My dogs, a havanese and a mixed breed, have both had diarrhea on and off for a month. They eat different food and they have been on the same food for years, so it's not that. The vet gave medicine which helped, but the minute they got back on regular food, it started again. If I give them boiled chicken and rice they are ok. I don't think the gardener has put down any chemicals. The only common thread I can think of is that we brought home unwrapped bully sticks from a shop we visited on vacation a month ago. Can Bully sticks transmit bacteria that might cause this?