The primary function of pet food preservatives is to stabilize fats against oxidation. There are two types of antioxidants: natural and synthetic.

Natural antioxidants most often used are Vitamins E (tocopherols) and C (ascorbic acid).

  • There are eight different forms of Vitamin E, and they were not all created equal. The gamma and delta tocopherols are the best antioxidants in food. Alpha tocopherol is the form used to meet the pet’s actual Vitamin E requirement.
  • Vitamin C is most effective when combined with other antioxidants. Interestingly, Vitamin C salts (L-sodium or L-calcium ascorbate) and Vitamin C esters (ascorbyl-5,6-diacetate or ascorbyl-6-palmitate) are actually synthetic compounds that are perceived as acceptable “natural” preservatives.

Synthetic antioxidants are butylated hydoxytoluene (BHT), butylated hydroxyanisole (BHA), and ethoxyquin.

  • BHT and BHA have been used in human foods since 1954 and are most effective when combined. They have a maximum allowable concentration in pet foods of 200 parts per million (ppm). Detrimental effects have been noted when higher levels of BHT and BHA were consumed for an extended period of time.
  • Ethoxyquin is a synthetic preservative that has been approved in pet foods in the USA for more than 30 years with a maximum allowable concentration of 150 ppm. Ethoxyquin is considered the most effective antioxidant because it withstands the heat, pressure, and moisture of food processing that destroys natural antioxidants.

Commercially, ethoxyquin is the antioxidant of choice due to the compound's stability in processing, efficiency, and apparent low toxicity, and there is no evidence of detrimental effects when consumed at very high levels over a long period of time. It is a relatively expensive ingredient, so no more than necessary is actually used in pet foods.

Comparatively, tocopherols (Vitamin E) have a limited degree of effectiveness relative to the synthetic antioxidants such as BHA & BHT. These synthetic antioxidants have been shown to be three times more effective than tocopherols in preventing oxidation. Ethoxyquin has been shown to be five times more effective than the tocopherols; therefore, lower concentrations of synthetic preservatives are used in pet foods relative to the amount needed when using tocopherols or other natural antioxidants.

The FDA CVM has a legal maximum concentration of ethoxyquin at 150 ppm. However, most pet food manufacturers use less than 75 ppm in both dog and cat foods.

Ethoxyquin has received much negative press from pet owners and breeders. However, reports relating ethoxyquin to a wide spectrum of illnesses in dogs have not been supported by scientific evidence. The manufacturer of ethoxyquin has submitted the data from a large, long-term, multi-generational study to the FDA on the effect of feeding high levels of ethoxyquin to dogs. None of the dogs demonstrated any clinical signs of illness.