Diarrhea in Dogs

Diarrhea is one of the most common reasons dogs visit the veterinarian. By definition, diarrhea means repeatedly soft or loose stool due to excess fluid. One episode of loose stool is usually not an emergency, unless it is paired with other concerning symptoms.

There are two main types of diarrhea. Large bowel diarrhea happens when the colon does not properly reabsorb fluid. Small bowel diarrhea occurs when the small intestine sends poorly processed ingesta to the colon, which cannot form normal stool. Both types can be caused by many factors—some originating in the digestive tract, others as a side effect of disease elsewhere in the body. Common examples include parasites, liver or kidney problems, or simply eating something that doesn’t agree with your dog’s system.

What to Watch For

• If your dog develops diarrhea, monitoring certain details can help both you and your veterinarian:

  • Recent changes: Has your dog had new food, treats, supplements, medications, or stress in the past 72 hours?

  • Blood: Is there bright red blood (frank blood) or black, tarry stool (melena)?

  • Frequency: How often are episodes happening? Remember, count episodes, not piles. If your dog squats multiple times during one outing, that’s still one episode.

  • Stool volume: Is the total daily amount similar to normal, or increased?

  • Urgency & straining: Does your dog urgently need to go or seem to struggle to pass stool?

  • Classification: Knowing fecal score for different episodes can help communicate with your veterinarian (chart below)

Diarrhea vs. Constipation

Sometimes diarrhea looks like constipation, especially in unsupervised outdoor dogs. A constipated dog strains but produces little to no stool, while a dog with profuse diarrhea may strain repeatedly due to urgency. As a rule of thumb: dogs with diarrhea usually pass stool within a couple of hours. If your dog strains unproductively for more than six hours, constipation is more likely. If no stool passes within a full day, veterinary care is recommended.