A sleepless night with a puppy with diarrhea is enough to make one reconsider your acquisition. Diarrhea is a common problem, but there are many different causes.
Young dogs often have loose stool due to excitement, stress, dietary changes, and internal parasites. More serious causes seen in young dogs are blockages and viruses like distemper and parvovirus infections. Other causes seen at all ages include food intolerance, infections, inflammatory disorders, enzyme deficiencies, and cancer.
An acute bout of diarrhea can often be managed at home. Withholding food (NOT water) for 24 hours is often enough for the disorder to pass. If diarrhea is accompanied by severe lethargy or repeated vomiting, professional care should be sought promptly. Dehydration can be a life-threatening condition in a dog with increased output (diarrhea) and decreased intake (not drinking) or vomiting.
Sometimes diarrhea is noted to be associated with straining or mucous or blood. This usually indicates a disorder of the large intestine (colon) and is managed a little differently from disorders of the small intestine.
Sometimes the observation of diarrhea is actually due to constipation, as only fluid can bypass the hard obstruction. Conversely, when straining is present, constipation is not necessarily the cause. Spasms from a colon with diarrhea can make a pet appear to be constipated.
Fortunately, most cases of diarrhea will respond to treatment and result in a happy pet and a happy owner.