Mine tend to pick up something outside 3-4 times a year that causes them to have diarrhea... since antibiotics and running to the vets for this was getting old, she tried a different AB and put them all on probiotics for life, as they're better for them than taking ABs all the time. They haven't had diarrhea for about 3-4 years! Can you tell I love the stuff!
I use Nature's Farmacy brand (water soluble type)
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Yogurt doesn't have enough bacteria in it to do a dog a lot of good, to see quick results, best to use a product made for dogs or some use probiotics for people.