Mild diarrhea is common in ferrets because they have a short, inefficient intestinal tract that is very sensitive to changes in diet. Ferrets often eat non-nutritive substances, such as pieces of cloth or rubber. If they manage to pass the foreign body through their intestine, they often pass green mucous with it. Green mucous is not characteristic of any particular disease in a ferret, it just shows that something has irritated his gut lining.
Dairy products invariably cause loose stool in ferrets. Most ferrets love milk and will take medication, such as heartworm prevention tablets, in a small amount of milk. Nutritional diarrhea stops when the food that caused it is eliminated from the diet. This type of mild diarrhea is not harmful to the ferret, but it may distress you, particularly if the ferret has an accident on your best rug. Nutritional diarrhea usually lasts only a short time, and rarely causes dehydration if the ferret is at liberty to drink all the water he wants. If a ferret is given a food that causes diarrhea which lasts for several consecutive days, dehydration might result, and the stress might induce a secondary infectious diarrheal disease. Contact your veterinarian if your ferret's diarrhea is severe or prolonged.