From The October 2001 Issue of Nutrition Science News
By C. Leigh Broadhurst, Ph.D.
Oils cats and dogs need for healthy skin and coats
Dogs and cats suffer from many problems that affect their skin and coats. Skin, the body's largest organ, is a natural protector against toxic substances, dehydration, infection, and ultraviolet light. Good nutrition can have a positive effect on an animal's coat and skin.
The pet food industry did $8.9 billion in sales in 1999 and grew at a rate of 4.6 percent over the previous year. The naturals pet food category, which contains many nutrients and supplements not found in generic food, did $22.4 million in sales in 1999relatively small, but up 38.9 percent over the previous year, according to A.C.Nielsen data. Frost & Sullivan estimates that 217,300 pounds of nutritional ingredients were used in pet foods in 2000. Within this category, one ingredient that is poised for growth is polyunsaturated fatty acids (PUFAs).
Polyunsaturated means a fatty acid has two or more double bonds in its chain of carbon atoms. In contrast, saturated fatty acids have no double bonds, and monounsaturated fats have just one double bond. All mammals produce their own saturated and monounsaturated fats, but not PUFAs. But are all PUFAs essential, or just the dominant two essential fatty acids, linoleic and alpha-linolenic?
There are two distinct PUFA families, n-6 and n-3 (also known as omega-6 and omega-3). Linoleic acid (LA) is the head of the n-6 family; the important n-6 derivatives of LA are gamma-linolenic acid (GLA) and arachidonic acid (AA). Alpha-linolenic acid (LNA) is the head of the n-3 family; the important n-3 derivatives of LNA are eicosa-apentaenoic acid (EPA) and docosahexaenoic acid (DHA). When mammals eat oils or foods that contain LA or LNA, it's theoretically possible for enzymes in their bodies to convert these fatty acids to longer-chain fats with more double bondsLC-PUFAs. But in reality, full conversion to LC-PUFAs is an inefficient process.
This crucial point has enormous bearing on which fats are essential for dogs and cats.
Essential PUFAs For Dogs
Dogs are carnivores but thrive as omnivores as long as their diet is mainly meat-based. Unlike cats, domestic dogs have become dependent on humans to provide food for them.  Consequently, dogs' diets tend to contain high levels of carbohydrates. Their essential amino acid requirements are roughly similar to humans. In addition, canines can make vitamin A from beta-carotene, but the extent to which they do so depends on age, breed, and health. Vitamin A deficiency is rare in companion animals, and a toxicity state, with its accompanying skeletal changes, is more likely to occur.
Logically, canine PUFA metabolism reflects their carnivore-omnivore status. With respect to n-6 PUFAs, both LA and AA are essential for dogs. Canines apparently convert LA to AA more readily than humans do.  Therefore, dogs do not benefit from large quantities of vegetable oils rich in LA; in fact, this may exacerbate allergic and inflammatory conditions. Vegetable oils are not prevalent in the natural canine diet. 
Canned dog food and meat are rich in AA and typically provide adequate levels of LA. In some cases, a dog may need additional LA. For example, dogs fed bargain brands of low-fat, dry dog food are more likely to suffer LA deficiencies.  Symptoms can include dry, dull coat and skin, excessive shedding, itching, unsuccessful breeding and digestive problems. These are mainly symptoms of overall fat and/or PUFA deficiency, not just LA. Another scenario likely to produce EFA deficiency is home-prepared diets. Dogs fed human food receive too many carbohydrates and trans-fats, and perhaps not enough PUFAs. If required, LA is easily supplied with one to two tablespoons of vegetable oil such as flax, safflower, soybean, or sunflower mixed in food daily.
Canines metabolize n-3 and n-6 differently. Dogs fed ground flaxseedswhich contain about 55 percent LNA and 45 percent LA, and is one of the richest sources of LNAshowed ability to convert LNA to EPA and to docosapentaenoic acid (DPA) as confirmed by blood tests, but not to DHA.  At least some preformed DHA is required for optimal canine nervous system function and visual development as well as for effective reproduction.  DHA concentrates in the eye and is critical for vision. Retinal degeneration is a leading cause of blindness in companion animals. Some breeds have an inherited tendency to develop this condition, which may be related to abnormalities in LC-PUFA metabolism.  For example, miniature poodles with genetic retinal degeneration were found to have abnormally low ratios of DHA to DPA in the eye tissue and bloodstream.  It may be that DHA is indeed made in the retina but not enough to be optimal. And if transport is indeed suboptimal, it may make sense to increase the amount of DHA available just to try to alleviate the problem somewhat. Certainly, if transport of DPA is impaired, supplementing DHA makes good sense.  (This is still an active area of research.)
John Bauer, D.V.M., Ph.D., of the Department of Small Animal Medicine and Surgery at Texas A&M University, recommends that aging dogs, and breeds known to be susceptible to visual defects, receive DHA supplements. 
