Many consumers have begun to question the presence of preservatives in dog food. Whether we like the idea or not, preservatives must be used in dry foods to combat the ill effects of exposure to oxygen. Preservatives are used in dog food primarily to stabilize fat. Since canning is itself a preserving process, additional preservatives do not have to be added to canned food.
The problem that preservatives address is the interaction of oxygen with fat known as oxidation which causes rancidity. Most fats used in dog food are pre-treated with antioxidants (compounds that prevent this reaction) before they are even shipped to the pet food manufacturer. Pet food makers generally tell their suppliers which antioxidants they will and will not accept. In the past, preservatives added by the supplier were not usually disclosed on the label, in defiance of an FDA regulation which required this. However, the majority of manufacturers now list the fat preservatives on the label, so you will usually see something like: Chicken fat (preserved with BHA).
Besides preventing rancidity, preservatives can also retard the growth of microbes like bacteria. While extruded foods are relatively sterile after departing from the high temperature and pressure environment of the screws, they may be re-contaminated during the drying process, or by bacteria lurking in the sprayed-on coating materials. Mold spores, which are ubiquitous in the air, can also sneak into the bag with the food. Preservatives also help prevent deterioration of vitamins (especially the fat-soluble vitamins A, D, E and K), energy value, and amino acid availability of the food.
There are several synthetic antioxidants that are commonly used in dry dog food. Propylene glycol, the main ingredient in the new safer antifreeze, is a close relative of the highly toxic ethylene glycol. It is banned for use in cat foods because it damages feline red blood cells. No evidence has been found, however, that this occurs in dogs. It is mainly used in soft-moist foods, such as the squishy bits and chunks found in some dog foods.
Ethoxyquin, made by Monsanto, is a very effective antioxidant, but it has come under fire for suspected harmful effects. The pet food industry contends that no one has ever proven that Ethoxyquin is unsafe, but consumers complained of numerous health problems in dogs who ate foods preserved with the product. Today, Ethoxyquin is rarely seen in over-the-counter dog foods, although some makers still use it in their veterinary prescription-type diets.
Butylated hydroxyanisole (BHA) and Butylated hydroxytoluene (BHT) are very popular preservatives in the pet food industry and the human food industry. They are chemically similar, but BHT is more toxic to the kidneys than BHA, according to researchers at Michigan State University. BHT is prohibited as a food additive in England.
All of these chemicals are quite effective preservatives, providing a stable shelf life of at least 12 to 16 months under ideal storage conditions.
Interestingly, synthetic antioxidants have been shown in studies to have a protective effect against certain liver toxins and some tumors in animals, although some appear to actually promote other cancers, such as stomach, kidney, and bladder cancers. Ethoxyquin, BHA and BHT are well known to cause hypersensitivity (contact allergies) in chemical industry workers whose skin is chronically exposed to these chemicals. There is some evidence that Ethoxyquin may contribute to chronic kidney disease.
Because fats, oils, and other ingredients may be treated with antioxidants before they get to the pet food manufacturer, even canned foods (which dont need preserving due to the oxygen-free environment in the can) are likely to contain them. One industry supplier claims that it is very difficult to buy stable animal fat, poultry by-products, meat meal and fish meal without Ethoxyquin. In fact, fish meal, which is a very common ingredient because of its rich flavor and nutrient value, is heavily preserved because of its unfortunate tendency to auto-combust in warm temperatures. (Several cargo ships carrying unpreserved fish meal have even experienced fires or explosions due to the heat generated by oxidation reactions!)
Federal and state regulations restrict the levels of the artificial antioxidants in animal feed, including pet food, generally to 0.15 to 0.02 percent of the fat content. A total Ethoxyquin level of 150 ppm is permitted in animal feed, fish food, and pet food by law. In 1997, the FDA requested that pet food manufacturers voluntarily limit ethoxquin to 75 ppm based on new data from Monsanto. However, the only manufacturer still using Ethoxyquin in its over-the-counter foods recently stated that Ethoxyquin levels in its foods do not exceed 200 ppm, well over FDAs suggested limit. Oddly enough, Ethoxyquin is allowed by federal regulations only in canned pet food not dry. However, the pet food industry has amply demonstrated its propensity for disregarding such inconvenient laws, and FDA lacks the manpower and resources to enforce them.
By way of comparison, Ethoxyquin in forage crops for food-producing animals is limited to 5 ppm. In human food, ethoxyquin is restricted to 100 ppm as a color preservative in chili powder, paprika and ground chili not exactly high-consumption items! and maximums of 0.5 ppm in eggs, zero in milk. BHA and BHT, however, are widely used in foods for human consumption.
Many pet food makers are now using so-called natural preservatives: ascorbic acid (vitamin C) and mixed tocopherols (vitamin E); and some even use such exotic items as rosemary extract. (Actually, what we consider vitamin E, alpha-tocopherol, is not an antioxidant itself, but the rest of the tocopherol complex, about seven compounds in all, do have that action).
Natural preservatives may not provide as long a shelf life they are said to be most effective for seven to nine months, though some companies have managed to stretch this to 12 months by combining several natural preservatives. Even if they are somewhat less reliable, natural preservatives are at least not harmful to our dogs, and may even provide a few extra vitamins.
How long can this last?
So, now we have a finished dry dog food in the bag, complete with preservatives what happens next? If there is a limited shelf life, dont we want to make sure that the food we buy is safely within those limits?
There is no legal requirement for manufactured on, expiration or best used by dates on pet food packaging, nor is there even an accepted industry-wide standard. A few years ago, most dog food labels were coded in a way that very deliberately obscured the actual date of manufacture. Fortunately for us, this has shifted toward providing more consumer-friendly information.
After a period of confusion where various labeling schemes were used, the largest companies have set a sort of de facto standard: rather than stamp the manufacturing date on the package, they use a best used by date. This date is usually 12 to 16 months after the date of manufacture. But it is still impossible to tell from the label exactly when the food was made or what the shelf life should be.
Lamentably, some companies dont use a date stamp at all, and a few still use coded stamps that prevent you, the consumer, from knowing anything about when the food was made at all, or how long it is supposed to last. It is probably best to avoid such foods, if for no other reason that to reward the manufacturers who do provide such information for being honest and above-board.
The manufacturers agree that, when its present, the best used by date is just that do not buy a food that is nearly at its date, if you plan to be feeding it for several weeks. The period of time the bag is at your house and being fed, right down to the last kibble, must be included in the shelf life.
It is extremely important to check every bag you buy for a date stamp. In my research, I found several lots of food that had best used by dates that were long since passed. They were still sitting on store shelves months after they should have been discarded! The manufacturers rely on the stores to rotate their stocks, but even at the big pet food retailers, this does not always happen.
It is preferable to buy food that is closer to its manufacture date than a food that has been sitting in a warehouse or on a shelf for 10 or 11 months. No matter what preservatives are used, there will always be some deterioration of the food over time. The nutritional value will be compromised, and the food may even become unpalatable to the dog. I recommend buying only the freshest foods and using them as soon as possible especially the naturally preserved foods.
Finally, it is important to remember that, no matter what preservatives are used or what the expiration date is, any dog food will deteriorate rapidly if exposed to adverse conditions, such as widely varying temperatures, excessive heat, or moisture.
-By Jean Hofve, DVM
Dr. Jean Hofve is the Companion Animal Program Coordinator for the Animal Protection Institute, located in Sacramento, California.