Quick answer: A probiotic label should be read together with its expiration or best-by date and storage instructions. The CFU number tells you about viable microorganisms, but the useful question is whether that amount is intended or guaranteed to remain available through the product’s shelf life—not merely what was present when it was manufactured.
What does CFU mean?
CFU stands for colony-forming units. It is a way of estimating viable microorganisms capable of growing under the test conditions used. A larger number can look impressive, but it is only one part of a probiotic label.
Why time and storage matter
Probiotic microorganisms can lose viability over time. Packaging, moisture, heat, formulation and storage conditions can affect how many viable organisms remain. That is why expiration information and storage directions belong in the same comparison as the CFU number.
CFU at manufacture versus through expiration
Some labels or marketing materials emphasize the amount present when a product was manufactured. That is not the same as telling buyers what level is expected later in the product’s life. When possible, look for language that connects viability to the expiration or shelf-life period.
What does research on expired probiotics show?
A published study of expired probiotic products found that some still contained viable organisms after expiration, but counts were generally lower than the amounts intended for use. That supports a practical conclusion: an expired product should not be assumed to deliver the same quantity shown for its intended shelf life.
Five label questions to ask
- What CFU or viability amount is stated?
- Is that amount connected to manufacture or expiration?
- Which organisms or strains are identified?
- What storage conditions are required?
- Where is the expiration or best-by date?
Is the highest CFU product automatically the best?
No. Strain identity, formulation, stability, evidence, serving directions and storage matter alongside CFU. Read our Dog Probiotic CFU guide for the broader comparison.
What should you do with an expired product?
Follow the manufacturer’s current guidance and replace a product when appropriate rather than assuming an expired probiotic still provides the labeled amount. Do not use appearance or smell alone to estimate viable microorganism counts.
Related PetVibess resources
- How to Store Dog Probiotic Chews
- Do Dog Probiotics Need to Be Refrigerated?
- Probiotic Strains for Dogs
- Dog Probiotic Buying Checklist
Sources
- MicrobiologyOpen: Expired Probiotics—What Is Really in Your Cabinet?
- Cornell University College of Veterinary Medicine: The Power of Probiotics
Written by the PetVibess Editorial Team. General educational and shopping information only. Updated September 19, 2026.