Food takes about eight hours to pass through the small intestine where the majority of ingested food and 80 per cent of water is absorbed. The colon then concentrates the remaining fecal matter and forms a well-shaped stool that should not contain any mucus, blood, or undigested food.
When a dog has diarrhea he/she will pass frequent, loose, unformed stools. Diarrhea is a digestive system disorder that can lead to dehydration, an imbalance of electrolytes, and possible shock if allowed to persist.
The two most common causes of diarrhea in dogs are dietary indiscretion and intestinal parasites, including roundworms, hookworms, whipworms, and threadworms. Intestinal indiscretion occurs when the natural scavenger in your dog eats indigestible substances such as garbage, decayed food, dead animals, grass, plants, plastic, paper, and any number of other foreign objects. The ingestion of rotting food can also lead to a bacterial infection resulting in runny stools.
Diarrhea can be caused by the poor absorption of nutrients caused by viruses such as parvovirus, coronavirus, and rotavirus. Malabsorption can also be caused by an intestinal defect that prevents the absorption of liquids.
Food intolerances can cause diarrhea, and some dogs seem to have difficulty tolerating certain foods including beef, pork, chicken, horsemeat, fish, eggs, spices, corn, wheat, soy, gravies, salts, spices, fats, and some commercial dog food. Food intolerances are not to be confused with food allergies, which can cause dermatitis and vomiting, but seldom cause diarrhea.
Infectious diseases, irritable bowel syndrome (IBS), and stress or excitement can also cause diarrhea. It is also a common side effect of various drugs and medications including heart medication, dewormers, and antibiotics.
Provide your dog with plenty of water and consider restricting access to food for 24 hours. See your vet if diarrhea persists or is accompanied by vomiting or fever. Look for stools that are black and tarry or contain blood and watch for signs of weakness or depression in your pet.