Green feces in dogs are caused by intestinal disorders and parasite infections, according to VetInfo. The ingestion of grass can also cause a dog's feces to be green.
When the green color is caused by intestinal disorders or parasite infections, such as roundworms, the stool appears slimy, according to VetInfo. Roundworms are parasites that attach themselves to the intestinal lining and multiply and cause great discomfort for the dog. A fecal examination by a veterinarian can determine the underlying cause of a dog's illness. Observations of the dog can help the veterinarian make a diagnosis. Symptoms of constipation, diarrhea or straining to defecate also help the vet to make the correct diagnosis.