The Carnivorous Cat
Cats are obligate (strict or true) carnivores, meaning they require certain nutrients that they cannot synthesize, which are only found in meat. The very name carnivore means devourer of flesh. Cats large and small, wild and domestic, need to eat meat as their main source of nutrients. Dogs, bears, and raccoons are all facultative (optional) carnivores or omnivores, meaning they can and do eat both meat and plant matter. However, given a choice, dogs will always choose meat if it is available.
A cat is solely designed to hunt, kill, eat, and process meat. Through millions of years of evolution, felids (felidae) have developed unique characteristics of anatomy, physiology, metabolism, and behaviour indicative of obligate carnivores.
Domestic cats have 38 chromosomes (strands of DNA in a cell's nucleus that carry genes) [ref] while dogs have 78 [ref]. This demonstrates that cats ceased evolving further after reaching their obligatory carnivorous status, genetically. They never evolved to incorporate plant materials into their diets.
Another difference between carnivorous carnivores (obligate) and omnivorous carnivores (facultative) is the type of teeth present. Cats have 30 teeth while dogs have 42. Dogs have more molars for grinding and chewing plant matter, while in cats, the upper third premolar and low molar are adapted as carnassial teeth, having no flat crowns for grinding. Meat is digested in the stomach, so there is no need to chew it.
Tongue, Jaws & Musculature
The felid tongue is covered with horny papillae, which help to rasp meat from the bones of their prey.
For the most part, the jaws of the cat only move vertically. This prevents them from being able to chew, but makes it easier for their powerful jaw muscles to hold struggling prey. Cats' heads are highly domed with a short muzzle. The skull has wide zygomatic arches (cheekbones) and a large sagittal crest (ridge of bone running lengthwise along the centre of the top of the skull), both of which allow for the attachment of strong jaw muscles.
Cats, unlike omnivores, do not have the enzyme, amylase, in their saliva which begins the breakdown of carbs in the mouth. This is required since the metabolism of carbs takes a long time. Cats utilise the enzyme hexokinase [ref] for the metabolism of low-glucose loads in their diet. They lack the ability to metabolize high-glucose loads.
Cats only possess hepatic (liver) enzymes to metabolize a high-protein diet and in lieu of this type of continuous high-meat-protein diet, will start to breakdown their own muscles and organs to achieve this.
Dogs and cats do however produce an enzyme in the mouth called lysozyme, that kills bacteria and other harmful pathogens upon contact, a useful trait for a meat eater.
Cats have a special need for the amino sulfonic acid, taurine, essential for the formation of bile salts which aid in the digestion of fats and absorption of fat soluble vitamins, healthy eyes, and heart function. Taurine is therefore essential for cardiovascular function, and development and function of skeletal muscle, the retina, and the central nervous system. Taurine occurs naturally in fish and meat. Cats are unable to manufacture taurine themselves because they do not have enough of the enzymes to synthesize it from the amino acids methionine and cysteine, therefore, it must be in their diet.
Vision & Hearing
Cats' eyes face forward, allowing for binocular vision for hunting and they have excellent night vision allowing them to hunt their prey, predominantly small rodents, in very low light. Cats also have excellent depth perception, which allows them to move accurately and consistently based on the location of their prey and it is also the reason they are adept at climbing and jumping.
Cats hear high pitched sounds such as those emanating from small rodents. "The hearing range of the cat extends from 48Hz to 85kHz, giving it one of the broadest hearing ranges among mammals." [ref] "Analysis suggests that cats evolved extended high-frequency hearing without sacrifice of low-frequency hearing." [ref] For comparison, the human range is approximately 20Hz to 20kHz.
Vibrissae (Whiskers) & Claws
A cat's whiskers aid in hunting by moving forward to feel for prey within reach when either the prey is too close or can't be seen by the cat, in bright or low light. The whiskers also pick up vibrations alerting it to prey activity.
Cats have retractable claws for chasing after, grasping, and holding prey.
Cats cannot synthesize vitamin D from sunlight due to insufficient 7-dehydrocholesterol in their skin, and therefore must receive their vitamin D through dietary means, in this case, animal products. Meat, eggs, and fish oil are excellent sources while the only vegan source is mushrooms.
Vitamin A occurs naturally, only in animal tissues. While omnivores and herbivores can convert beta-carotene (an inactive form from plants) to vitamin A, cats cannot convert beta-carotene into the usable vitamin A they need, and therefore need the preformed version from their diet.
"The cat's intestine is shorter in proportion to its body size." [ref], suggesting that the cat's diet has extremely digestible meat protein and fat for a fast transit time as opposed to fibrous plant material for a prolonged digestive time.
Intestinal length, as determined by the ratio of intestine to body length, is shorter in cats than omnivores and herbivores. The ratio for cats is 4:1, meaning that the intestines are four times longer than the length of the cat. By contrast, this ratio is 14:1 for pigs, in other words, the intestines are fourteen times longer than the length of the pig, allowing for digestion of high carb loads.
The larger stomach surface area and non-functioning caecum (beginning of the large intestine) in the cat, also indicate a diet of high-meat-protein with higher caloric value by limiting the cat's capability to use poorly digestible starches and fibre by bacterial fermentation in the colon. The small and simple stomach of the cat also indicates a highly digestible, multiple meal behaviour [ref].
A cat's sense of taste differs from other mammals in one important way - cats have a genetic mutation that makes the sweet receptors on their tongues non-functional. When cats in a study were presented with sugar-laced water and plain water, they showed no preference for either. This mutation likely helped cats evolve towards all-meat diets [ref].
In mammals, the sense of taste helps in the evaluation and consumption of nutrients, and in avoiding toxic substances and indigestible materials. Not all mammals can taste flavours, and the number of taste buds found on the tongue will determine the intensity of the flavour. Cats can taste salty, bitter and sour flavours, dogs are able to taste sweet, salty, bitter and sour flavours.
Cats have 470 taste buds, dogs 1700, and humans, for comparison, 9000.
Water Chiefly Supplied by Food
Dry food is missing the most important nutrient, water. Many cats can and will live a long life on a dry or dry/canned diet, however, we don't know which cats are genetically able to do so until it's too late, typically being diagnosed with chronic renal (kidney) disease (CKD). By the time most cats present with CKD, they have lost more than 70% of kidney function. This is a terminal condition.
Cats have a low thirst drive due to their desert adaptation and do not ingest enough free water to compensate for the lack of water in their diet, and are therefore, chronically dehydrated.
Fatty Acid Requirements
Why Raw Fooding for Cats?
Cats, through desert adaptation, require water as a component of their food. They also lack the metabolic pathways to efficiently process plant materials, thus defining them as obligate carnivores; their food should consist only of meat, fat, bones, and organs. These are two very simple yet fundamental facts of feline nutrition.
Many feline diseases, such as diabetes, obesity, urinary tract disorders, chronic renal disease, and irritable bowel syndrome can be directly attributed to low moisture, low-meat-protein, and high-carbohydrate levels that plague many of today's commercial produced cat foods.
However, many cats do survive on these dry, supplemented, plant-based diets, but they do not thrive.
Reference and Articles
- "Feline Nutrition: Nutrition for the Optimum Health and Longevity of your Cat" by Lynn Curtis (Amazon);