Usually, you need not worry about seeing a small amount of mucus in your pet's stool. Dog stool normally contains some mucus -- a slime-like substance made by the intestines to keep the lining of the colon lubricated and moist.
But if you notice an excessive amount of mucus in the stool, or if it is accompanied with blood or a radical change in your dog's bowel movements, seek immediate veterinary medical attention. He or she will be better able to identify the underlying cause and recommend a proper course of treatment. Common causes include:
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The very end of the large intestine
A type of slime that is made up of certain salts, cells, or leukocytes
A condition characterized by difficulty with normal defectation