The Predator Among Us
Most pet lovers are familiar with the idea that dogs and cats are carnivores. That is, both animals can and do derive valuable nutrition from the voluntary consumption of meat. In this regard, many mammals, including people, pigs, bears, raccoons, and myriad others have seemingly similar carnivorous tendencies. When meat is available, such animals will take advantage of the situation and eat it. There is a significant difference between cats and all of these other mammals, however. Dogs, people, pigs, bears, and raccoons, etc., are all omnivores that eat meat when it is available. Cats, big and small, are obligatory carnivores. The omnivore does not eat meat as a mandatory requirement for life; vegetable food sources can make up a very large part of their diet, and may even be properly balanced to provide all needed nutrients for health. For the cat, however, meat, and the nutrients found only in meat, are essential for survival.
The Cat Is Not a Small Dog
Critical differences between dogs and cats, the most popular of all household pet animals, are clearly illustrated in the genetic, anatomic, and metabolic differences between the two. Scientists who have studied the dietary habits of carnivores, omnivores, and herbivores tell us that these "rungs" on the food-chain were established and reinforced during the evolutionary histories of each type of animal (see www.catinfo.org/zorans_article.pdf). The work of these experts suggests that the members of the superfamily Feloidea, including today's cat, evolved rapidly in distant prehistoric times, but then stopped abruptly in that progression. Carnivorous animals belonging to other families of animals, including the Canoidea, to which the dog belongs, seem to have progressed beyond this point to meet changing evolutionary needs.
Good evidence for the cat's relatively ancient nature can be found in the lower number of chromosomes in its genetic makeup, compared with a much larger number for the group that includes modern dogs. The cat's cells carry thirty-eight chromosomes, while the dog's cells carry seventy-eight. This does not mean that the cat lacks physical and genetic sophistication equal to the dog. It means that it made a perfect and permanent fit within its spot in the environment early on and experienced little additional pressure to change its genes.
Dogs and cats also have remarkably different, but highly specialized, anatomy. Dogs have forty-two permanent teeth, whereas cats have only thirty. Dogs have more molars than do cats, with a specialized shape for crushing, associated with their intake of plant material. In contrast, the shape of feline teeth is specialized for grasping and tearing flesh. By its structure, the cat's jaw has far more restricted side-to-side and front-to-back mobility than does the dog's, limiting its ability to grind a varied vegetation-containing diet as the dog can do. The cat's eyes and ears are positioned forward on the head to provide exquisite acuity of vision and hearing when tracking prey, particularly at night. Retractable claws, seen on cats but not dogs, are another specialized feature of an animal that must chase, catch, and bring down all of its food in the form of wild prey.
The gastrointestinal tracts of the two species are also quite different. Those differences emphasize the differences in the natural diets of each. Science tells us that modifications in the basic structure of this important organ system from species to species are closely connected to diet. The cat's stomach, caecum (appendix), and colon, segments of the gastrointestinal tract most associated with digestion of vegetable matter, are smaller than those segments in the dog. The length of the feline intestine in proportionto its body length is short compared with that of the dog, indicating that the cat's evolutionary diet was highly digestible (protein and fat), whereas the dog consumes far more vegetable matter. The inner lining of the cat's stomach has significantly greater surface area than does the same part of the dog's stomach. Anatomists believe that increases in the relative size of this stomach area are an adaptation to the digestion of higher-meat, more calorie-dense diets. The caecum in the cat is very primitive, whereas it is much better developed in the dog. Once again, this portion of the gastrointestinal tract assists in the processing of fibrous, nonmeat dietary constituents.
Equally telling of the cat's strictly carnivorous origins are its nutrient requirements, especially its requirements for protein. Research done on the 1970s and '80s showed conclusively that protein requirements in kittens and cats far exceed those of puppies or dogs. The cat, unlike omnivores such as the dog, "burns" protein to make energy for its everyday use, under all circumstances. Most other animals burn large amounts of protein for energy only when protein is plentiful in the diet.
