Science Corner

DOGS ARE FROM VENUS; CATS ARE FROM MARS
By Cecile Ashen-Young

Both the cat and the dog are mammalian companion animals, and both species belong to the order Carnivora. There are, however, distinct differences in their physiology, their behaviour, and their nutritional requirements. The dog belongs to the Canoidea superfamily and its evolutionary history indicates a diet that is more omnivorous in nature than carnivorous. The cat, on the other hand, belongs to the Feloidea superfamily and its evolutionary development has been characterised by a purely carnivorous diet (Case, 2011). 

Dogs and cats are often grouped together in terms of feeding and nutritional requirements, but the cat exhibits specific nutritional idiosyncrasies that are of practical significance in that they require more stringent dietary requirements than the dog. The protein needs of the cat are, in some parts of the life cycle, almost twice that of the dog. Cats need more protein in the diet to maintain their normal rates of metabolism: to supply the energy to convert amino acids to glucose, and for the synthesis and excretion of urea.  Their rapid rates of metabolism and their dependence on certain nutrients found only in animal tissue, such as taurine, arachidonic acid, and preformed vitamin A, means that companion cats require the addition of animal tissues in their diet to meet their peculiar nutritional needs (McNamara, 2006). Taurine is involved in retinal function and bile salt formation. Cats are totally dependent on taurine for the formation of bile salts and, unlike dogs, cannot make enough to meet their needs. Arachidonic acid is a complex essential fatty acid found mostly in animal tissue. Cats need a certain quantity of arachidonic acid, particularly during the reproduction stage of the life cycle, but have a limited capacity to synthesize it. Similarly, cats are unable to synthesize vitamin A from beta-carotene, and must be provided with dietary, preformed vitamin A, which is found in animal fats (Module 6.1 Special Requirements of Cats, 2005).

Despite the differences in the nutrient requirements of dogs and cats, the primary goals of feeding both are the same: promote healthy eating behaviors, promote a normal growth rate, support gestation and lactation and, above all, maintain optimal health (Case, 2011).

Similar to dogs, cats can withstand a significant loss of proteins and fats but are much less tolerant of body water losses. The two main sources of daily water intake of cats are the water present in their food and the water they drink voluntarily. A cat that is fed a canned diet, which contains up to 78% water, can maintain normal water balance and will have very low voluntary water intake. On the other hand, a cat fed on a dry diet will have to compensate by getting almost all of his daily water intake though voluntary drinking, and so requires frequent access to clean drinking water. Unlike dogs, cats are relatively insensitive to body water loses and may be less efficient than dogs at compensating for dietary and environmental changes by increasing voluntary water intake.  This can contribute to problems with maintaining adequate hydration which can increase the risk of the cat developing problems relating to the urinary and other body systems (Case, 2003).          

Unlike dogs, cats are obligate carnivores. An obligate or true carnivore is an animal that requires meat in its diet and can, in fact, thrive without any carbohydrates. Instead of carbohydrates, they use protein as their primary energy source. True carnivores lack the metabolism required to properly digest vegetable matter. They have adapted to a protein-rich, fat-rich, carbohydrate-poor diet. 

Cats are the only major companion animals that are true nutritional carnivores. They eat meat and are therefore considered carnivores; they must eat meat to survive and are therefore obligate carnivores. Cats are very efficient hunters, ingesting not only the flesh and organs of their prey, but also the partially or wholly digested plant matter eaten by the prey from which they are able to derive some nutrients.   

While the dietary requirements of cats, as obligate carnivores, may be sufficient for maintenance, the companion cat must be provided with a mixture of ingredients that supply the necessary nutrients as well as an adequate supply of animal-derived raw materials in order to maintain a properly balanced complete diet.

References

Case, L. P. (2011). Canine and Feline Nutrition.Missouri: Mosby, Inc.

Case, L. P. (2003). The Cat: Its Behavior, Nutrition & Health. Iowa Blackwell Publishing Company

McNamara, J. P. (2006). Principles of Companion Animal Nutrition.New Jersey: Pearson Education, Inc.

Module 6.1 Special Requirements of Cats.(2005). Retrieved April 26, 2011, from Advance, Advanced Pet Nutrition. 

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