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Antioxidants in canine food
Sometimes owners are raising the question whether antioxidants are necessary in pet food and which were the best. This excellent article gives a summary about the different antioxidants, their mode of action and the role of oxygen and free radicals.

Antioxidants are major defense system against minimizing damage from free radical scourge and oxidative stress.

Oxygen gives pets life but may behave aggressively to try to shorten it.

Without sufficient oxygen, a pet`s tissues are in immediate jeopardy. Ironically, excess oxygen can poison the cells of a pet`s body via free-radical formation-what a dichotomy!

Normal compounds stabilize their chemical bonds by sharing electrons, one from each atom. Highly unstable free radicals steal an electron from normal compounds (typically oxygen), producing a stable compound by pairing their unpaired electron. In doing so they alter the stable compound, creating another free radical, again short one electron, continuing the chain. This chain reaction creates havoc in the cell.

Free radicals are commonly produced as part of normal cell metabolism, but also can become excessive following injury, disease, or due to environmental pollutants such as UV radiation, cigarette smoke or smog.

Excessive free radical production or oxidative stress results when the formation of free radicals overwhelms the body`s defense system against them producing an imbalance between production and removal of free radicals. Oxidative stress can overpower the pet`s ability to fight back and may result in cell and tissue damage, thus shortening its life, just like oxygen can brown an apple or banana.

Run amok
Uncontrolled free radicals may run amok throughout a pet`s body, doing considerable damage to cells.
They alter the structure of cell membranes, and create havoc to polyunsaturated fats, cell proteins and cell DNA. The more active the cell, the greater the potential risk of tissue damage.

In people, this damage has recently been linked to degenerative diseases such as rheumatoid arthritis, cancer, cardiovascular disease, inflammatory bowel disease, renal disease, Parkinson`s Disease, cataracts, and may have a deleterious affect on aging. It is thought that free radical damage may play a similar role in certain diseases of pets and wreak havoc on the aging process (Freeman, et al 1999; Toll et al, 2001).

Antioxidants to the rescue
Antioxidants are the pet`s major defense system against the scourge of free radicals and oxidative stress, keeping their damage to a minimum.

Dietary antioxidants, like vitamin E, scavenge and convert free radicals to relatively stable compounds and stop or prevent the chain reaction of free radical damage. Antioxidants are therefore important to protect pets from tissue damage, disease and may in the process, enhance immunity.

Endogenous enzymatic antioxidants, including superoxide dismutase and glutathione peroxidase, are one line of defense against free radicals.

Dietary antioxidants include vitamin E, vitamin C, taurine, and the carotenoids - beta-carotene, lutein, and lycopene and certain trace minerals. These antioxidants gobble up free radicals, stopping them in their tracks.

Antioxidants keep the pet`s cells healthy, including lungs, heart, blood cells, muscles, nerves, GI tract, and reproductive organs. It was recently demonstrated that a cocktail of such antioxidants limited cell damage in dogs and cats (Heaton et al, 2001).

Geriatric success
Currently work is being done to show the benefits of antioxidants to older pets` ability to learn, to modify certain behavior problems and function better in their geriatric years (Milgram et al, 2001).

The potential role of dietary antioxidant therapy to benefit diabetes, renal disease and feline asthma has been proposed (Harper 2000). It has been suggested that the addition of various antioxidants improves the antioxidant status of elderly dogs. (Zicker, 2001).

Vitamin C
Vitamin C (ascorbic acid) is a powerful water-soluble antioxidant.

It regenerates vitamin E, glutathione, and flavonoids; reduces free radicals in cells; and works with minerals in their role as antioxidants.

It is also thought to destroy free radicals involved in carcinogen metabolism. High activity dogs, those competing in flyball, agility, racing and high-demand rescue work are thought to require increased amounts of vitamin C due to the increased demand of oxidative stress (Baskin et al, 2000; Piercy et al, 2000).

