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 planet's life forms, diversity and difference makes us take note of each creature’s uniqueness. Maybe that’s why the cat is America’s favorite housepet ... 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 worse!
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!
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 factory.)
Cats – Can obtain Niacin only by eating the preformed vitamin. Cannot convert Tryptophan to niacin.
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 factory!
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 reproduction.
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.
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.
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 different!
Image: Marianne Perdomo / via Flickr
Help us make PetMD better
Was this article helpful?