The digestive system is where a dog's scavenger ancestry meets the household's kitchen, and the resulting signs, appetite changes, vomiting, diarrhea, and the rest, are the most common reasons dogs visit veterinary clinics. For Dogs (Canis lupus familiaris), a species built to eat opportunistically and digest quickly, most digestive events are brief and self-limiting, and the topic's skill is triage: what is normal, what is a passing upset, and which signs are the emergencies that the gut can produce.
The normal canine gut
The canine digestive tract is built for the carnivore-omnivore history the diet chapter describes: the stomach that holds a large meal and acidifies it aggressively, the short intestinal tract that absorbs fast, and the transit time that runs food through in hours rather than days. Normal digestion produces one to two well-formed stools a day on a consistent diet, an appetite that is enthusiastic but steady, and the quiet gut that neither gurgles its way through the night nor produces the gas that clears rooms; the variations around that baseline, the stool that softens with the rich treat, the appetite that dips in July heat, are the normal's edges rather than its exceptions.
The gut's most common visitor is the scavenger's tax: the garbage graze, the dead thing at the park, the rich treat that the household regretted, and the gastritis that follows is usually brief, self-limiting, and memorable. The diet transition rule, the week-long gradual change that the feeding chapter describes, exists because the gut's flora rebalance slowly, and the sudden switch is the self-inflicted version of the same upset.
Vomiting and regurgitation
Vomiting and regurgitation look similar and mean different things, and the distinction is diagnostic. Vomiting is an active event, the nausea, the salivating, the abdominal heaving, and it empties stomach contents that have already been digested; regurgitation is passive, the food that returns minutes after eating without heaving, straight from the esophagus, and it is the esophagus's report rather than the stomach's. The acute vomiting that follows the dietary indiscretion runs its course in a day, managed with the short fast the veterinarian approves, small amounts of water, and the bland diet reintroduction, and the dog that is bright, drinking, and asking for dinner the next morning has told the household it was the garbage.
The vomiting that earns the clinic is defined by pattern rather than volume: repeated vomiting past two or three episodes, the vomiting with blood or the coffee-ground material that means bleeding, the vomiting with the lethargy and the abdominal pain, and the vomiting that accompanies the bloated, firm abdomen of the gastric torsion the emergency chapter describes. The chronic vomiting, the weekly event that the household has normalized, is the chronic disease screen, the food sensitivity, the inflammatory condition, the foreign body grinding slowly, and the dog that vomits every week is not a dog that vomits sometimes. The projectile or persistent vomiting of the puppy is its own emergency, because the dehydration that the hydration chapter measures moves fastest in the smallest patients.
Reading the vomit
The vomit's contents are information, and the household that photographs rather than flushes gives the veterinarian the data. The undigested food of the too-fast meal, the grass of the lawn graze, the yellow foam of the empty stomach that the once-daily feeder produces before breakfast, the bile, the blood in its fresh and coffee-ground forms, and the object that is the answer, the sock, the toy, the corn cob, each points its own direction. The foreign body's vomit is the urgent one, because the obstruction that follows the object is the surgery the emergency clinic does, and the dog that vomits repeatedly without producing anything, the unproductive retching, is the gastric torsion presentation until the examination proves otherwise.
Diarrhea and its ladder
Diarrhea runs a ladder, and its rungs are triaged by duration and contents. The acute soft stool that followed the dietary adventure resolves in a day or two on the bland diet, the boiled chicken and rice or the veterinary gastrointestinal formula, with water access kept generous; the diarrhea that persists past a couple of days, or that arrives with blood, the frank red of the colon or the black tarry evidence of upper bleeding, moves up the ladder; and the rungs above them, the diarrhea with vomiting, fever, lethargy, or the dehydration the skin and gums measure, are the same-day visit. The puppy's diarrhea is its own fast lane, because the parvovirus that the vaccination series prevents presents as the bloody dehydration that kills in days, and the puppy that has not finished its series is a clinic visit the moment the stool changes.
The chronic diarrhea, the weeks of soft stool or the pattern that waxes and wanes, is the workup rather than the wait: the fecal testing that finds the parasites and the protozoa the parasite chapter describes, the diet trials that test the sensitivities, and the inflammatory conditions that need the laboratory to name. The anal-gland contribution belongs here too, the scooting and the licking that the glands' trouble produces, and the recurrence that some dogs live with is managed rather than endured.
The bland diet and the recovery menu
The bland diet is the gut's standard recovery ration, and its recipe is simple: boiled lean chicken or lean ground beef with the fat drained, mixed with white rice or plain cooked pumpkin in the ratio that firms the stool, served in small frequent meals rather than the day's two loads. The bland period runs two to three days, the transition back to the regular food is gradual, and the probiotics that some veterinarians recommend ride alongside; what the recovery menu excludes is the rich food, the treats, and the table scraps that restart the upset the diet was ending. The commercial gastrointestinal formulas do the same work with complete nutrition behind them, and the household that keeps a can on the shelf is the one that serves the bland diet on the night it is needed rather than the morning after the store opens.
When diarrhea is an emergency
The emergency signs are short and worth memorizing: blood in volume, the black tarry stool that digested blood produces, the diarrhea with the vomiting that will not stop, the diarrhea in a puppy or a toy breed, where dehydration moves fastest, the collapse or the pale gums, and the bloated painful abdomen. The poisonings that the toxic-foods chapter lists present through the gut as well, the chocolate and the xylitol and the raisins that announce through vomiting first, and the household that connects the diarrhea to the missing grapes has a poison call to make rather than a bland diet to cook. The elderly dog's diarrhea is the slower lane but the same rule, because the senior that dehydrates decompensates faster than its bloodwork predicts.
Appetite as a vital sign
Appetite is the most sensitive daily indicator the household owns, and it reads in both directions. The appetite that fades is the classic first sign of illness, the nausea, the pain, the fever, the organ disease, and the thresholds the feeding chapter set, 24 hours for the adult, 12 for the puppy and the toy breed, are the tripwires that turn observation into appointment; the appetite that vanishes with the vomiting or the lethargy moves faster. The appetite that increases is a report too: the increased hunger of the diabetes and the Cushing's, the absorption failure of the intestinal disease, and the "always hungry" dog whose portions were cut is the arithmetic case the body-condition score settles.
The picky eater is the appetite's cultural category, and it is managed rather than diagnosed: the dog that skips meals when the household watches is negotiating, the dog that skips meals when the schedule changed is stressed, and the dog that has trained its household to chase it with toppers is the dog the free-feeding chapter described. The appetite that changes with the pain, the dental disease that makes kibble hurt, is the finding the examination makes, and the senior that eats slowly and drops food is the mouth conversation the dental chapter runs.
The gut as a daily report
The digestive system is the household's daily report on the dog's interior, and the routine that reads it is the same observation habit every health chapter uses: the appetite logged, the stool glanced at with the consistency and color noted, the vomit photographed rather than flushed, the gas and the gurgles that changed noticed. The triage ladder, normal, the passing upset, the appointment, the emergency, turns the readings into action, and the prevention half is the feeding and storage and toxin architecture the earlier chapters built: gradual transitions, measured rations, the scavenger's leave-it, and the trash that latches. The gut that is watched daily is the gut whose emergencies are caught at their first hours, and the dog whose digestion runs quietly on a good diet is the dog whose report says what every chapter here is for.