FOOD CHOICES
Commercial dog foods come in a variety of forms. The most common types are dry, semimoist, and canned. The moisture content of these foods ranges from 6 to 10 % for dry, 15 to 30% for semimoist, and 75% for canned. Most canned food has relatively more fat and protein and fewer carbohydrates than does dry and semi-moist food, and generally contains much higher levels of animal products.
Pet food labels must list the percentage of protein, fat, fiber, and water in the food. When reading labels, it is important to remember that what may appear to be a big difference in the amount of a nutrient—for example, 8% protein in a canned dog food vs. 27% protein in a dry dog food—reflects the fact that there is more water in the canned food.

PET FOOD ADDITIVES
Some other substances that might be found in pet foods, which are not required nutrients, are described below:
Chondroprotective agents are used by the body to make cartilage and joint tissues.  Although, use of chondroprotective agents may be indicated for selected clinical conditions, widespread inclusion in the diets of healthy populations may not be warranted at this time.
Antioxidants work to prevent oxidative damage to nutrients and other compounds in the body and inhibit or quench the formation of free radicals. At this time, data are lacking to make specific recommendations beyond those for the essential vitamins and minerals that are components of antioxidants.

Herbs and botanicals are used in pet foods either to provide flavor or, more often, to have a medicinal  effect on the body. This is especially true in the case of extracts, where the classical nutritive components of the plant may be separated from the extract in the process.  Because the intended functions are more pharmacologic versus nutritional in nature, discussion of potential benefit is beyond the scope of this publication.
Flavors and extracts derived from animal tissues such as poultry or fish are considered “natural” flavors.  A wide variety of flavors can be derived from other animal and plant materials, including dairy products, eggs, herbs, and spices.  Acceptable processing methods include roasting, extraction, and fermentation. Except for artificial smoke and bacon flavors, synthetic substances are rarely used in most dog foods.
Colors are synthetic compounds used to replace or accentuate the inherent color of the food.  Only certified colors approved for use in human foods are allowed in pet foods.  Iron oxide is a synthetic but noncertified color that can be used at levels not to exceed 0.25% of the pet food product to give dog t food a red, meaty appearance. Titanium dioxide is another common color additive in human and pet foods because it can induce a “brightness” in foods by complementing other color additives.  Its use is limited to 1% of the food by weight.

This information is based on recommendations from the 2006 release of Nutrient Requirements of Dogs and Cats. The report contains useful information for companion animal nutritionists, veterinarians, scientists in industry and academe, regulators, pet owners and anyone with an interest in the health and welfare of these important animals. To order the report, contact the National Academies Press, 500 Fifth Street NW, Washington, DC 20001; (800) 624-6242 or http://www.nap.edu.