In contrast, the cat has an ongoing high requirement for protein to turn into energy, even when dietary protein intake is very limited. During starvation or excessive protein-restriction, the cat is forced to disassemble its body's own constituent proteins (enzymes, antibodies, organ tissues, and so on) to produce fuel for energy to keep the cells alive and functioning. Thus, in the most fundamental way, the health and tissue integrity of the cat is dependent upon the continual intake of highly digestible protein, especially protein from meat.
Another of the cat's claims to the top-predator spot in the food chain is the absolute requirement for an essential fatty acid, arachidonic acid, found only in meat. Also, cats must consume preformed vitamin A from animal-source foods because they are unable to make this essential vitamin from the beta carotene found in plants. The list of the specializations of the cat's internal machinery that reflect its evolutionary adaptations to a life as an obligatory carnivore goes on and on.
Not All Livers Are Alike
By far, the most fascinating characteristic of the cat compared to omnivores like the dog is the manner in which its liver functions. The cat's very high protein and amino acid requirements arise from the constantly high activity of certain enzymes in the feline liver. These enzymes disassemble the amino acids in protein to make them available for productionof energy in a process called gluconeogenesis. Essentially, the liver is the organ that is responsible for the high and constant burn rate of protein in the cat's body. Omnivores such as the dog have a liver that is also capable of this function, but omnivores turn the rate of this function up or down depending on how much dietary protein is available. In contrast, the cat's liver protein "burn rate" is set high at all times, even when dietary protein is scarce or entirely absent. Death from protein starvation can be very rapid in this species.
In the liver, protein amino acids are processed into glucose (sugar) and sent into the bloodstream to supply the body's need for this energy nutrient. In a meat-eating species like the cat, accustomed to little dietary carbohydrate in its evolutionary environment, the liver will manufacture the great majority of the animal's needed glucose, which is the primary energy supply for the animal's brain. Because there is little glucose in a high-meat diet, this is an essential task for an obligatory carnivore. The liver of omnivores, including people and dogs, have multiple enzyme systems for handling dietary carbohydrate; the cat has only one such enzyme system, with limited capacity to deal with high carbohydrate consumption.
Such specializations make the cat fit its niche perfectly; indeed, the fittest animal in a niche will be the one with the fewest and simplest systems to meet its survival needs. The cat's ancestors did not need the ability to turn their liver's protein burn rate up and down. Similarly, they did not require significant carbohydrate-handling capabilities. The specialized glucose-from-protein systems that have been genetically retained by the modern cat are always active at a high rate, obligating felines to eat more protein than their omnivorous counterparts. Because of this, unfortunately, the cat will suffer far more harm than will omnivores in situations where protein is insufficient or absent. We will see how important this requirement is when we discuss many of the common diseases of our pet cats.
Out of Africa
The present-day house cat (Felis domesticus) is generally thought to have descended thousands of years ago from a small wild cat (Felis lybica) native to the deserts of North Africa. Such a dry climate heritage would explain many distinct characteristics of this species. Cats are capable of surviving for long periods without water, and will naturally consume very little free water when they are feeding on canned cat food or fresh meat.Cats can produce urine that is highly concentrated compared to that of the dog and other animals that evolved in more water-rich environments. The cat's natural tendency to produce urine with a great deal of metabolic waste in a highly concentrated form can be dangerous if a cat feeds on a diet that is low in water, because this desert animal has a naturally low thirst drive. The cat that is consuming dry cat food seldom drinks enough additional free water to balance the dry state of the food. This results in especially concentrated urine with attendant medical problems, including certain kinds of bladder disease. Dry food also contains ingredients that interfere with the natural acidity of the cat's urine. Highly concentrated, alkaline urine from dry food consumption is associated with serious, even fatal urinary tract problems.
The Predator Lifestyle
The cat's ancient predator-behaviors are very much a part of its present-day life. Some wild cat species live solitary lives, associating closely with other adults of their species only during mating season. The most familiar of such solitary wild cats is the mountain lion, or cougar (Felis concolor). Other species, such as the African lion (Panthera leo), live relatively sedentary lives in small groups of animals, hunting and caring for the young in a collective manner, with a very defined geography that belongs to each group and which is protected by the group from outsiders that might take resources from that territory. Our pet cats are still very influenced by the primal behavioral instincts of their wild ancestors.
