Dear Doctor – Expired Pet Food

Letter to Tufts Veterinarians


Expiration dates on pet food
Q I recently bought several large bags of a high-quality cat food on sale at our local pet store. Unfortunately, I just realized that the “best by” date has been passed by a couple of months on two of the bags (the third bag’s date is okay).

Should I now consider this food to be unhealthy for my cats and throw it away? Any advice would be greatly appreciated.
Donald R. Olson

A Dear Donald: Reputable pet food manufacturers set their product expiration dates to ensure that all nutrients are at adequate concentrations throughout the shelf life of the product, based on testing and knowledge of degradation rates of various nutrients with storage.

While pet food with a “best by” date of yesterday is unlikely to cause health problems, it is hard to know at what point after that date the food will no longer meet essential nutrient needs — is it days, weeks, months? The answer will depend on the composition of the food and the packaging, as well as how it was stored before and after purchase. The safest bet is to replace food that is past its “best by” or expiration date.

A related concern is how long food should be kept once the package has been open. Again, this is likely dependent on nutrient composition and storage conditions, but a good rule of thumb for dry food is to buy bag sizes that you can use up in about one month. Opened cans should be covered and refrigerated and kept no longer than three to seven days. While buying large bags may seem cost effective, the risk of nutrient degradation is increased if it takes a long time to finish an open bag. Alternatively, the food manufacturer can be contacted for storage information specific to their diets.

It is best to always store food in the original packaging, tightly closed. However, if you do need to take it out of the package for any reason, be sure to save the portion of the bag or label that includes the lot number, expiration date, and manufacturer contact information, just in case.
Cailin Heinze, VMD, MS, DACVN
Assistant Professor of Nutrition
Cummings School of Veterinary Medicine
at Tufts University


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