Diarrhoea in dogs — that is, an increased frequency in the passage of liquid or semi-liquid stools — is by no means a rare occurrence. The factors potentially capable of triggering a bout of diarrhoea are numerous. The majority of the most significant diseases affecting the gastrointestinal system present, or may present, this symptom as part of their clinical picture.

"Just think of diarrhoea of parasitic origin, an event that was once almost normal in all young animals," explains Dr Michela Galgano, veterinary surgeon, "or of the kind that can manifest in the course of pancreatic insufficiency, not to mention, finally, the diarrhoeas that recognise microorganisms as the primary cause of their onset." These are precisely what the vet calls specific diarrhoeas — that is, those directly attributable to a defined cause, which always requires the utmost attention. Fortunately, this type of diarrhoea is not the most frequent. Far more common is diarrhoea from non-specific or trivial causes. Let us look at the physiological mechanisms that underlie this… embarrassing problem.

To truly understand the phenomenon of diarrhoea, it is necessary to recall a few, but fundamental, concepts of gastrointestinal physiology. Starting with the essential one of intestinal peristalsis. Peristalsis is the coordinated movement of contractions of the smooth muscle that "wraps around" the intestine. It is this movement that "propels" the food material coming from the stomach to progress along the entire intestinal tract, gradually through to its exit from the body in the form of faeces. It is a complex rhythmic contraction governed by the autonomic nervous system, but at this point the discussion would become too complicated.

It is enough for us to know that the rhythm of contractions (that is, their number per unit of time) is a highly critical factor for the correct unfolding of all the complicated digestive and absorptive mechanisms that take place inside the intestine. It is easy to understand how an acceleration of peristalsis leads to faster transit of food material, with the obvious negative consequences one can imagine. But it is not only the rhythm of contractions that determines diarrhoea. To complicate matters, there are also all the complex biochemical reactions that, at the intestinal level, govern the absorption of water. In brief, it is not wrong to say that peristaltic contractions and water absorption are linked by complex and delicate functional relationships. Which is to say that when these fragile relationships are disrupted by any factor — whether external or internal — we have two possibilities: constipation or, far more frequently, diarrhoea.

One diarrhoea, many causes

In the case of non-specific diarrhoeas, the triggering causes can be manifold. The by far most common ones are, however, relatively few; we might say they can be attributed mainly to gross dietary errors, chills, and ingestion of inappropriate material. Less frequently, causes of an emotional nature can be identified — particularly in puppies — or stressful ones, such as in male dogs in the presence of females in heat. With regard to dietary errors, it is worth emphasising once again the importance of a healthy and correct diet. Whether it is a commercial food or a home-prepared one, the doses and feeding methods recommended by the vet should always be followed. Climatic factors can also contribute to the onset of diarrhoea in our dogs.

The first cold spells, a sudden icy downpour, or, more simply, contact with a cold floor when coming from a warm environment, can all trigger a bout of diarrhoea that is destined to end as abruptly as it appeared. Finally, among the most frequent causes of non-specific acute diarrhoea episodes is the ingestion of inappropriate material. By this term we mean everything "non-food" that a dog may eat. When this does not cause far more serious trouble (obstructions, gastric or intestinal foreign body syndromes, outright poisoning), diarrhoea always appears. In these cases the phenomenon takes on a very important role: it cleanses and expels whatever is toxic and unwanted at the intestinal level. With this kind of diarrhoea, our friend does not appear to be in any way affected by the disorder, and is as lively and cheerful as usual, behaving normally. Appetite is not lacking, nor is the desire to play. A good natural product — such as carob flour, for example — can bring the episode to an end and restore normal stool consistency.

Specific forms of diarrhoea

If the situation is even slightly different from what we have outlined, or if this simple dietary measure does not produce the hoped-for results, it is certainly advisable to consult a vet. It is indeed very likely that what has affected the dog is a specific diarrhoea. In practice, this involves an inflammatory state of the intestinal mucosa of microbial, parasitic, metabolic or toxic origin. Specific diarrhoea is therefore always synonymous with enteritis — that is, inflammation. The nature and location of this inflammatory state determine much of the clinical behaviour of the disease. By way of information only, and without any claim to exhausting the subject, here is a brief overview of the causes that trigger enteritis, and therefore diarrhoea.

• Viral and bacterial infections
  These are caused by the abnormal proliferation of microbial populations that were previously in equilibrium with one another, or that have entered the body from outside.
• Parasitic infestations
  These are perhaps the most frequent causes of specific diarrhoea in very young animals. The most common culprits are worms such as ascarids, hookworms and strongyles. Coccidia and giardia, both microorganisms belonging to the class of protozoa, are increasingly often found in faecal samples from animals with diarrhoea.
• Toxic substances
  Diarrhoea is a symptom that almost invariably accompanies all forms of poisoning by chemical agents (lead, thallium, arsenic, drugs).
• Food intolerances and allergies
  These are relatively infrequent phenomena about which, to this day, not much is yet known. It is nonetheless considered that diarrhoea attributable to this type of condition is less common than is generally believed.

To conclude, let us once again stress that, while it is true that an owner can resolve a trivial bout of diarrhoea simply with hygiene measures and a little common sense, the management of specific enteritis should undoubtedly be entrusted immediately to the expertise and professionalism of a veterinary surgeon. In such cases we are dealing with a significant and persistent symptomatology that can rapidly compromise the patient's general condition. In situations of this kind, it is essential to consult a vet without delay. Because, as always in these cases, a precise and timely diagnosis can prevent far worse outcomes.