In nature, canines acquired DHA by eating organ meats and their associated fat deposits, bone marrow, and occasionally fish and reptiles. The modern processed diet, especially one based on dry, low-fat dog food, may not provide adequate DHA. This is especially true for breeding females and puppies. Based on the sum of research, Bauer recommends a serving of fatty fish or one to two tablespoons fish oil every two to three days.
Although LNA is not considered essential for canines, one to two tablespoons of flaxseed oil per day can give healthy dogs more lustrous coats.  Dog, horse and sheep breeders have added flaxseed to feed for years to improve animal coat condition, though the mechanism of action was not known. Australian researchers for the first time may have found the answer. Working with guinea pigs, the researchers fed the animals LNA that could be traced and observed that LNA was deposited intact on the surface of their hairs. 
Refined, processed canola and soybean oils are not good sources of LNA because seed varieties with low levels of LNA are grown for oil pressing, and the remaining LNA is further destroyed during processing.  Cold-pressed, unrefined flaxseed oil is a more reliable source of LNA.
PUFAs For Pussy Cats
Unlike domestic dogs, house cats have retained their hunting instincts and are not entirely dependent on humans for food. Kittens without human contact revert to feral behavior and cannot be socialized as adults. Cats are obligate carnivores, meaning they must eat meat, fish, reptiles, amphibians, and birds to live and reproduce.  As such, felines have specific metabolic differences from humans and dogs. 
Cats cannot make vitamin A from beta-carotene and require preformed vitamin A from animal sources.
Felines metabolize carbohydrates poorly and can neither tolerate nor thrive on a high-carbohydrate diet.
Cats have high protein requirements but cannot easily replace protein in the diet with other energy sources to conserve body protein. In starvation conditions, cats waste their own muscles in a matter of days.
The amino acids arginine and taurine are essential for cats. Lack of these in the diet rapidly causes blindness and death. Only animal protein provides arginine and taurine at the levels cats require.
Naturally, feline PUFA metabolism is strictly carnivorous. Cats do not eat fruit, vegetables, nuts, or seeds in their natural diet and have no need for vegetable oils, either. Cats lack some of the enzymes that enable humans and dogs to convert LA to LC-PUFAs. Because cats cannot synthesize AA, their daily requirement for AA is so high that it must be provided in the diet. 
Cats need only a small amount of LA (less than humans or dogs), but a normal diet supplies it and there is no need to supplement. Cats cannot make GLA from LA, but they do not seem to need much. However, GLA is helpful for cats with skin and coat problems.  Show cats and long-haired cats may also benefit from GLA. Squeeze a 500 to 1,300 mg capsule of borage or evening primrose oil into moist food daily or every other day, or use an oil blend as described below.
DHA is critical for cats, but they cannot make it from LNA because of the same reasons they cannot convert LA to LC-PUFAs.  Kittens born to cats deprived of DHA may have visual and some nervous system defects.  Fish oil is the only currently acceptable n-3 PUFA supplement for cats. Algal DHA may be effective, but it is expensive and has never been tested on cats. Also, vegetable matter is not part of a cat's normal diet, and algal DHA has no EPA, which could be important. Cats fed dry food or rarely fed fish may be in need of n-3 LC-PUFAs. DHA deficiency quickly reduces a cat's vision, immunity, and breeding performance. [8,11,17] Cats also suffer from hereditary and age-related retinal degeneration, conditions linked to reduced retinal DHA levels.  I recommend mixing one to two tablespoons fish oil or a fish oil and borage/evening primrose oil blend with moist cat food daily.
Pet Foods And PUFAs
Pet owners cannot rely on commercial pet foods to supply adequate PUFA levels. This is especially true of dry, low-fat pet foods and "bargain" brands. High-quality fish flavors of canned cat food are the best source of essential PUFAs. This is one reason why cats do not develop coat and skin conditions as often as dogs do. However, not getting enough LC-PUFAs adversely affects cats' immune systems and eyesight faster than in dogs because they can't make the enzymatic conversions. 
More expensive, premium pet foods generally meet n-6 PUFA requirements, but not all brands contain adequate n-3 PUFAs. Owners should consistently feed their pets both fresh raw meat (especially organ meat) and fish. A cat's desire to hunt is not only instinct but, some people believe, is also because they crave the nutrients in fresh, raw game meat that are lacking in their diets.
It is important that pets receive supplementation with a broad range of antioxidants in addition to PUFAs. Cats in particular have high vitamin A and E requirements relative to humans and dogs. Working together, antioxidants such as vitamins A and E, selenium, and many herbal phytochemicals prevent PUFAs from oxidizing. Unlike humans, dogs and cats make their own vitamin C, so supplementation is necessary only when the animal is under stress, and doses are much lower than used for humans.
Foods Rich In PUFAs
Healing Skin And Coat Conditions
C. Leigh Broadhurst, Ph.D. heads 22 [nd] Century Nutrition, a nutritional/scientific consulting firm, and is author of Diabetes: Prevention and Cure (Kensington, 1999).
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