Probiotics for dogs and cats. Why CFU cannot be compared with milligrams

Probiotics are the one category where our usual arithmetic does not work. Every other ingredient on this site can be expressed in milligrams per kilogram of body weight and compared on that basis. Probiotics cannot, and that is inherent rather than an oversight.

CFU instead of milligrams

A probiotic delivers living microorganisms. They are measured in colony-forming units, or CFU, meaning the number of organisms capable of multiplying. The weight of the powder says nothing about that: a gram of carrier with few organisms weighs the same as a gram with very many.

The amount we measure against is on the probiotics ingredient page. It is stated there as a fixed daily amount per animal rather than per kilogram, because the trials gave every animal the same amount whatever it weighed. That is what sets this ingredient apart from every other one here, and it is not sloppiness: a count of organisms acts in the gut, not in proportion to body mass.

What counts as a sensible amount also depends on the strain, and one strain is not interchangeable with another, not even within the same species.

The strain is the real declaration

A usable pack names not "lactic acid bacteria" but the genus, species and strain designation, for example Enterococcus faecium NCIMB 10415. Only the strain designation makes it possible to trace what any claim refers to. In feed, only certain strains are approved as additives, and the approval number is then printed on the pack as well.

Equally important: the CFU count at the end of shelf life, not at manufacture. Living organisms die off during storage. A figure "at manufacture" describes a state you are not buying.

Prebiotics are something else

Prebiotics such as FOS, MOS or inulin are not organisms but fibres that serve as substrate for the bacteria already present. They are dosed in milligrams, and we found no sound reference amount for them: we show what is on the pack but do not rate it. Many products combine the two. That is reasonable, but it makes comparison harder, because two different units then sit side by side on the pack.

What this means for comparisons here

In the finder, probiotics therefore do not appear in a per-kilogram calculation. We show the CFU figure, the strain designation and the cost per day, and we compare them only with other probiotics. Setting a product with 2 billion CFU against a joint powder with 500 mg of mussel would produce a number with no meaning.

Expectations

Digestion is varied. A change of food, a worm burden, swallowed grass or stress all produce similar pictures and have nothing to do with each other. Supplements are not a medicine. If stools stay changed over several days, if vomiting is added, or if your animal eats less, that should be looked at before you supplement anything.