In recent years, pet owners have become increasingly aware of the use of preservatives in their pet's food. For the most part "preservatives" refer to the use of antioxidants and their use is essential in the production of dry pet foods. Without them oxygen would react with fats, oils, fat-soluble micronutrients and pigments resulting in rapid deterioration of the food through a process known as peroxidation or auto-oxidation, resulting in off flavours, texture changes, malodours, colour and nutrient loss, as well as harmful byproducts.

The success of antioxidants will vary both with their type as well as the stage of manufacturing at which they are added. Generally, the earlier in the production process the antioxidant is utilized, the more effective it is in enhancing shelf life.

Antioxidants can be categorized as synthetic or natural. The most common synthetic antioxidants are ethoxyquin, as well as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). These are preferred by pet food manufacturers due to their high effectiveness and low cost. For example, 150 PPM of ethoxyquin is equivalent to 1000 PPM of mixed tocopherols (Vitamin E).

With the high usage of the Internet by pet owners as a source of information (and misinformation), pet food manufacturers are under increasing pressure to avoid the use of synthetic antioxidants in favour of natural sources. The recent completion of a five year study to investigate any negative effects of ethoxyquin led the AAFCO (American Association of Feed Control Officials) to lower its requirement to 75 PPM from 150 PPM. Although this study found no harmful effects, consumer pressure has resulted in the use and marketing of natural antioxidants rapidly becoming the industry standard.

Plants, including herbs and spices, have provided a large range of compounds including Vitamin C, citric acid and a number of plant phenolic and carotenoids which control the oxidative processes. Of the naturally occurring antioxidants, Vitamin E is the most common. There are actually eight different forms of Vitamin E, but they are usually mixed and act together. Citric acid also assists in stabilizing and regenerating the antioxidant effects of the tocopherols. Additionally, compounds have been isolated from a number of herbs and spices that have shown commercially viable antioxidant activity. Sage, thyme and rosemary are some examples, with rosemary extract containing eight different phenolic compounds, which, like the tocopherols, also act together.

The difficulty with many of the natural antioxidants, particularly with the tocopherols, is not only their relatively high cost, but their own greater susceptibility to be broken down and weaker antioxidant activity when compared to synthetic antioxidants. This latter characteristic would shorten the shelf life of a dry food. Manufacturers attempt to manage this problem by using a complex variety of different antioxidants which have different properties, act together with one another and are effective in limiting the auto-oxidation process.

The practical consequence of the trend to natural antioxidant systems is a significantly diminished shelf life for the pet food. This impact has been less significant with small animal veterinary diets, as they tend to be lower in fats with lower levels of unsaturated fatty acids than commercially available dry pet foods. Nevertheless, it behooves consumers to store dry pet foods carefully, to control inventory levels, practice stock rotation and to adhere closely to the "best before" dates on packaging materials.