Probiotics can be given to dogs on a long-term basis, but the specific duration will depend on the reason for giving them. If your dog is taking probiotics for a specific digestive issue, you should follow your veterinarian’s recommendations for how long to give them. In general, probiotics are given for a minimum of several weeks to allow enough time for the beneficial bacteria to colonize in the gut and produce a positive effect.
If your dog is taking probiotics for general gut health maintenance, it is generally safe to give them on a long-term basis.