Feline Nutrition

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It is an erroneous and simplistic statement to declare that cats live longer in the 21st century than cats in previous centuries solely because of improved nutrition. In parallel to Western-society's slow loss of life quality in association with adopting a 'fast-food' mentality, the argument that cats are showing an equal decline in life quality can be supported by the rising incidence of poor health prognosticators; diabetes mellitus, hyperthyroidism, irritable bowel disease, food allergy dermatitis and obesity[1].

It appears self-evident that what has been most contributory to feline longevity is behavioural changes of the care-givers by firstly adopting an indoor lifestyle for their pet and secondly, desexing, which together have significantly reduced death by overpopulation, territorial conflicts, infectious diseases such as FIV and various other misadventures such as motor vehicles accidents, gun shot wounds, etc. Feline longevity has also been augmented through the use of core vaccines, the eradication of parasites, and the eugenics of eliminating genetic defects[2]. Nutritional changes rank last on this list of radical improvements in feline longevity.

In an undomesticated environment, a wild cat will hunt small animals to survive. If we consider that the average human needs 1g protein/kg bodyweight/day, by comparison, a cat needs to eat approximately 10g protein/kg bodyweight/day. Nutritional analysis of a cat's wild diet has shown that it contains approximately 90% protein, 5% fat and 5% carbohydrates, mainly from insects, rodents and small birds (August, 2006). This can be compared to a typical commercial dry cat food which contains 30% protein, 20% fat and 30% carbohydrates (remaining 20% minerals and water)[3].

By the nature of their cooking method, commercial dry cat food preparations are unable to provide higher protein diets as a 'dry food' preparation without 'spoiling' and bacterial contamination occurring. The low protein and high carbohydrate content of commercial dry food underpins their predisposition to inducing obesity in indoor-confined sedentary cats. Tinned cat food (using the 'canning' method which effectively sterilizes the contents) fair somewhat better in approaching 'wild food' by allowing a high-protein meal with a long-shelf life and thus more closely matches 'wild food' protein and carbohydrate percentages, however, there is a linear relationship between quantity of tinned food consumed by cats and the incidence of hyperthyroidism[4]. Commercial cat food-related toxicity is also another concern for cat owners.

Unlike an omnivore (e.g human, dog), whose digestive system consists of a fairly large small intestine and relatively large stomach, the carnivore's system consists of a fairly short small intestine and relatively small stomach. Thus, a carnivore's optimum diet must be concentrated, highly digestible, and low in residue because its body is designed to digest primarily protein. If an excess of carbohydrates is included in the diet, much of what the carnivore eats is only partially digested by the time it reaches the large intestine for fecal formation, overloading the digestive and excretory systems[5]. This is reflected in recent studies of the African wildcats, where feeding commercial kibble instead of fresh meat resulted in the cats needing to consume more kibble to meet their protein requirements, resulting in early stage liver disease (elevated liver enzymes)[6].

Although what a cat eats is determined biologically by hunger and the taste and smell of the food, what a domesticated cat actually consumes is determined by what it is presented with. In domestication, a cat's diet is dictated by its care-giver's bond with the cat, his/her finances, his proclivity for a fresh versus commercial food, the marketing-influenced predilections for the type of food purchased and the care-giver and cat's daily moods. Surfeit to this diet are the cat's ability to scavenge during its brief outdoor activities (neighbor's cat's bowl, hunting, etc) and what it can coerce a care-giver to give it.

Feline evolution and how it affects dietary requirements

Cats, being obligate carnivores, rely on nutrients in animal tissues and have, due to evolutionary pressure, developed a number of peculiarities in protein and fat metabolism.

Adult cats require more dietary protein than omnivorous species, maintain a consistently high rate of protein oxidation and gluconeogenesis and are unable to adapt to reduced protein intake. Furthermore, cats have a higher requirement for essential amino acids and essential fatty acids. Coupled with an inability to conserve certain amino acids, including methionine, cysteine, taurine and arginine, this necessitates a higher dietary intake for cats compared to most other species[7].

For example, the lack of cat’s ability to synthesize sufficient vitamin A from carotene, ornithine from glutamic acid, arachidonate from linoleate, and taurine from cysteine results from a complete deletion or severe limitation of the enzyme or pathway that makes each nutrient. Other nutrient requirements, such as the absolute requirement for niacin and the high protein requirement, appear to result from the high activity of one or more enzymes and the fact that these enzymes are not adaptive in the cat.

