This amazing planet that supports life is home to an amazing variety of complex organisms. While all organisms share common characteristics, similar biochemical pathways, and cellular functions, there are also many notable differences that set each organism apart from the others. So while commonalities connect all life forms on Earth, the diversity and differences allow us to focus on the uniqueness of each organism. Perhaps that’s why cats are America’s favorite pet… they’re different!
Throughout all recorded times, these extraordinary four-legged felines have inspired wonder and amazement, superstition and affection, damnation and deification. From pharaohs to philosophers to paupers, our feline friendships and affections are a result of cats’ unique ability to make us humans look upon them with awe and admiration.
Over hundreds of millions of years, cats have evolved a fascinating and unique biochemical activity governed by special environmental conditions. In the mysterious world of the liver, kidneys, glands and body fluids, where millions of chemical reactions continue their biological activity silently and unnoticed, we take a peek inside just how unique a cat’s body is. To make things even more fascinating after this brief glimpse into the inner workings of cats, let’s compare some of their biological activity with that of our next beloved companion, the dog.
Cats are clearly different from dogs in appearance, behavior, reactions and responses. We have never seen a cat wag its tail with joy. Dogs have quick reflexes and cats have phenomenal reflexes. Dogs are action people, cats are observation people. These differences are easily seen with simple observation. So let us explore the invisible microscopic world of cats, the invisible world of metabolism and chemistry that is as real as the properties we can see with our eyes.
First, you need to have a firm understanding of the two terms carnivore and omnivore. Scientists consider cats to be strict carnivores and dogs to be omnivores. Both species belong to the order Carnivora of the mammalian class, but here is the difference: Cats cannot survive without eating meat in some form. Dogs, on the other hand, can survive on plant matter alone and do not need to eat meat. However, always keep in mind that dogs live best and are primarily carnivores by nature. Just because dogs are omnivores by definition (able to digest and utilize plant and animal food sources), does not mean that plant matter is the only good source of nutrition for them. Too many dogs are undernourished by cheap grain-based dog food. And grain-based cat food is even worse.
So it’s best to think of cats as carnivores and dogs as omnivores, but both evolved to hunt other animals in keeping with their carnivorous nature.
Cats need many chemicals to survive. These substances, some very complex chemical molecules, some very basic and simple, must be constantly supplied along the chemical pathways in their bodies. Like other living plants and animals, cats can make most of the substances they need in their own chemical factories. For example, vitamin C is necessary for our mammalian life processes, and dogs and cats make it in abundance in their own chemical factories, the liver. We humans cannot make it in sufficient quantities in our own chemical factories. Therefore, to survive, we must find vitamin C that has already been made (pre-produced) somewhere in the environment and collect or catch it to eat. Without vitamin C, we would die.
Dogs and cats don’t have to worry about collecting, catching, or eating other pre-made Vitamin C. They don’t have to worry about where their next grapefruit is going to come from because they’re making all the Vitamin C they need right within their own chemical factory.
However, many of the nutrients and chemicals cats need can only be obtained by eating animal tissue, which means they must prey on other organisms that produce the essential chemicals that cats don’t make. Out of necessity, cats have evolved ways to hunt, capture, and eat their prey in order to “borrow” the nutrients from their prey.
Here are some of the invisible, yet very real, biochemical differences between cats and dogs that should further convince you that cats are different from dogs:
Vitamin A
Also known as retinol, this vitamin is needed at a cellular level in both cats and dogs.
Cats – have little to no enzymes that break down plant produced carotenoids. They need to consume already formed active Vitamin A (i.e. Vitamin A that has been converted from a carotenoid into its active form by other organisms such as mice or rabbits). This is a great example of why cats are called strict carnivores… they need to eat other animals to “borrow” active Vitamin A.
Dogs – They have an enzyme in their intestinal lining that can break down plant carotenoids and convert them into active Vitamin A.