Although the dog can synthesize vitamin C, racing and other forms of high-energy exercise are thought to increase the demand for all antioxidants to combat increased oxidative stress with increased body use of oxygen (Marshall et al, 2001). Unlike humans and guinea pigs, the dietary vitamin C requirement of cats is negligible, because they can synthesize it, though their need for vitamin C, as an antioxidant is unexplored. Surely the benefit of vitamin C as an antioxidant is feasible.

Carotenoids are red, yellow, and orange fat-soluble pigments found in plant foods such as carrots and tomatoes. Though the dog and cat are predominantly carnivores, the value of these powerful antioxidants could be important to assist them. We don`t yet know all the benefits of these compounds to dogs and cats to prevent degenerative diseases, cancer and combat conditions of aging. Studies have shown that cats do readily absorb beta-carotene across the intestinal mucosa (Chew et al, 2000).

It has been shown that dietary lutein stimulated both cell-mediated and humoral immune responses in dogs (Kim et al, 2000). Since dogs and cats are living longer today, carotenoids may benefit in ways yet undiscovered.

Taurine, an amino acid, is a critically important nutrient for cats. Its benefit is for successful reproduction, healthy eyesight and heart function.

Though important to cats, taurine is not similarly essential to dogs. For dogs and cats taurine is beneficial as an antioxidant, known to protect cell membranes from damage.

Certain minerals, especially zinc (Zn), copper (Cu) and selenium (Se) and manganese (Mn) are antioxidant minerals.

They occur in the structure of specific enzymes that are integral parts of various enzymatic antioxidants in the pet`s body.

Zinc and copper are in superoxide dismutase as well as other enzymes, and selenium is in glutathione peroxidase. These enzymatic antioxidants are equally important as dietary antioxidants consumed by pets.

Vitamin E (alpha-tocopherol)
Vitamin E is unique among vitamins. As alpha-tocopherol, vitamin E is notably essential for the proper function of the reproductive, muscular, nervous, circulatory and immune system. Its antioxidant property is its prime function. Vitamin E, which can`t be synthesized in a pet`s body, is possibly the most important and essential antioxidant, protecting cell membranes from free radical damage by preventing lipid peroxidation of unsaturated fatty acids.

Vitamin E is especially necessary to newborn kittens and puppies, since placental transfer is poor, first milk, colostrum is important to provide adequate vitamin E. Vitamin E works in concert with other antioxidants, including vitamin C, carotenoids, and mineral-containing enzymatic antioxidants.

Vitamin E may also work synergistically with taurine (Carnevale, Hintz, and Schryver, 1988, personal communication).

Vitamin E absorption, transport, and utilization begin with its uptake in the small intestine.

Vitamin E is absorbed with a mixture of dietary fat sources, primarily triglycerides, through the small intestine, with the assistance of bile and pancreatic fluids. It is moved via the lymphatic pathway to the liver in association with chylomicrons. Once vitamin E reaches the liver, it is transported to peripheral tissues in the blood bound to lipoproteins (VLDL, LDL, HDL).

The majority of vitamin E is found in adipose tissue, the rest is primarily found in the liver and skeletal muscles. There is considerable vitamin E present in lung and spleen.

Natural E differs from synthetic E
Usually synthetic vitamin sources are, for the most part, equal in efficacy and structure to the natural form of the vitamin, such is the case of vitamin C. Not so for vitamin E. The source of vitamin E with the highest biological activity is natural vitamin E (d-alpha-tocopherol) isolated from seed oils. Synthetic vitamin E (dl-alpha-tocopherol) is made from petrochemicals (Figure 3, p. 24S). The body preferentially transports and incorporates natural vitamin E. Synthetic vitamin E is not as biologically potent in comparison. The difference between natural and synthetic is in the chemical structures of the two.

Source: Ed Kane (2004): Dietary antioxidants are important for pets. In: DVM Newsmagazine February 1, 2004

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Reference intervals for blood parameters in Shetland Sheepdogsmembers
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