Your dog’s poop will become black and tarry because of the presence of digested blood.
How does digested blood end up in the poop? When your dog is bleeding in the stomach or small intestine, iron in the blood oxygenates as it moves through the colon, which is what gives it the black color. It might not look as scary as fresh, bright red blood, but it reflects a serious problem.
When blood doesn’t look like blood
Blood isn’t always the bright red color we expect to see. In the poop, blood looks like blood only when the bleeding is in the large intestine or rectum.
When the bleeding happens higher up in the digestive tract, or blood from the mouth or respiratory tract is swallowed, the digestive processes change what it looks like.
It is still blood.
While finding a bit of fresh blood in the feces may or may not represent an emergency, I’d always consider black, tarry stool to be one unless proven otherwise. It can, sometimes, have a benign reason behind it, but how would one know?
Why is digested blood in the feces scarier then fresh one?
A speck of red blood can quickly get your attention. It takes a substantial amount of blood to change the appearance of the stool to look black and tarry. So you’re not looking at a few drops. Which means a substantial bleed.
That’s why black, tarry stool would scare me way more than a bloody one.
You might be looking at a severe, life-threatening illness. The potential causes of tarry stools in dogs include:
- bleeding ulcer
- tumors in the stomach or esophagus
- severe infection
- damage from a foreign body
- abnormal blood clotting
- kidney failure …
Other symptoms that ought to provide a clue about the seriousness of your dog’s situation depend on where the blood is coming from and can include:
- vomiting (with or without blood in it)
- pale gums
- difficulty breathing
- coughing up blood
- bleeding elsewhere
- and so on
If my dog passed black, tarry stool, I am on my way to a vet.
My Dog’s Poop: What Can You Learn from Your Dog’s Stool