Dog diarrhea
Loose stool has a wide range. One soft pile after a stolen sandwich is ordinary. Watery stool with blood in a puppy is not. Sort the dog in front of you before you change foods.
Describe the stool
Soft-serve stool that still has shape is milder than liquid that hits the floor. Mucus streaks suggest large-bowel irritation. Fresh red blood on top of stool is hematochezia. Black, tarry stool is melena and can mean bleeding farther up. Both blood patterns deserve a call the same day, and sooner if the dog is weak.
Straining a small amount of mucus can look like constipation when it is actually colitis. If you are unsure, take a photo. Frequency matters as much as texture: three accidents in an hour is a different problem from one soft stool in the yard.
Puppies and small dogs
Parvovirus still shows up as vomiting plus foul diarrhea, often with blood, in incompletely vaccinated puppies. They dehydrate fast. Do not wait a day to see if a quiet puppy "works it out." Bring vaccine records. Clinics will often want that dog isolated from the waiting room, so call from the car.
Toy breeds and puppies have less fluid to lose. Sticky gums, skin that stays tented, or a puppy who will not stand are emergency signs. Offer water unless the dog is vomiting the water straight back. Do not syringe-force large volumes.
Adult dogs you can watch briefly
A bright adult who has one or two soft stools, a normal appetite, and no blood can often be fed the usual diet in smaller meals for a day. Skip treats, rawhides, and table food. Many dogs improve when the trigger was a single dietary indiscretion. If the diarrhea is still going at the 24-hour mark, or the dog skips a meal, book a visit.
Chronic soft stool, weight loss, or diarrhea that returns every few weeks needs a workup. Parasites, food intolerance, pancreatic disease, and inflammatory bowel disease do not announce themselves clearly from the driveway. A fecal test is a reasonable first step and is not the whole answer when the dog is losing weight.
Medicines to skip
Do not give loperamide or human bismuth products unless a veterinarian has already told you that drug is acceptable for that dog. Collie-type breeds can be sensitive to some gut drugs. Antibiotics are not automatically useful for simple diarrhea, and leftover tablets from a previous illness are a bad idea.
The when-to-see-a-vet checker separates bleeding and collapse from a single soft stool. More dog symptoms are listed on the vet help hub.
Sources
Clinic decisions belong to the veterinarian who can examine the animal. This page is background reading.
Dog diarrhea questions
How long can dog diarrhea wait?
One mild episode in a bright adult can be watched for a day. Blood, black stool, vomiting, or a dull puppy should be seen the same day.
Is pumpkin enough?
A spoon of plain pumpkin is not a treatment for infection, parasites, or a foreign body. It does not replace an exam when the dog is sick.
What does black stool mean?
Tarry black stool can mean digested blood from higher in the gut. That deserves a prompt clinic visit, not a home diet trial.