Niacin
An essential B vitamin (essential means that it cannot be produced in the body’s chemical factories and must be ingested).
Cats – Niacin can only be obtained by eating preformed vitamins. Tryptophan cannot be converted to niacin.
Dogs – There are two ways to get niacin: by converting a dietary amino acid called tryptophan into niacin, or by eating pre-made niacin.
Arginine
An amino acid that is the building block of proteins, arginine is essential for the functioning of many of the chemical factories in animals’ bodies. Without arginine, the entire factory would go on strike.
Cats – are extremely sensitive to even an arginine deficient diet and cannot make their own arginine in the chemical plant. Cats require large amounts of protein and arginine helps to eliminate protein waste so that waste does not contaminate the entire plant.
Dogs – They are not very sensitive to low levels of arginine in their diet and produce an enzyme in their bodies that helps make arginine.
Taurine
An amino acid that is not incorporated into proteins but is distributed throughout most body tissues, taurine is important for the healthy function of the heart, retina, bile, and certain aspects of reproduction.
Cats – They must eat pre-made taurine. Also, cats must eat meat to get taurine as plant tissue does not contain it. Therefore, taurine is essential in a cat’s diet. Again, meat must be fed to factories to extract taurine so that it can be used for various purposes.
Dogs – They make their own chemicals in their internal chemical factories.
Felidae
It is a compound made from a sulfur amino acid (SAA) called cysteine.
Cats – They have a higher requirement for SAA than any other mammal and are the only animal that manufactures feline chemicals. The role of felines in the overall functioning of a feline chemical plant is unclear, but like most plants whose waste produces a foul odor, the presence of feline chemicals in the urine of male cats alerts nearby residents that a plant is operating.
Dog – I don’t know what this is, and I don’t care.
Dietary Protein
Cats – When fed a fully balanced, 100% digestible protein diet, cats will use 20% of that protein for growth metabolism and 12% for maintenance. Simply put, cats require more protein in their diet than dogs.
Dogs – When fed a fully balanced, 100% digestible protein diet, dogs will use 12% of that protein for growth metabolism and only 4% of that protein for maintenance. Simply put, dogs require less protein in their diet than cats.
Arachidonic acid
An essential fatty acid that plays an important role in fat utilization and energy production.
Cats – Even if they have enough linoleic acid, they cannot make arachidonic acid themselves. The reason cats cannot make arachidonic acid from linoleic acid is because their chemical factory (their liver) does not have the delta-6-desaturase enzyme to convert linoleic acid to arachidonic acid. Tell this to your cat-owning friends; they will think you have a PhD in biochemistry when you tell them that cats’ livers do not have the delta-6-desaturase enzyme.
Dogs can make their own arachidonic acid if they consume enough linoleic acid from an adequate fat diet, so arachidonic acid is not considered an essential fatty acid for dogs.
Fasting and Starvation
Cats – They cannot efficiently mobilize their fat stores for energy and will actually break down non-fatty tissue for energy. This causes the body’s chemical factories to go haywire and can lead to a very dangerous feline disease called hepatic steatosis. Never put an overweight cat on a starvation diet as the entire factory can shut down.
Dogs – They can withstand long periods of fasting and can use their fat stores for energy.
Now you know some of the invisible activities of our cat friends. It is clear that a high-quality meat-based diet is essential for cat health. There is no vegetarian diet for cats, and feeding your cat homemade meat dishes can be disastrous. In many cases, your best bet is to find a high-quality meat-based diet for your cat.
The next time you admire your cat’s unique personality and behavior, or see their selfish behavior that is so obvious to everyone, remember that beneath that furry skin lies another unique and vast universe. Inside your cat is a veritable chemical universe, as wonderful and magnificent as ours. It is invisible, but it is there, silently obeying the laws of nature to provide for our unique and precious feline friends. And it is this complex chemical universe working its wonderful magic that compels us cat lovers to say, “Cats are really different!”
image: Marianne Perdomo /Flickr
