I used to use yogurt, didn't have the kind of luck with it that I really wanted. I had a guinea that was on antibiotics (various ones) for months and months (and months). We were really lucky that he only had diarhea problems occationally. But what we found worked like magic for us. The vet gave us a prescription product called Beneback (or Bene-bac). What this turns out to be is concentrated gut bacteria in a tube. It cleared up piggies diahrea over night the first time! It probably gave my pig another several months of life. They have sure come a long way since I started with my guinea pigs, what with "critical care for herbivors" food and beneback. (When I first started with pigs, the vet I knew used to have to call around to labs and vet schools to get answers because he said the information on pet cavies just isn't out there. Thank goodness that is changing).