The domestic cat is like the lion in its social orientation. Despite the common belief that house cats are aloof and solitary, most naturally prefer to have companionship with a few members of their species. In such groups, which claim set territory with well understood boundaries, there is a clear pecking order, with the leader, or "alpha cat," often a female, living communally with its associates that have decreasing amounts of influence within the group. As long as the range of this group is large enough for the group size, there is general harmony, with only minor dominance "debates" between the alpha and associates.
From time to time, however, there may be individuals that do not fit with the group as a whole. For reasons that are not often clear, a young adult may become a pariah, or outcast. Such pariahs are individuals that cannot find friendship with the other cats in the community; rather, they will be chased and sometimes attacked by even other low-levelmembers of the group. In the wild setting, such cats would either leave the colony and seek other outcasts with which to start a new colony, or would live at the edge of the group, finding food and shelter as best they could without interacting with the others. Sometimes a youngster, often a male, will suddenly begin to demonstrate inappropriate and persistent dominance behaviors relative to others with high and low positions within the hierarchy. Dominant behaviors from a nonalpha cat are very disruptive of the welfare of the group and such a cat would also be driven from the colony, unless it can win the battles with older, more established members of the group and take their place in the hierarchy.
Feral cat colonies typically have clusters of same-sex cats that associate most closely. Females of reproductive age spend time together, and naturally their young kittens stay close to this female grouping until some time after they are weaned. Young adult males associate with one another in a sort of "bachelor band," but this group does not intermingle much with the females because one or a few older, more dominant males do the breeding that takes place within the colony. Dominant males live more solitary lives, except during the breeding season. Breeding males are highly competitive with one another, and each maintains a subterritory that is his own within the colony. Serious fights occur when a young male or another breeding male invades the well-marked subterritory of an established male. If there is insufficient space within the colony's total territory to allow for each assertive male to have breeding space, someone has to leave. Assertive males that cannot successfully challenge the dominant breeding male will be driven from the group and will seek to establish their own new groups.
Understanding these natural group relationships and interactions, and the possibilities for disruption of those dynamics, has great importance for understanding the behavior of pet cats, especially when they are kept in groups indoors.
Living with a Predator
The lesson in taking time to understand the cat's natural physiology and lifestyle is that altering that lifestyle will result in disease and behavioral disability. For all of their advanced intelligence, house cats cannot adjust to highly unnatural living circumstances any better than their much larger wild cousins on the African savannahs or the rain forests of Asia could. The domestic cat is not domestic. It is a small, essentially feral species that has made only modest accommodations to living intimately with humans.
I find the attraction some people feel for keeping wild species of felines as pets ironic. The seemingly less-exotic domestic cat is as wild in its mind, heart, and soul as the grand, fierce, big cats could ever be. Today, knowledgeable animal lovers understand that keeping a big cat requires great attention to such a cat's urgent needs for the right food, the right environment, and the right handling. We assume, however, that our house cats are so much different in their requirements for health and well-being. This is a mistaken belief.
True, our familiar house cat is not, generally speaking, a dangerous creature capable of killing or injuring us the way big cats are. Its size and deceptive amiability makes it a delightful and easy-to-keep pet. The differences between house cats and the lions, tigers, leopards, and innumerable other wild felines of movies and wildlife documentaries stop there, however. The predator that greets us at the door at the end of a busy workday, that shares our bed on a cold rainy night, and that slumbers in utter contentment on the top of our computer as we work in our office is an ancient, instinctive, hunting machine. I believe that the dreams of our beloved feline pets are filled with the thrill of the chase after prey, the comfort of napping in the incandescent equatorial sun, and the smell of monsoon rains beating relentlessly down on the towering shelter of jungle canopy. This is the smallest, gentlest cat's heritage and the core of its physical and psychological being.
If we would keep our cats healthy and happy throughout their naturally long lives, we cannot forget this truth.
YOUR CAT. Copyright © 2007 by Elizabeth M. Hodgkins. Foreword copyright © 2007 by Alice Villalobos. All rights reserved. For information, address St. Martin's Press, 175 Fifth Avenue, New York, N.Y. 10010.