Cats: obligate carnivore (Proceedings)
In their natural environment, cats are an obligate carnivore, meaning that their nutritional needs are met by eating a diet that consists of animal-based proteins (i.e. mice, birds). How have our efforts to domesticate cats been affected by this dietary requirement?
Strictly speaking, cats and dogs are members of the order Carnivora and are therefore, classified as carnivores. From a dietary perspective, dogs are omnivores and cats and other members of the suborder Feloidea are strict carnivores. Domesticated cats (Felis catus) have evolved unique anatomic, physiologic, metabolic and behavioral adaptations consistent with eating a strictly carnivorous diet.
Feeding BehaviorsThe evolutionary history of the cat indicates that it has eaten a purely carnivorous diet throughout its entire development. Feeding behaviors that have evolved to fit this lifestyle include searching, hunting and caching of prey as well as postprandial behaviors such as grooming and sleeping. Feral or outdoor cats feeding primarily on mice, voles and insects tend to live solitary lives when food is scarce and spread over a large area, but when food is plentiful and concentrated as with households, dumps and farms cats can be found living in large groups. Cats typically eat 10-20 small meals throughout the day and night. This eating pattern probably reflects the relationship between cats and their prey. Small rodents make up ~40% or more of the feral domestic cats diets, with small rabbits, insect, frogs and birds making up the remainder. The average mouse provides ~30 kilocalories or an estimated 8% of feral cat's daily energy requirements. Repeated cycles of hunting throughout the day and night are required to provide sufficient food for the average cat. House cats typically continue this pattern by eating 10-20 small meal throughout the day and night with each meal having a caloric content of ~23 kilocalories, very close to the caloric value of one small mouse.
For thousands of years the primary economic value of cats has been their hunting skills. Until recently, there has been little or no selective breeding done to alter their behavior or looks. The predatory drive is so strong in cats that they will stop eating to make a kill. This behavior allows for multiple kills, which optimizes food availability. Supplemental feeding may reduce the time spent hunting, but otherwise will not alter hunting behavior.
Cats are very sensitive to the physical form, odor and taste of foods. They consume live prey beginning at the head, this head first consumption is dictated by the direction of hair growth on the prey. Food temperature also influences acceptance by cats. They do not readily accept food served at either temperature extreme, but prefer food near body temperature (~ 38°C, 101.5°F) as would be found with freshly killed prey. House cats accustomed to a specific texture or type of food may refuse foods with different textures. An individual cat's preferences are often influenced by early experiences (good or bad). Many cats will choose a new food over a diet that is currently being fed. The reverse is true in new or stressful situations, such as illness or hospitalization, where cats tend to refuse novel foods. This can be important when trying to switch foods or forms of food fed.
Cats have adapted physiologically to the life of a hunter. Their visual acuity is greater than that of dogs. In addition, their sense of hearing is well developed- their ears are upright, face forward and have 20 associated muscles to help them precisely locate sound. Their highly sensitive facial whiskers and widely dispersed tactile hairs are thought to help them hunt in dim light and to protect their eyes. Sharp and dagger-like, their retractable claws are ideal for capturing and securing prey, yet they are easily retracted to decrease noise when stalking.
The scissor-like carnassial teeth are ideal for delivering the cervical bite used to severe the spinal cord and immobilize or kill prey.
Their stomachs are smaller than dogs and simpler in structure. Because cats do not consume large meals, the stomach is less important as a storage reservoir.
Intestinal length, as determined by the ratio of intestine to body length is markedly shorter in cats than in omnivores and herbivores. The ratio for cats is 4:1, meaning that the intestinal length is 4 times longer than the length of the cat, for dogs this is 6:1 and for pigs 14:1. Cats do have greater villus height in their intestinal lining improving their absorptive capacity over that of dogs, so that overall they are only ~10% less efficient in digestion especially with complex starches or fibers even with their shorter intestinal length.