Dog Digestive System – Organs, Hormones, Gut Health & FAQs

Dog Digestive System – Organs, Hormones, Gut Health & FAQs

The dog digestive system includes all of the organs involved in processing food. The digestive system of dogs begins with the mouth and includes the esophagus, liver, pancreas, stomach, intestines, rectum and anus. This system is vital for breaking down food into nutrients that are necessary for energy, cell repair, and growth.

As such, disorders in the digestive system of dogs can have catastrophic effects on the health and wellbeing of your pet. Maintaining a healthy digestive system helps to prevent these issues from occurring and ensures that your pet leads a happy, healthy lifestyle.

Stages of The Dog Digestive system

In order to maintain a healthy dog digestive system, it’s important to be aware of the different stages and what their significance is. Knowledge of your dog’s digestive system will also help you to identify when something is wrong, and when you need to seek out veterinary advice.

dog digestive system diagram
It’s important to be aware of the different stages of your dog’s digestive system.

Stage 1: Mouth and Esophagus

Digestion begins with the mouth. Unlike humans, the salivary glands of dogs don’t secrete many digestive enzymes – there is minimal production of amylase, but nothing more. The sole digestive function of saliva in a dog’s mouth is to lubricate the food and to protect the oral mucosa whilst eating. This means that dogs don’t need to chew their food to mix enzymes with it.

Food moves down the esophagus due to esophageal peristalsis, the contraction of circular muscle that pushes the food towards the cardiac sphincter. The esophagus consists of three structures: the upper esophageal sphincter, the body, and the lower esophageal sphincter. Two layers of striated muscle protect this organ.

saliva in a dogs mouth
Digestion begins with the mouth.

Stage 2: Stomach

Once the food arrives at the cardiac sphincter it enters the stomach. Gastric folds on the interior surface of the stomach help to grind and break down food. These folds enable the stomach’s expansion when a large meal is eaten. The stomach lining secretes four substances: mucus, hydrochloric acid, pepsinogen, and gastrin.

Gastrin is the primary hormone produces by the stomach cells. It controls hydrochloric acid secretion and stomach contractions. Hydrochloric acid interacts with pepsinogen and converts into pepsin, a digestive enzyme that breaks down proteins. Once the food is broken down by pepsin into chyme, it slowly exits through the pyloric sphincter and passes into the duodenum, the first part of the small intestine.

Stage 3: Small Intestine

The small intestine is comprised of three parts: the duodenum, ileum and the jejunum. Each segment has a different structure and function, but the collective function of the three segments is to complete digestion to allow for the absorption of nutrients.

At the beginning of the duodenum, the pancreas supplies acid-neutralizing sodium bicarbonate and digestive enzymes. Two hormones control these substances: pancreozymim and secretin, which come from cells in the small intestine. Sodium bicarbonate neutralizes the acidic chyme and helps to create an ideal environment for enzymes to function. These enzymes include amylase for carbohydrate digestion, protease for protein digestion, and lipase for fat digestion.

The villi and microvilli absorb nutrients. Microvilli produce digestive enzymes, absorb nutrients and block the absorption of any waste products. By the time the chyme reaches the end of the small intestine, up to 80 percent of the water is absorbed. Once absorption is complete, material enters the ileocaecal valve.

Stage 4: Large Intestine

The large intestine is the terminal portion of the intestinal tract. It consists of the cecum, colon, and rectum. The three main functions of the large intestine are the fermentation of indigestible food, recovery of water, and storage of feces.

The cecum absorbs the remaining water and salts and mixes the chyme with lubricating mucus. The colon, the largest portion of the large intestine, ferments unabsorbed material. Unlike the small intestine, the colon doesn’t play a major role in the digestion of food. Finally, the rectum stores the formed feces. Feces consist of about 60 to 70 percent water. The remaining percent is made up of dead bacteria, inorganic material, and food.

Ensuring a Sound Digestive System

It is vital to ensure that you look after your dog’s digestive system as it plays a huge role in your pet’s overall health and wellbeing. Selecting the best food, monitoring your dog’s stool, annual veterinary health checks and prebiotic supplements are elements you should consider when caring for your dog.

Selecting the Right Food

Are you choosing the best food for your dog? Proper nutrition is the basis for keeping your dog’s digestive system healthy. Ultimately, you need to decide what kind of food best suits your pet. This involves considering the quality of the ingredients, the type of food and the cost to fit your own budget. Doing plenty of research will help you to make the most informed decision. A balanced diet ideally contains high-quality, digestible protein, whole grains, fat, and micronutrients and is suitable for your dog’s life stage.

When changing to a new dog food, you should make the change gradually. Suddenly altering your dog’s diet is likely to cause more gastrointestinal upset. To transition to a new food, mix your dog’s current diet with the new diet. Over the course of a week, gradually decrease the amount of original food.

