Royal Canin Nutritional Information

8. Royal Canin Nutritional Information

Focus on: Long-chain omega-3 fatty acids (EPA-DHA)

Omega-3 fatty acids are a separate family of polyunsaturated fatty acids (PUFA). Their precursor is a-linolenic acid (C18:3, n-3), whose chemical structure distinguishes it from linoleic acid (C18:2, n-6), the precursor of the other main family, omega-6 fatty acids. Linoleic acid is an essential fatty acid for cats, which depend on a dietary intake to cover their requirements. With the exception of docosahexaenoic acid (DHA), the omega-3 series of fatty acids are not considered to be essential, as cats can survive with a food that does not contain them. On the other hand, their health may benefit from their introduction in the diet.

Figure 12. Linoleic acid: C18:2 (n-6); omega-6 fatty acid precursor.

Figure 13. α-linoleic acid: C18:3 (n-3); omega-3 fatty acid precursor.

Metabolism of Unsaturated Fatty Acids

The synthesis of long-chain fatty acids is triggered by the action of enzymes in the liver (desaturase and elongase), which add to the carbon atoms and the unsaturated double bonds. These are the same enzymes that act in the synthesis of omega-3 and omega-6 fatty acids, which explains the competition between the two families.

In cats, the enzyme responsible for the first desaturation, D6 desaturase, has a very low-level of activity (Sinclair et al., 1979; Pawlosky et al., 1994).
- In the series of omega-6 fatty acids, D6 desaturase produces very low quantities of arachidonic acid. In the absence of dietary intake a healthy adult cat may be able to cover its requirements, but gestating queens will produce no or few viable litters and the proportion of cannibalism appears to be higher (Morris, 2004). Arachidonic acid is therefore deemed essential in cats, contrary to dogs.
- With respect to omega-3 fatty acids, the yield from a-linolenic acid (omega-3) is very low. Likewise, the enzyme activity responsible for interconversion from its omega-6 homolog (DHA: C22:5) has only been shown in the brain in cats (Pawlosky et al., 1994). Therefore, when EPA-DHA supplementation is recommended, they should be provided preformed in the food.

Figure 14. Hepatic synthesis of long-chain omega-3 and omega-6 fatty acids from their respective precursors.

Sources of Omega-3 Fatty Acids

Some vegetable oils, such as soy oil and especially linseed oil, contain a non-negligible quantity of a-linolenic acid. In contrast, oils sourced from the sea are the only useful sources of EPA and DHA.

PUFA sourced from the sea are synthesized in the chloroplasts of phytoplankton or micro-algae consumed by fish. Higher up the food chain, some fish incorporate omega-3 PUFA and their metabolism transforms them until the fatty acids contain 20 - 22 carbon atoms. EPA and DHA are especially concentrated in the adipose tissue of fish. Fish oils (especially cold sea fish like salmon, mackerel, anchovy, halibut and herring) can contain more than 30% EPA-DHA.

Key points to Remember about: Nutritional Management of Hyperlipidemia

1. Give the cat a low-fat diet: 
   < 30 g/1000 kcal or less than 10% fat in a 4000 kcal/kg food:
   - In the event of obesity, weight loss is indicated to lower the cholesterol concentration;
   - When the body condition is optimal the low-fat diet may need to be supplemented with calories compared with a maintenance food to avoid undesirable weight loss.
2. When the low-fat diet is inadequate to control hyperlipidemia, fish oil (10 - 200 mg/kg), which is rich in the long chain omega-3 fatty acids EPA and DHA, can reduce serum lipid concentrations.
3. Adding a large quantity of unsaturated fatty acids (omega-3) increases the risk of oxidation of the lipid membranes.The administration of biological antioxidants (e.g., vitamin E, vitamin C and beta-carotene) can limit the oxidative reactions.

The adaptation of the cat’s metabolism to a carnivorous diet is especially expressed by the specific requirements of essential fatty acids, which differ from those of the dog. (© Y. Lanceau/Royal Canin/Birman).