Cats require some nutrients that are not essential for other mammals. Many of these essential nutrients are found naturally in animal tissues, reflecting that cats have developed specialised nutrient requirements consistent with the evolutionary influence of a strict carnivore (MacDonald et al., 1984).
In addition, in feeding cats, the nutritional composition and the palatability of the diet are crucial. If unpalatable, cats will refuse to eat and consequently may become deficient in essential nutrients, which may develop into clinical conditions (Zaghini & Biagi, 2005). This highlights the importance of formulating and feeding highly palatable, nutritious diets for cats.
Lipids constitute a group of organic molecules, which include fats and oils. Dietary lipids are a source of essential fatty acids and concentrated energy since fat provides twice the amount of calories/g compared to protein and carbohydrates. Lipids have an important role as carriers for fat-soluble vitamins and sterols and are components of many hormonal precursors. Additionally, they are utilised to improve dry kibble’s palatability and textural properties (Trevizan & Kessler, 2009).
Fatty acids are integral components of lipids. The essential nature of a fatty acid is primarily due to an animal’s inability to synthesise it in sufficient quantities to meet its metabolic needs (Bauer, 2008). Cats, like dogs, require the essential fatty acid linoleic acid. Linoleic acid is a polyunsaturated omega-6 fatty acid. Fatty acids can be elongated and desaturated into alternative, longer-chained fatty acids. For example, dogs readily convert linoleic acid into arachidonic acid by the enzyme Δ6-desaturase. However, cats are unable to do this as conversion is limited due to the low activity of the enzyme Δ6-desaturase in the cats’ liver. As a result, arachidonic acid is an essential fatty acid in cats and must be obtained in the diet. Arachidonic acid is found in an abundant supply in animal tissues, especially the organs (Trevizan et al., 2012). This reinforces the requirement for cats, as obligate carnivores, to consume animal tissues in order to meet their nutritional needs.
Vitamins are organic compounds only required in small quantities and are classed as essential micronutrients. As they are not endogenously synthesised, they must be obtained from the diet. Vitamins have diverse biochemical functions, which are required for the maintenance of normal health and metabolic integrity. The dietary requirements of cats for specific vitamins differ from those of most other mammals. These particularities result from significant differences in enzyme activities during the synthesis of niacin (vitamin B3) and vitamin A (NRC, 2006).
Dietary niacin is essential in cats as niacin (and associated compounds including nicotinic acid and nicotinamide adenine dinucleotide, NAD) plays a fundamental role as coenzymes in the metabolism of carbohydrates, Amino acids and ketone bodies in cats. Cats, unlike dogs, cannot synthesise significant levels of niacin from the essential Amino acid tryptophan. This is due to a very high activity level of an enzyme (picolinic carboxylase) that rapidly converts a metabolite of tryptophan to form acetyl-CoA rather than niacin, resulting in insufficient production of niacin. As a result, the niacin requirement of cats is 2.4 times higher than that of dogs (NRC, 2006).
Similarly, cats require dietary, pre-formed vitamin A. Vitamin A is essential for vision, cellular differentiation and immune function in cats. Carotenoids, for example, β-carotene, are precursors for vitamin A. They are synthesised by plants and, therefore, are commonly found in vegetables, such as carrots and sweet potatoes. In comparison, animal tissue contains relatively low concentrations of carotenoids and adequate amounts of vitamin A. As obligate carnivores, cats lack the enzyme required to produce vitamin A from β-carotene, and although they can absorb β-carotene, they cannot convert it to vitamin A (Schweigert et al., 2002). Dietary pre-formed vitamin A is only essential in cats, as dogs have the enzymes essential for converting carotenoids (Zaghini & Biagi, 2005).
As obligate carnivores, cats rely heavily on nutrients readily found in animal tissues. It is important cats are fed high-protein diets that contain essential Amino acids. In addition to the essential Amino acids shared with dogs, cats require taurine, which is found in animal-origin ingredients. High concentrations of essential fatty acid arachidonic acid found in animal tissue reinforce this requirement for nutrients, specifically in animal products. Finally, cats require dietary vitamins that other mammals can endogenously synthesise. Examples of these include niacin and preformed vitamin A.
Article written by Charlotte Stainer