Diarrhoea in dogs is when they excrete soft or watery stools more than five times in a 24 hour period. Although all fresh dog faeces will smell, diarrhoea with an incredibly bad odour is usually a symptom of a serious illness. Small dogs and puppies can become dangerously dehydrated quickly, so the vet needs to be contacted right away.
For The Vet
For a vet to determine the cause of the smelly diarrhoea, he will need to be informed of other symptoms such as weight loss, increased thirst, hair loss, vomiting, coordination problems or sudden lack of energy. The vet will also need a stool sample, unless it is a suspected case of hemorrhagic gastroenteritis (HGE), where the dog needs to be taken to a veterinary clinic as soon as possible.
The most dire reason a dog can have foul-smelling diarrhoea is due to HGE. This is when some part of the intestinal tract is bleeding heavily. This can be due to illness, injury, swallowing poison, being heavily infested with parasites, having an overdose of medication or swallowing a small foreign object that has damaged the digestive tract. The dog will pass pools of blood and nothing else. The smell is because of the blood. The dog will also be in considerable pain and may bite because of it.
According to "The Veterinarian's Guide to Your Dog's Symptoms," another reason a dog can have lots of foul-smelling diarrhoea is due to exocrine pancreatic insufficiency. The smell is due to undigested food, so often the diarrhoea will smell like rotting food. Other symptoms of EPI include rapid weight loss, ravenous appetite and thin or balding coat. This is a potentially lethal condition because the dog has lost the ability to properly digest food.
According to "Dog Owner's Home Veterinary Handbook," nursing puppies that have diarrhoea that smells like sour milk but does not have any other symptoms are having difficulty digesting milk or they overindulged on mother's milk. Unless they suddenly show other symptoms such as sudden weight loss or fever, they do not need to go to the vet.
If an older dog has sour milk or garbage-scented diarrhoea, it's likely the dog got into a large quantity of human food products. If the dog seems to be in distress and is also vomiting, take him immediately to the vet. If the diarrhoea has not cleared up in one day, take him to the vet. Eating spoiled food can lead to a bacterial infection.