CARNIVORE NUTRITION: Basics
Mark S. Edwards, Ph.D.
The specialization of many species to a strictly carnivorous diet has lead to several distinct metabolic differences, in comparison with other non-carnivorous species (MacDonald et al., 1984). As a result of these metabolic characteristics, "true" carnivores, including insectivores and piscivores, may require dietary sources of several nutrients which are unique among domestic animals. These specialized nutrient requirements are discussed below.
Domestic cats as "The model"
The literature on digestive capabilities, energy and nutrient metabolism of captive exotic felids is biased toward the larger cats (e.g., Panthera spp.) (Morris et al., 1974; Mills, 1980; Barbiers et al., 1982; Allen et al., 1994). Perhaps the bias is simply due to the number of individuals housed in captivity which could be recruited into these studies. Another explanation may be the reliability of applying maintenance energy requirements of the domestic cat (Felis silvestris catus) to larger species (Allen et al., 1994). Regardless, the majority of the information which is used to formulated captive feeding programs for strict carnivores is based on domestic cats. Supplemental information may be obtained from literature on natural feeding habits, nutrient composition of foods consumed by free-ranging animals, and gastrointestinal tract anatomy.
Cats have a relatively higher nitrogen (crude protein) requirement than most domestic mammals (Rogers and Morris, 1982). It is thought that cats have a reduced ability to regulate key enzymes involved in protein metabolism in response to changes in dietary protein intake. This results in an elevated loss of nitrogen, which is accommodated by the higher dietary protein intake.
Amino acids required by cats are supplied by dietary protein. Cats, like other monogastric species, require 10 alpha-amino acids. In addition to these 10 dietary essential amino acids, cats have a dietary requirement for taurine, a sulphur amino acid. The cat's requirement for dietary taurine appears to be a result of both the need for taurine conjugates contained in bile salts and the low efficiency in the hepatic synthesis of taurine from methionine and cystine (NRC, 1986). A taurine deficiency will result in feline central retinal degeneration (FCRD), which includes reduced visual acuity and, in advanced stages, extensive destruction of the visual elements. The current dietary requirement for maintenance and reproduction is 400 and 500 mg/kg diet, respectively.
Although most mammals can convert dietary sources of linoleic acid (18:2n6) to the other essential fatty acids, felids are unable to make the conversion of dietary linoleic acid to arachidonic acid (20:4n6). Consequently, cats require a dietary source of arachidonic acid. The current minimum recommended dietary concentrations of linoleate and arachidonate are 5 and 0.2 g/kg diet, respectively (NRC, 1986).
Cats lack the ability to utilize dietary or intravenous sources of ß-carotene, a compound with pre-vitamin A activity. Therefore, cats require preformed vitamin A in their diet (NRC, 1986).
Many animals are able to meet their requirement for niacin from hepatic synthesis of the vitamin from tryptophan. Even though cats have the hepatic enzymes to carry out this synthesis, the removal of an intermediate metabolic is so great that virtually no niacin is produced. Diets for felids are supplemented with a minimum of 40 mg niacin/kg diet (NRC, 1986).
Another syndrome seen in felids in which dietary nutrient composition plays a major role is feline urological syndrome (FUS). FUS is characterized by the high incidence of struvite urolithiasis. Although the etiology of this syndrome still unclear, it is obviously multifactorial. Factors which contribute to the formation of the struvite urolithes include improper urine pH and dietary components which affect urinary pH, magnesium content of the diet, and water intake. Further discussion of FUS is beyond the scope of this presentation.
Food items often used
The gastrointestinal tract of felids is relatively short (NRC, 1986). This results in rapid rate of digesta passage, and therefore a somewhat lower digestibility for many natural feedstuffs than the rat and dog (Kendall et al., 1983). Thus, high quality feeds best serve this species (NRC, 1986).
The types of foods offered to captive small felids is typically dependent upon the size of the felid and total animal collection, as well as support facilities and staff. Historically, zoos fed skeletal muscle, typically horse or beef, or meat-mixtures prepared on-site. Due to the nutrient imbalances of skeletal muscle, a diet which consists exclusively of this food item should never be used (Ullrey and Bernard, 1989).
The availability of commercially prepared and nutritionally complete foods for felids has nearly eliminated the incidence of nutritional pathologies associated with feeding unsupplemented muscle meats (Allen et al., 1994). These nutritionally complete foods are produced in a chopped and frozen horsemeat "loaf" form, as well as canned diets. Recently, interest has been growing in the use of dry, extruded particles or kibble. This form has been widely used in the pet food industry,
The term "prey items" is often used synonymously for whole animal bodies, either living or killed. Mammalian, avian, fish and invertebrates are commonly fed, with reptilian prey used occasionally.
Provisioning captive carnivores with food or related items which provide oral stimulation is essential (Lindburg, 1988). The presentation of bones to captive tigers twice weekly was effective in reducing the formation of plaque and dental calculi in animals fed an otherwise "soft" diet (Haberstroh et al., 1984).
Allen, M.E., O.T. Oftedal, K.E. Earle, J. Seidensticker, and L. Vilarin. 1995. Do maintenance energy requirements of felids reflect their feeding strategies? Proceedings of the First Annual Conference of the Nutrition Advisory Group. Toronto, Ontario, Canada.
Barbiers, R.B., K.M. Vosburgh, P.K. Ku, and D.E. Ullrey. 1982. Digestive efficiencies and maintenance energy requirements of captive wild felidae: cougar (Felis concolor); leopard (Panthera pardus); lion (Panthera leo); and tiger (Panthera tigris). Journal of Zoo Animal Medicine 13:32-37.
Haberstroh, L. I., D. E. Ullrey, J. G. Sikarskie, N. A. Richter, B. H. Colmery and T. D. Myers. 1984. Diet and oral health in captive Amur tigers (Panthera tigris altaica). Journal of Zoo Animal Medicine 15: 142-146.
Lindburg, D. G. 1988. Improving the feeding of captive felines through application of field data. Zoo Biology 7: 211-218.
MacDonald, M.L., Q.R. Rogers, and J.G. Morris. 1984. Nutrition of the domestic cat, a mammalian carnivore. In: Annual Review of Nutrition (vol. 4) (W. Darby, H. Broquist, R. Olson, eds.). Pp. 521-562. Annual Reviews, Inc. Palo Alto, CA.
Mills, A.W. 1980. A comparative study of the digestibility and economy of three feline diets when fed to lions and tigers in confinement. In: The Comparative Pathology of Zoo Animals (R. Montali and G. Migaki, eds.). Pp. 87-91. Smithsonian Institution Press. Washington, D.C.
Morris, J.G., J. Fujimoto, and S.C. Berry. 1974. The comparative digestibility of a zoo diet fed to 13 species of felid and a badger. International Zoo Yearbook 14:169-171.
National Research Council. 1986. Nutrient Requirements of Cats. Nutrient Requirements of Domestic Animals. National Academy Press, Washington, D.C.
Rogers, Q.R., and J.G. Morris. 1982. Do cats really need more protein? Journal of Small Animal Practice 23:517-613.
Ullrey, D. E. and J. B. Bernard. 1989. Meat diets for performing exotic cats. Journal of Zoo and Wildlife Medicine 20(1): 20-25.
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