If you’ve looked at a dog supplement containing probiotics, you’ve likely seen the term “CFU” listed next to a large number. But what does it actually mean — and why should it influence your buying decision?

CFU stands for colony-forming units. It’s a measurement of the number of live, viable bacteria present in a single dose of a probiotic product. Essentially, it tells you how much active bacterial content your dog is actually receiving — not just whether probiotics are present in the ingredient list.

This number matters because probiotics work through colonization. For beneficial bacteria to have a meaningful effect on the gut microbiome, enough live organisms need to survive the journey through the digestive system and establish themselves in sufficient numbers. A product with too few CFUs may simply not deliver enough bacteria to make a measurable difference.

Equally important is strain specificity. Not all probiotic bacteria behave the same way. Different strains offer different benefits — some support gut lining integrity, others aid nutrient absorption, and others assist with immune regulation. This is why effective probiotic blends, like those found in TrueHealthPet Digest and Vitality, list specific strains: Lacticaseibacillus casei, Limosilactobacillus fermentum, Limosilactobacillus reuteri, Pediococcus acidilactici, and Levilactobacillus brevis.

TrueHealthPet Digest contains 250 million CFUs per soft-chew, while Vitality includes 125 million CFUs — dosage differences that reflect each formula’s specific purpose. Digest is built around comprehensive gut health support, while Vitality incorporates probiotics as part of a broader immune and joint-focused formula.

When evaluating any probiotic supplement for your dog, look past the word “probiotic” itself. Check for a specific CFU count and named bacterial strains. This level of transparency is a strong indicator of a product formulated for genuine results, rather than one using probiotics as a marketing buzzword.