Blood in Diarrhea

Good morning. My 13 year old Chihuahua had bloody diarrhea last night. It was mostly mucus and darker red. He's acting completely normal and hasn't eaten anything that would cause an obstruction. He doesn't have any teeth and may have ate my larger dogs food, so wouldn't have been able to chew it. Could swallowing larger dogs food cause this?

Hello and thank-you for this interesting question.  The fact that the blood still looks like blood and not, say, black coffee grounds (after digestion), suggests that the blood is arising in the large intestine.   I am not sold on the suggestion that a large piece of kibble would cause bloody diarrhoea; working from my knowledge of anatomy, I'd have thought that even large kibble would be broken down to smaller pieces by the stomach acid - and that if it remained large but was scraping against the large intestinal walls late enough in the process to cause red blood (which signifies trauma in the wider large intestine), I would have expected some trouble swallowing and / or a large, hard / chunky, obviously painful faeces with problems passing it.  However feeding large kibble to a chihuahua with no teeth does sound very traumatic and is certainly best avoided.  It's worth putting this to your own vet and if they know something I don't please let me know. So what else might cause a dog to bleed into their large bowel? Other possibilities include certain parasites or viruses of the gut wall, but also problems with blood clotting.  Lumps or bumps - such as tumours, polyps or other inflammation of the large intestine - might also cause this effect.  Straining is not always seen with a lump because sometimes, until they reach a significant size, they simply 'bleb' out of the way when food passes. Most of these problems would be significant and therefore it is well worth asking your vet about; they will often recommend a small string of tests, starting with the most common or easy to rule out possibilities.