What Causes Yellow Stool in Dogs?

When a dog’s stool is yellow, this indicates that there is an irritation in his digestive system or an infection. The yellow colored stuff is mucus, which acts as a lubricant to help move the stool through the intestinal tract and out of the dog’s body. Yellow mucus is not typical. The more irritated the dog’s system the greater amount of yellow mucus that will be produced.

...
Yellow stool can be an indication of several different medical problems.

Other Possibilities

A dog’s system can produce yellow mucus in the stool because of a food allergy, or it can also be an indicator that the dog has an intestinal blockage.

Giardiasis

When a dog has an infection called giardiasis, which is an intestinal infection caused b y a parasitic protozoan, this can cause his stool to turn yellow. However, the stool of an infected dog is normally pale, greasy and terribly stinky. A dog becomes infected when he eats the cyst form of the parasite. The cyst then opens up in his intestine and releases trophozoite, which is an active form of the parasite. They attach to the wall of the intestine and then divide and are passed into the dog’s feces.

Diarrhea

When a dog has diarrhea, the stool can turn yellow. Yellow stool means that the stool is traveling very quickly through the small intestine. When a dog has diarrhea and it’s yellow, it can also mean that he is eating foods that he can’t tolerate; so the dog's food should be changed. Yellow diarrhea can also be caused by medications to treat parvo virus as well as pancreatic enzyme replacement pills.

Young and Old

If your dog is a puppy and is eliminating yellow poop, you need to take it to the vet. If a puppy drinks too much milk, this can turn his stool yellow. Puppies can easily be killed by an infection, so treatment must begin ASAP. If your dog is elderly and has yellow mucus in his stool, this needs to be addressed. Old dogs have difficulty fighting off parasitic infections or other illnesses.