Most pet food labels include a few words and numbers that are easy to skip: an ingredient near the end of the list such as "mixed tocopherols," a best-by date stamped on the bag and a string of letters and numbers called a lot code. These details tell you how a food is protected from spoiling and how long it is expected to stay at its best. This guide explains how to read them on kibble, canned food, treats and fresh dog food. It is general information; for questions about your dog's diet, ask your vet.
Why dog foods need preservation
Foods spoil in two main ways. Fats and oils can oxidize and go rancid, which affects taste and smell and can reduce the quality of some nutrients. Microbes such as bacteria and molds can grow, especially in moist foods. Different types of pet food use different strategies:
- Dry kibble is low in moisture, which limits microbial growth, but its fats still need protection from oxidation. Preservatives and packaging help.
- Canned food is sealed and heat-treated so it is shelf stable until opened.
- Fresh and refrigerated foods rely mostly on cold storage, freezing and short shelf lives rather than chemical preservatives.
- Treats and chews vary widely depending on moisture and processing.
Natural preservatives
Many foods use preservatives derived from natural sources. Common names on ingredient lists include:
- Mixed tocopherols, forms of vitamin E used to slow fat oxidation
- Rosemary extract, an herb extract with antioxidant properties
- Citric acid and ascorbic acid (vitamin C), often used alongside tocopherols
Tocopherols used as preservatives do not necessarily count toward the vitamin E the food provides, so they are listed separately from added vitamins. Natural preservatives generally give a shorter shelf life than some synthetic options, so storage and dates matter more.
Synthetic preservatives
Some foods use synthetic antioxidants such as BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) and ethoxyquin. In the United States, these are allowed in animal feed within limits set by regulators, and the FDA's Center for Veterinary Medicine has reviewed their use over the years. Some owners prefer to avoid them, and many brands now advertise foods preserved naturally. If you have questions about a particular preservative, ask the manufacturer what they use and why, and talk to your vet about your dog's situation.
Note that a preservative may also be added to an ingredient before it reaches the pet food maker, such as fish meal or animal fat. Ask the company whether its ingredients arrive preserved and with what.
What "preservative-free" usually means
Labels such as "no artificial preservatives" and "preservative-free" are marketing claims, and they do not all mean the same thing. "No artificial preservatives" usually means natural preservatives are used instead. A truly preservative-free product typically relies on refrigeration, freezing, canning or very short shelf lives. Read the ingredient list rather than relying on front-of-pack claims alone. Our guide to dog food label names and marketing terms explains other common claims.
How fresh dog food is preserved
Fresh dog foods are usually shipped frozen or refrigerated, with little or no chemical preservation. That makes handling and storage especially important:
- Keep packs frozen until you plan to thaw them, following the maker's instructions.
- Thaw in the refrigerator, not on the counter; see thawing fresh dog food safely.
- Use thawed food within the time the label gives, often a few days.
- Discard food that smells off, looks unusual or arrived warm; see when a fresh food delivery arrives warm.
See how to store, thaw and serve fresh dog food safely for a full routine.
Best-by, use-by and other dates
Most pet foods carry a date, but wording varies:
- Best by or best before usually refers to quality. The food should keep its intended taste, smell and nutritional value until then if stored as directed.
- Use by is often used on perishable foods and is a firmer deadline.
- Production or manufacture dates tell you when the food was made, sometimes encoded within the lot code.
Dates assume proper storage. A bag left open in a hot garage, or a fresh pack left on the counter, may not last as long as the date suggests. Choose packages with plenty of time left before the date, especially if you buy large bags.
Lot codes and recalls
The lot code identifies the batch a product came from. If a recall happens, companies and the FDA list affected lot codes and dates, so it pays to keep that information. Take a photo of the label or keep the bag until it is finished. Our guide to checking dog food recalls and lot codes explains how to check.
Storage after opening
Once opened, foods start to change:
- Kibble: keep it in the original bag, rolled closed, inside an airtight container, in a cool, dry place. The bag helps protect food from light and air and keeps the lot code and date handy.
- Canned food: cover and refrigerate leftovers, and use them within the time the label recommends.
- Treats: reseal packages and watch for mold, especially in soft, moist treats; see reading dog treat and chew labels.
Signs a food may have gone off
Dates are a guide, not a guarantee. Before serving, use your senses. Kibble that smells sharp, sour or like old cooking oil may be rancid. Look for mold, clumping from moisture, insects or packaging that is torn, swollen or damp. Canned food in a bulging, leaking or badly dented can should be discarded unopened. Fresh food that smells unusual, looks slimy or has changed color should go in the trash. If your dog suddenly refuses a food they usually love, check the package before assuming they are just picky, and contact your vet if your dog becomes unwell after eating.
Questions to ask manufacturers
If labels do not answer your questions, contact the company. Useful questions include which preservatives the food and its ingredients contain, how long the shelf life is from production, how the date code works and what storage conditions they recommend after opening. Reputable companies should be able to explain.
Bottom line
Preservatives protect fats from going rancid and keep foods safe for their shelf life, and fresh foods rely mostly on cold storage instead. Read the ingredient list rather than front-of-pack claims, note best-by dates and lot codes, store food as directed and contact the maker if you want to know more about how a food is preserved.
About this guide
Our guides explain how to read labels, plans and specs so you can make your own choice with your vet. We don’t make health claims, we haven’t hands-on tested products, and we don’t publish invented statistics or ratings. Product facts come from official brand pages. How we work.
Product images are illustrative stock photos, not the exact products listed, except Petcube cameras, which show Petcube’s own product photos. Photo credits