own Arachidonic Acid even in the presence of adequate linoleic acid.
The reason cats can’t make Arachidonic Acid from linoleic acid is because the cat’s chemical
factory (liver) contains no delta-6-desaturase enzyme to convert linoleic to Arachidonic. Tell your
cat owning friends about this one. Tell ‘em about the cat’s lack of liver delta-6-desaturase enzyme
and they’ll think you’ve got a Ph.D. in biochemistry!
Dogs – Can make their own Arachidonic Acid if they consume enough linoleic acid by eating
proper fats. Therefore, we can say that Arachidonic Acid is not an essential fatty acid for dogs.
Fasting and Starvation
Cats – Do not mobilize fat reserves for energy very efficiently and, in fact, break down non-fatty
body tissues for energy. This upsets the internal chemical factory and can lead to a very
dangerous feline disorder called hepatic lipidosis. Never put a fat cat on a starvation diet, it might
just put the entire factory out of business.
Dogs – Can tolerate prolonged fasts and utilize fat reserves for energy.
So, there you have an insight into some of the invisible goings-on in our friend the cat. It should
be obvious that a high quality, meat-based diet is imperative to a cat's wellness. There are no
vegetarian diets for cats! And feeding your cat a homemade concoction of meat may be a
disaster. Often, the best recourse is to find a good quality meat-based diet for your feline.
The next time you admire a cat's unique personality and behavior, and watch the way they
egocentrically carry themselves for anyone to see, remember ... hidden beneath that furry skin is
another unique and vast universe. There is a veritable chemical cosmos inside your cat that's just
as wondrous and magnificent as the cosmos above. You can't see it, but it's there, silently
following the rules of nature to sustain our unique and valued feline friends. And it's that complex
chemical cosmos, working it's fantastic magic, that prompts us cat lovers to say, truly ... cats are