I did some reading of the peer-reviewed literature, and the probiotics business is pretty much the Wild Wild West, let the buyer beware. Here is a link to an article where 19 commercial dog and cat foods claiming to contain probiotics were analyzed in the lab for bacterial count and species composition:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC340078/ . Summary: They either didn't carry any bacteria at all, carried much less than claimed on the label, or carried different bacteria from those listed.
There may be good products out there, but I'd double check with a vet or a vet nutritionist first for recommendations. I did see a liquid probiotic advertised that claims to be fairly flavorless and stable at room temperature:
https://www.maryruthorganics.com/pro...00-plant-based . You can read all of the package label on that website. It doesn't say how many bacteria the product contains, and has a statement that says, "These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease."