Diarrhoea that lasts more than about three weeks, or that clears and returns repeatedly, is called chronic and is not the same problem as a one-off upset stomach. It needs investigating rather than managing indefinitely at home. Weight loss, vomiting, a poor coat or reduced appetite alongside it make that assessment more urgent.
The pattern that gets normalised
Almost every household with a dog like this tells a version of the same story. The stools are soft more often than they are firm. Every few weeks there is a bad stretch, then things settle. Someone eventually decides the dog has a sensitive stomach, the family adjusts around it, and years pass.
The trouble is that a sensitive stomach is a description, not a diagnosis. It explains nothing about why, and it does not tell you whether the underlying process is doing harm in the background. Some causes of chronic diarrhoea are straightforward and inexpensive to resolve. Others quietly interfere with the absorption of nutrients, and a pet can lose condition slowly enough that nobody notices until a photograph from last year makes the comparison obvious.
Where the problem sits changes what you see
One of the more useful things an owner can do before an appointment is describe the stools precisely, because small intestinal and large intestinal disease look different.
Small intestinal disease tends to produce a large volume of stool, passed perhaps three or four times a day, often watery, sometimes greasy or unusually pale, with weight loss and sometimes vomiting. There is rarely blood or mucus, and there is no straining.
Large intestinal disease produces small amounts passed frequently, sometimes eight or more times a day, often with urgency and straining, frequently with fresh red blood or a jelly-like mucus coating, and usually without much weight loss.
Note which pattern fits, count the trips outside for a few days, and photograph the stool if you can bear to. It genuinely narrows the list.
What sits behind chronic diarrhoea
The list is longer than most owners expect, and that is precisely why guessing does not work. Parasites remain a common and easily treated cause, and some are missed on a single faecal sample. Dietary intolerance and food-responsive disease account for a large share of cases. Chronic infections, disturbances in the gut bacterial population, and pancreatic problems all feature.
Beyond the gut itself, conditions affecting other organs can present this way, and in cats an overactive thyroid or kidney disease often shows up first as digestive signs. In older cats especially, intestinal cancer sits on the list and needs to be distinguished from inflammatory disease, because the two can look very similar at first.
Inflammatory bowel disease, more accurately described these days as chronic inflammatory enteropathy, is what remains once those have been worked through. It describes ongoing inflammation in the wall of the intestine, and it is diagnosed by exclusion rather than by a single test.
Why the work-up happens in a sequence
Owners sometimes find it frustrating that there is no single blood test. The sequence exists because the treatable and inexpensive causes need clearing before anyone commits to invasive testing.
Faecal testing usually comes first, often across several days because parasites are shed intermittently. Blood and urine testing follows, checking organ function, protein levels, thyroid status in cats and specific markers of pancreatic and absorptive function. Imaging assesses the thickness of the intestinal wall, the local lymph nodes and the other abdominal organs. Our diagnostic services cover each of those steps, and the results are reviewed as a whole in a medical consultation.
Where those steps do not give an answer, biopsies of the intestinal lining may be recommended, obtained either endoscopically or surgically. That is the step that distinguishes inflammatory disease from cancer, and it is the reason a definitive answer sometimes requires it.
The diet trial, and why it is done properly or not at all
A carefully structured diet trial is one of the most informative steps in the whole process, and a surprising proportion of pets respond to it. The principle is to feed a diet the immune system has not previously encountered, either a hydrolysed diet in which the protein is broken into fragments too small to provoke a reaction, or a genuinely novel protein source, for a set period.
The reason trials fail is almost never the diet. It is the extras. One flavoured chew, a dental treat, a spoonful from a plate, a flavoured tablet or a shared bowl with another pet in the house is enough to invalidate weeks of work. Everyone in the household needs to be told, including visiting family and anyone who walks the dog.
Choosing the right diet, the right duration and the right way to reintroduce foods afterward is individual work, and our nutrition counselling service exists to build exactly that plan. Our guide to pet nutrition in South Surrey covers the wider feeding picture.
What management looks like
For food-responsive cases, a suitable long-term diet often does most of the work. Where inflammation persists, treatment is tailored to what the testing showed and may include treatment directed and monitored by your veterinarian, along with attention to the gut bacterial population and to any nutrient deficiencies that have developed. Cats in particular can become deficient in certain vitamins when absorption has been impaired for a while, and correcting that can make a visible difference.
This is generally a condition that is managed rather than cured, with good stretches and occasional flares. Keep a simple diary of stool quality, appetite, weight and any flare triggers. Patterns show up in a diary that are invisible in memory, and it makes each recheck far more productive.
When it becomes urgent
Chronic problems can turn acute. Contact us the same day for diarrhoea with a lot of fresh blood, black tarry stools, repeated vomiting alongside it, obvious weakness or collapse, a painful or swollen abdomen, signs of dehydration, or a pet who will not eat or drink at all. Puppies, kittens, seniors and pets with existing conditions have less reserve and should be seen sooner. Our urgent care service handles those. Our guide on when to bring your pet to the vet sets out the wider thresholds.
One local note. Not all sudden diarrhoea is a flare of a chronic condition, and in this part of the province a dog who has been near rivers or has scavenged fish needs a different and much more urgent conversation. Our post on salmon poisoning disease covers that specific risk as the autumn runs begin. For an older pet whose digestion has changed, our South Surrey senior pet guide is worth reading beside this one.
Frequently asked questions
How long should diarrhoea last before I worry?
A single episode in an otherwise bright, eating pet can reasonably be watched for a day or so. Diarrhoea persisting beyond about three weeks, or clearing and returning repeatedly, is considered chronic and should be investigated. Do not wait that long if there is weight loss, vomiting, blood, lethargy or a refusal to eat, or if your pet is very young or elderly.
Is IBD in pets the same as IBD in people?
They share the idea of ongoing intestinal inflammation but they are not the same condition, and the human diagnostic criteria and treatments do not transfer directly. In animals the preferred term is now chronic inflammatory enteropathy, which better reflects that it is a group of conditions defined partly by what a pet responds to.
Why does my pet need so many tests?
Because chronic diarrhoea has a long list of possible causes and several of them are common, treatable and inexpensive to rule out. The sequence clears those first so that nobody proceeds to invasive testing unnecessarily. Inflammatory bowel disease is diagnosed by exclusion, so the earlier steps are what make that diagnosis meaningful rather than a guess.
Can I just switch to a sensitive stomach food from the pet shop?
It sometimes helps, but it is not the same as a proper diet trial and a partial improvement can mask what is really going on. Over-the-counter diets often contain proteins your pet has already encountered, which is exactly what a trial is designed to avoid. Speak to your veterinary team before changing, so any trial you do run actually answers the question.
Will my pet need to stay on a special diet forever?
Many do, and for food-responsive cases that diet is the treatment rather than a restriction on top of it. Some pets can have foods carefully reintroduced once they have been stable for a period, under guidance and one at a time. The plan is reviewed as your pet ages and their needs change.
My cat has been losing weight but eating well. Is that related?
It can be, and it is a combination that always deserves investigation. Weight loss despite a good appetite can reflect poor absorption from intestinal disease, an overactive thyroid, diabetes or other conditions. In cats these frequently overlap, so bloodwork alongside the digestive assessment is usually recommended rather than optional.