As well, cats cannot decrease picolinic carboxylase in order to force tryptophan toward the niacin-synthetic pathway nor can it decrease the urea cycle enzymes when dietary protein is decreased in the diet in order to conserve nitrogen. Indeed, the cat appears to have less capability to adapt to most changes in dietary composition because it cannot change the quantities of enzymes involved in the metabolic pathways. This evolutionary development has resulted in more stringent nutritional requirements for cats than for omnivores such as the rat, dog, and man. What little evidence exists for other carnivore species leads us to suggest that this pattern may well be common among other strict carnivores. The metabolic differences between the cat and omnivores provides the researcher with a useful animal model for studying the biochemical basis of some nutrient requirements. For example, because there is no significant conversion of linoleate to arachidonate in cat liver, the physiological functions of linoleate can be determined independent of it having a role as a precursor of arachidonate[8].

Cats also require greater daily intake of several B-vitamins compared to other species and are predisposed to depletion during prolonged inappetance.

Daily nutritional requirements

Daily protein requirements 10 g/kg bodyweight
Daily fat requirements 2 g/kg bodyweight
Daily carbohydrate requirement 1 g/kg bodyweight
Daily energy requirements 45 kcal/kg bodyweight (adult)
100 kcal/kg bodyweight (kitten/pregnant/lactating)
Daily water requirements 10 mL/kg bodyweight
Daily fibre requirements 1 g/kg bodyweight

Resting energy requirement (RER) can be calculated as follows:

RER (kcal/day) = 70 + (30 x bodyweight (kg))


Daily vitamin requirements

Nutrients Min requirement Recommended daily allowance
Total Protein (grams) 3.97 4.96
Amino Acids
Arginine (g) 0.19 0.19
Histadine (g) 0.064 0.064
Isoleucine (g) 0.11 0.11
Leucine (g) 0.25 0.25
Lysine (g) 0.067 0.084
Methionine (g) 0.033 0.042
Methionine (g) 0.067 0.084
Phenylalanine (g) 0.099 0.099
Phenylalanine-tyrosine (g) 0.38 0.38
Taurine (g) 0.0079 0.0099
Threonine (g) 0.13 0.13
Tryptophan (g) 0.032 0.032
Valine (g) 0.13 0.13
Fats
Total Fat (g) 2.2 2.2
Linoleic Acid - Omega 3 (g) 0.14 0.14
Arachidonic Acid - Omega 6 (g) 0.0005 0.0015
Eicosapentaenoic & Docosahexaenoic Acid (g) 0.0025 0.0025
Vitamins
Vitamin A (µg) 19.8 24.7
Vitamin D3 (Cholecalciferol) (µg) 0.14 0.17
Vitamin E (alpha tocopheral) (mg) 0.74 0.94
Vitamin K (menadione) (mg) 0.025 0.025
Thiamin (mg) 0.11 0.14
Riboflavin (mg) 0.079 0.099
Pyridoxine (B6) (mg) 0.05 0.06
Niacin (B3) (mg) 0.79 0.99
Pantothenic Acid (B5) (mg) 0.11 0.14
Folic Acid (B9) (µg) 15 19
Biotin (B7) (µg) 1.5 1.9
Vitamin B12 (Cobalamine) (µg) 0.44 0.56
Choline (mg) 60 63
Vitamin C (mg) 0 0
Minerals
Calcium (g) 0.040 0.071
Phosphorus (g) 0.035 0.063
Potassium (g) 0.13 0.13
Sodium (mg) 16.0 16.7
Chloride (mg) 23.7 23.7
Magnesium (mg) 4.9 9.5
Iron (mg) 1.98 1.98
Copper (mg) 0.119 0.119
Iodine (µg) 31.6 35
Zinc (mg) 1.9 1.9
Manganese (mg) 0.119 0.119
Selenium (µg) 6.95 6.95

See also

Abnormalities of eating

Dietary related diseases

References

  1. Dr Jim Euclid pers comm
  2. Malik, R (2009) Pers Comm with Euclid, J
  3. Hill's Adult Original Feline Optimal Care, Hill's, USA
  4. Pibot, P et al (2008) Encyclopedia of Feline Clinical Nutrition. Royal Canin, France.
  5. August, JR (2006) Consultations in feline internal medicine. Vol 5. Elsevier Saunders, USA
  6. Vester BM, Burke SL, Liu KJ, Dikeman CL, Simmons LG, Swanson KS. (2010) Influence of feeding raw or extruded feline diets on nutrient digestibility and nitrogen metabolism of African wildcats (Felis lybica) Zoo Biol Jan 21
  7. Verbrugghe A & Bakovic M (2013) Peculiarities of one-carbon metabolism in the strict carnivorous cat and the role in feline hepatic lipidosis. Nutrients 5(7):2811-2835
  8. MacDonald ML et al (1984) Nutrition of the domestic cat, a mammalian carnivore. Annu Rev Nutr 4:521-62