Diarrhoea can be caused by a number of things, but commonly in puppies (and kittens for that matter) it is often the result of having a heavy roundworm infestation. If your puppy only has loose bowel motions but is otherwise bright and well with no other symptoms then you should worm your puppy using a worm product recommended by your veterinary surgeon to ensure effective treatment.

Don't fall into the trap of thinking that it can't be a worm problem because you haven't seen worms passed - it can! If the diarrhoea persists for more than two to three days after doing this or if you see any blood being passed or if your puppy is sick, lethargic, losing weight or is unwell in any other way then you should take her to your veterinary surgeon for a check up immediately.