Liz Buchanan BVSc MRCVS
Keymaster
Hello!  There are many different causes of diarrhoea. Some will get better by themselves and some will gradually get worse, or at least continue to drain fluid from the body until it is struggling. From here, it's very difficult to tell one type from another. Switching food suddenly can certainly cause or exacerbate it, so where a bland diet seems to have brought about resolution, it's always best to make the switch back to normal food very slowly. For example, by feeding a small amount of normal food mixed with the bland food at first, and if that causes no problems then increasing the proportion of normal food slowly, bit by bit. Causes can include dietary insensitivities, bacterial disease (hand washing vitally important), allergies, Giardia, Parvo, even pancreatitis or liver disease and the cuase - and patient health - dictate the outcome. Diarrhoea gets particularly dangerous when too much fluid has been lost from the body and cannot be replaced through drinking; at this point, a drip is often needed. Therefore, at some point your vet will want to check your dog in order to make sure that their vitals are ok and that there is no more they need to do for him. They may be happy to triage (work out the level of urgency) over the phone in order to decide how soon they need to see you, but it is important to give them the chance to intervene if they need to. Best of luck and please do let us know how you get on.
Report