Antioxidants are substances that help to keep fats and fat-soluble ingredients (including vitamins A and E) from becoming oxidized. Once a fat is oxidized, it starts to taste rancid and loses much of its nutritional value. Dog and cat foods, which often contain significant levels of fat, are especially susceptible to oxidation. Canned foods are protected because they are airtight, but dry foods need to have antioxidants added to preserve them. If an antioxidant is used, the Association of American Feed Control Officials (AAFCO) guidelines require that the common name of the antioxidant must appear on the label, along with a reference to the fact that it is being used as a preservative.
There are both natural and artificial antioxidants, and they all work to preserve food from oxidation. The most common artificial antioxidants used in the pet food industry are ethoxyquin, butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA). Commonly used natural antioxidants include tocopherols (vitamin E), ascorbic acid (vitamin C), citric acid, and rosemary.
Artificial preservatives definitely keep ingredients stable longer and give a longer shelf life than natural antioxidants. However, consumers have had concerns over the safety of artificial preservatives in pet food. The most controversial of these has been ethoxyquin, which has been approved for use in animal feeds for over 30 years. It is currently allowed in dog foods at levels of up to 150 parts per million (ppm), or 0.015%.
About 10 years ago, the Food and Drug Administration (FDA) began receiving reports from dog owners who felt that ethoxyquin was related to the development of medical problems in their dogs, including allergic reactions, skin disease, organ failure, cancer, and behavior problems. There has been speculation that in the late 1980's, some companies that were making high performance foods began adding extra ethoxyquin as an inexpensive way to extend the shelf life of these higher-fat products. However, there are also those who maintain that most pet food manufacturers who were using ethoxyquin at that time, were actually using much lower amounts than that allowed by law. Without scientific evidence, it has been difficult to determine whether or not the problems reported were truly related to the use of ethoxyquin, and at what levels.
In 1997, the FDA reviewed a study done voluntarily by Monsanto, a major manufacturer of ethoxyquin. The results from this study showed that ethoxyquin levels above the current amounts allowed in dog foods produced no reproductive abnormalities. The only adverse effects noted were mild increases in the blood levels of certain liver enzymes and an increase in the levels of a normally-occurring red blood cell metabolite. These increases occurred in the livers of lactating bitches, who generally eat more than other dogs. These liver changes are considered to be mild and may resolve when the dogs return to eating less food; however, the complete health significance will not be known without further investigation.
The FDA felt that allowing ethoxyquin to be used at 150 ppm might not provide an adequate margin of safety in lactating females and possibly puppies. In July 1997, the FDA sent letters to the manufacturers of ethoxyquin and to the pet food industry, requesting that the maximum amount of ethoxyquin used in pet foods be voluntarily lowered from 150 ppm (0.015%) to 75 ppm (0.0075%). It appears that all pet food manufacturers have complied. There is a study being performed by the Pet Food Institute, an organization that represents pet food manufacturers in the United States. This study is designed to determine whether even lower amounts of ethoxyquin (30 or 60 ppm) would provide adequate antioxidant protection for dog food.
BHT and BHA are synthetic analogues of vitamin E, and are often used together. BHA is relatively stable at high temperatures. Both of these antioxidants are Generally Recognized as Safe (GRAS) by the FDA when used at specific levels, and they are the most common preservatives in human food. There is, however, continuing controversy as to the safety of these substances, as well. Both have been suspected of being carcinogens; however, in 2 animal studies, BHT and BHA have been shown to actually protect against cancer if they are added to food before an animal is exposed to a carcinogen. More research is needed to determine the true effect of these preservatives.
Some consumers prefer pet foods with only natural preservatives. Vitamin E, vitamin C, citric acid, and rosemary are among the most commonly used natural antioxidants. Mixed tocopherols are a common source of vitamin E in pet foods. Vitamin C is provided by ingredients such as cranberries, blueberries, apples, and some other fruits. Citric acid is also found in many of these, especially citrus fruits. Rosemary is an extract from the plant Rosmarinus officinalis, an evergreen shrub which has anti-oxidant properties.
If you choose to use a dog food containing natural preservatives, keep in mind that they cannot extend shelf life as long as the artificial preservatives can. Consider buying the food in smaller amounts, to make sure that it is used up before it loses its freshness or nutritional value. Look for foods with a 'best if used by' date stamped on them. Store these foods in a dry location, away from excessive heat or humidity. If possible, place the bag inside another clean, dry container once it has been opened.
To make wise decisions when selecting your dog's food, become an informed consumer. Learn all you can about the various ingredients in pet food, and why they are used. Beware of claims that can not be backed up with scientific evidence, or that seem to go against your common sense. Watch for new information and reports on nutrition from knowledgeable sources. Being informed about pet food is another way you can help to protect your animal's health, so that you can enjoy many happy years together.