Fats, Pets and Health

Discussions of the role of fat in the human diet has held the interest of both the popular press and the scientific community for many years. Coronary heart disease is the leading cause of death in the United States and is a major health problem in developed countries (Surgeon Generals Report, 1988). The relationship between coronary heart disease in humans and high fat diets has given fat a negative image for the energy rich human diet.

Fat is an essential ingredient in the diet of all species and maintaining sufficient quality fat is an important consideration in the lower fat normal diets of dogs and cats. Dietary fats are caloric dense ingredients that provide an important source of essential fatty acids and fat soluble vitamins (A, D, E, and K).

Young animals need dietary fat and cholesterol for growth and to maintain proper health. Adult dogs and cats require essential fatty acids in the diet to sustain metabolic and physiologic functions. The importance of fat type and quality in the diet of companion animals will be discussed including some of the most recent research in dietary fatty acid manipulation for improved health.

Fats are commonly composed of three fatty acids attached to a glycerol skeleton resulting in the name triglycerides. The fatty acids that must be supplied in the diet of dogs and cats are called essential fatty acids.

Linoleic and alpha-linolenic acid are two essential fatty acids for dogs and cats because of the lack of enzymes needed to synthesize these fatty acids and they therefore must be provided in the diet.

Arachidonic acid is another fatty acid which is essential to cats as they lack an enzyme (delta-6-desaturase) needed to synthesize this fat in their bodies. Arachidonic acid is a constituent of animal fats but is not present in any vegetable oils.

Deficiencies of essential fatty acids are far reaching because of the role that essential fatty acids play as necessary constituents of cell membranes, particularly in controlling epidermal loss of water.

Essential fatty acid deficiency may result in impaired reproductive efficiency, impaired wound healing, a dry lusterless coat and scaly skin predisposing the pet to skin infections (pyoderrna). If the deficiency persists, exudation from a localized area of the skin may lead to a moist dermatitis. These lesions are common in the external ear canal and between the toes although they may develop other places on the body resulting in "hot spots".

Essential fatty acid deficiency is rare in companion animals today but occurs in dogs or cats receiving low-fat, dry dog foods containing beef tallow, or dry foods that have been stored too long resulting in oxidation of the dietary fats.

Although essential fatty acid deficiency does not commonly occur, dietary manipulation of essential fatty acid metabolism does appear to have efficacy in treating a number of different conditions including treatment of skin disorders that are not the result of a dietary deficiency of essential fatty acids.

Essential fatty acids are identified by their chemistry, in particular the distance of the first double bond in their carbon chain from the ten-ninal methyl group. The omega 6 group of essential fatty acids have their first double bond 6 carbons from the methyl end while the omega 3 group of essential fatty acids have their first double bond 3 carbons from the methyl end.

Vegetable oils are high in omega 6 fatty acids but tend to oxidize quickly leading to the need for higher levels of antioxidants in the food. Fats from species like poultry are higher in omega 6 fatty acids than other animal fats like beef tallow and tend to be much more stable than vegetable oils.

The ratio of omega 6 to omega 3 fatty acids in the diet is of particular research interest currently. Land animals tend to have high levels of omega 6 fatty acids in their diet as most plants contain higher amounts of omega 6 fatty acids than omega 3 fatty acids. Corn, soybean, sunflower and safflower are oils high in omega 6 fatty acids. Studies indicate that high levels of omega-6 fatty acids reduce immune competence. Algae synthesize high amounts of omega 3 fatty acids and as a result most marine animals contain high amounts of omega 3 fatty acids.

The ratio of omega 6 to omega 3 fatty acids in an animals tissue can be manipulated through dietary means influencing hormone messengers called eicosanoids which influence the inflammatory response.

Research with dogs shows that diets with omega 6 to omega 3 ratios of 5: 1 to 1 0: I reduced the inflammatory response in the dog's skin. As most dietary fats of non-marine origin are much higher in omega 6 fatty acids than omega 3, finding stable sources of omega 3 fatty acids has been a priority. Flax is a Canadian grown oil seed with higher levels of omega 3 fatty acids and is now being used to correct fatty acid profiles to achieve the 5-10:1 ratios.

Allergic skin responses are common in dogs with many dogs reacting to common antigens in the environment. Inhaled allergens such as pollens or molds are the most common culprit although certain food components, external parasites, chemicals and topical irritants may also cause allergic reactions. Dietary manipulation of the fatty acid profile of the diet is one treatment for allergic dermatoses in dogs and cats.

Although flax contains the omega 3 fatty acid alpha-linolenic acid, other dietary ingredients such as borage oil, evening primrose oil and black currant oil containing gamma-linolenic (an omega 6 fatty acid produced after the delta-6 desaturase step) are also used to change fatty acid profiles and impact physiological function leading to long term control of skin disease.

As documentation on appropriate doses of fatty acid supplementation to provide a noninflammatory lipid base is limited and may interfere with anti-inflammatory drug therapy, it is important to seek veterinary assistance when supplementing diets with high levels of fatty acids.

Dietary fats are important constituents of the diets of dogs and cats as they are essential dietary constituents, energy dense, play a role in the health of the animal and increase the palatability of the diet. The dietary fats chosen for dog and cat foods are chosen for their fatty acid profile, stability and palatability. Although precise requirements for essential fatty acids have been researched, ratios of essential fatty acids in the diet have been shown to have effects beyond their minimal dietary requirement.

New animal and fat sources will continue to be developed as more research leads to a better understanding of the exact role fats play in companion animal health and welfare.

by David Dyble B.Sc., M.Sc., P.Ag. Nutritionist