Blood bright red is "fresh blood" (hematochezia) coming most likely from the lower intestines, as the colon , or rectum.
The blood in the stools causes feces to appear as black and tarry most likely is the digested blood and coming from the upper intestinal tract. (Melena)
There is a variety of causes, why you find blood in your dogs stool. The range can be from minor causes,such as dietary changes to severe cases, as parvo, and cancer.
Causes of Hematochezia (light red blood):
- Parasites (usually the most common cause)
- Dietary changes (dogs must be switched to new foods gradually)
- Rectal injuries (your dog ate sticks, rocks, bones, Avoid giving cooked bones and sticks to play with. Also check the rectal area for any rectal injuries especially involving the anal glands.)
- HGE (Hemorrhagic gastro-enteritis )
Causes of Melena
- Blood ingestion (when your dog licked a bloody wound of his for instance, or had a bleeding mouth injury)
- Aspirin (If your dog is on aspirin , he may develop ulcers from its use. A bleeding ulcer will typically have black, tarry stools meaning digested blood coming from the stomach. Inform your vet promptly and if your dog is on such medication, keep a watchful eye on the stools.)
Always consult your veterinarian.The article above is only for your awareness about your dogs stool and general health issues