Bryan G. Miller
Every dog food has vitamins and minerals added to make it just right for proper dog nutrition. The technical term for most of the nutrients which the body requires in small amounts is “micronutrients.” These nutrients are required in the correct amounts and balance to maintain good health and vitality.
Because of the information which labels are required to show, many of us check out the amounts of protein, fat, fiber, and the macro-minerals calcium and phosphorus in the dog food we buy.
Many pet owners are well educated as to requirements and the best sources of these important nutrients. It is certainly a positive sign that many consumers are now carefully reading labels to compare these important nutrients when making buying decisions.
Unfortunately, most of us know much less when it comes to the sources and amounts of the micronutrients. Vitamins and minerals are also required for good health, and like protein and fat sources, there are better and worse sources of vitamins and minerals.
It’s nearly impossible to evaluate every vitamin and mineral in a dog food. However, it helps to know how to separate nutrition from “sales-hype.” The following are only some of the most commonly confused items.
Vitamins are small organic molecules that are required as “cofactors” in many metabolic reactions. They are generally characterized as either fat-soluble or water-soluble. The fat-soluble vitamins are A, D, and E; the water-soluble vitamins are the B vitamins. Vitamins are a relatively inexpensive part of the diet and most companies will provide a vitamin level in excess of AAFCO recommendations.
Today’s commercial sources of Vitamins A, D, and E are much more stable than forms from years past. That means your dog is more likely now to get all the vitamins he needs from his food.
Performance category dog foods, are high in fat to give high-performance dogs more energy. Likewise, these foods should contain greater amounts of the fat-soluble vitamins than similar foods of lower fat content. In addition, more Vitamin E may be used to compensate for the greater need of fat metabolism. This is especially true if the food contains fat which is high in polyunsaturates.
Vitamin A. Vitamin A is usually found as Retinyl Acetate. Most commercial sources are “packaged” in small gelatin beadlets which help extend shelf life by avoiding oxidation. Quite often, Vitamin A is combined with Vitamin D in these gelatin beadlets.When the food is made, the beadlets are mixed in.
Vitamin D. Vitamin D is added to food in the form of either Vitamin D3, Cholecalciferol, or Vitamin D2, Ergocalciferol. Both forms appear to be equally well-absorbed and active. Current Vitamin D products are quite stable.
Vitamin E. Alpha-tocopherol is the most biologically active form of Vitamin E. It’s available from natural sources or synthetic.
The all-natural sources have more activity per gram of Vitamin E; however, the synthetic forms may be more active. Vitamin E is a relatively expensive vitamin and it may be worth asking for activity levels when talking to manufacturers’ representatives. (New evidence points to a greater importance of Vitamin E in proper immune system function. Because of its high cost, most manufacturers don’t “overload” Vitamin E. Generally speaking, more E is better.)
More and more companies have been using tocopherols as additives to help prevent oxidation (rancidity) of fats in dog food. These tocopherols don’t add significantly to the Vitamin E content available for use by your dog’s body.
Water-soluble B vitamins are generally susceptible to degradation, particularly in foods with high mineral and water content. This is one of the reasons you should select fresh bags of dog food as opposed to old inventory. Shop where the product has not been in storage for many months, and check the production code to determine when the food was made.
Although there are many B vitamins, you should consider the following three when selecting foods.
Thiamin. Thiamin is important for energy metabolism. Commercially, it is available as either Thiamin mononitrate or Thiamin hydrochloride. Both forms are active; however, thiamin mononitrate has a much greater shelf life.
Vitamin C. Vitamin C, ascorbic acid, has not been proven to be a necessary supplement for dogs. (Dogs make their own.) The addition of Vitamin C at this point may be more from a marketing point of view than a nutritional one. However, if you do want a food with Vitamin C, look for one containing ascorbyl polyphosphate.
Vitamin C is extremely easily oxidized (which is its biological function, as well), and does not survive processing well. Within two months of processing, most of the “normal” Vitamin C will have naturally decayed away. The new polyphosphate forms are stable, and biologically active, but they are expensive.
Choline. Choline is required and important for the proper utilization of the sulfur-containing amino acids. Current recommendations are for 25 mg per kilogram of body weight in adults and 50 mg per kilogram of body weight for puppies. Choline should not be fed in great excess as it greatly increases the breakdown of the other vitamins.
Like vitamins, trace minerals are important cofactors in order for many enzymes to function. Trace minerals include copper, iron, zinc, manganese, iodine and selenium. Trace mineral nutrition is difficult to study due to the many interactions between trace minerals and other components of the diet and the many interactions between the trace minerals themselves.
Trace mineral nutrition is often blamed for poor coat appearance and color. Trace minerals can have an effect upon coat quality, as can a great many other nutrients in the diet.
Measuring trace mineral content of hair, blood, and plasma samples does not always provide an accurate appraisal of trace mineral nutrition. If you truly believe your dog has a mineral imbalance, have a liver biopsy done. It’s the best measure of current mineral status.
Trace minerals are available from inorganic sources such as oxides, carbonates and sulfates. Availability can vary with the source of the mineral. Generally speaking, sulfates are more available than carbonates, which are more available than oxides. Iron oxide has no biological activity but is sometimes added as a coloring agent. The major exception is zinc oxide, which is the most common form of supplemented zinc.
Be wary of any dog food that claims to have much greater concentrations of any one mineral. Because of the way in which trace minerals are absorbed and stored, an excess of one trace mineral may lead to either a deficiency or toxicity of other amino acids.
Some breeds have different mineral requirements, the most notable being Bedlington Terriers, which are susceptible to copper toxicity.
Many of the trace minerals are now also available attached to organic com-pounds in the form of chelates and proteinates. Trace minerals are often absorbed in connection with amino acid absorption. Most of the chelated products involve the attachment of the trace mineral to either an amino acid or a small protein molecule, although there are also polysaccharide complex products marketed as well.
Improved availability in the form of chelates and proteinates has not been conclusively proven. However, they probably help to reduce vitamin oxidation by preventing the interactions between vitamins and the trace minerals. Chelates (zinc-methionine, for example) are much more expensive than their inorganic counterparts.
If a manufacturer is using chelated minerals, be sure that they are supplied at a level of mineral (grams of mineral) equal to the requirement as established in research using inorganic forms. Improved bioavailability has not been conclusively proven to the extent that it should be considered when balancing a diet.
Bryan Miller has worked for companies which supply vitamins and minerals to pet food manufacturers. He has also developed formulations for several dog foods.