Noticing Your Dog's Stool

When your pet’s digestive system is healthy, his stool will show it. When something is wrong, the change in your dog’s stool is a good indicator. There are several things to look out for when monitoring your dog’s feces. The frequency of defecation matters. Healthy dogs should defecate at least once a day. Constipation may cause a dog to defecate less often. Diarrhea may cause a dog to defecate excessively.

The color of the stool should be light to dark brown. Other colors like red, black and yellow are not. Black stools indicate that blood has been digested, whereas bright red stools indicate that little or no blood has been digested. Gray or yellow indicate problems with the liver or pancreas. The color of a dog’s feces sometimes varies depending on what a dog has eaten – green, for example, sometimes indicates that your dog has eaten grass.

Firm stools are normal in dogs. Loose, hard, or runny stools are not normal. Hard feces suggest dehydration. Runny feces can point to a situation where the large intestine isn’t absorbing water during digestion.

Visiting the Vet

Every dog should visit the veterinarian once a year for a health check. This check allows your veterinarian to identify any illnesses early. This is key in the successful treatment of many diseases. If you suspect a problem with your dog’s digestive system, it’s always best to seek veterinary advice.

It’s also advisable to bring a stool sample when you suspect a digestive illness. Samples must be as fresh as possible, ideally collected within the last four to six hours. You can use a sealed ziplock bag to collect the feces. The sample should be about the size of a sugar cube or half a teaspoon.


Probiotics are live, beneficial bacteria that are given for maintaining intestinal microbial balance. When a dog is stressed or unwell, the balance between healthy and unhealthy microbes in the gut alters considerably. Probiotics usually contain bacteria that are naturally found in the dog’s gut, including Lactobacillus, Enterococcus, and Bifidobacterium. When choosing a probiotic, you should look for a few things, for example:

  • List of the specific probiotics used in the product, including the strain. Not all microbes of the Lactobacillus genus, for example, have probiotic activity. Some are anti-inflammatory, while others are immune stimulants.
  • Guaranteed analysis of the number of live strains that are in the product, and that the life of the probiotics is guaranteed at the end of its shelf life. By the time you purchase and use the product, the live bacteria may have already died.

Prebiotic fiber is a non-digestible, soluble fiber that feeds beneficial bacteria colonies in the gut. This fiber helps to increase the number of good bacteria in the digestive system. Foods like soybeans, legumes (peas, beans, lentils), oats, and beet pulp are excellent sources of prebiotic fiber. Bacteria in the gut ferment the fiber. This produces short-chain fatty acids. These serve as the primary fuel for cells in the colon. Increased amounts of short-chain fatty acids and increased numbers of good bacteria support good gastrointestinal health in dogs.

Signs of Dog Digestive System Disorders

The dog digestive system is prone to many different disorders, so it’s important to be aware of the signs when something is wrong with your pet. Because many symptoms of digestive disorders are nonspecific it is difficult to correctly diagnose your pet from home. If your dog repeatedly shows the following symptoms or exhibits more than one of these symptoms, it’s time for a trip to the vet.

Excessive Drooling

The medical term for excessive drooling in dogs is ptyalism. A common cause of ptyalism in dogs is nausea. Nausea is often triggered by irritation of the stomach and precedes vomiting. Excess saliva is produced in order to protect the mouth. Saliva also protects the throat from stomach acid. Ptyalis and vomiting, therefore, tend to come together, but excessive drooling is not always a symptom to take lightly.

Excessive drooling in dogs is also a symptom of various metabolic disorders, obstructions in the esophagus or mouth, mandibular fractures, megaesophagus, and gastric dilation, amongst many other disorders.

excessive drooling in dogs
Excess saliva is produced in order to protect the mouth.


Loose stool and diarrhea are clear signs that there is something wrong with your dog’s digestive system. Different forms can indicate different health problems.

Acute diarrhea

Acute diarrhea is a common affliction in dogs. Diarrhea is characterized by frequent watery stools, often accompanying a strong odor or color change. A dog suffering from diarrhea often develops a sore bottom. Your dog might scoot or rub their rear end across the floor or carpet to try to ease their symptoms. There are several reasons why a dog suddenly suffers from diarrhea. Stress is one of the most common causes of acute diarrhea. This includes stressors such as travel, boarding, and introduction to new pets. However, most cases are put down to these triggers:

  • Food intolerances
  • Viral or bacterial infections
  • Stress
  • Sudden dietary changes
  • Dietary indiscretion
  • Systemic illnesses
  • Intestinal parasites

Chronic diarrhea

Chronic diarrhea is diarrhea occurring for more than three weeks. This type of diarrhea is dangerous. Not only is it uncomfortable for your dog, but it also frequently causes dehydration. Symptoms found when chronic diarrhea originates in the small intestine include weight loss, gaseous sounds from the gut and black, tarry stool.

Symptoms found when chronic diarrhea comes from the large intestine include blood in the feces, straining and urgency, and pain while defecating. The small intestine produces an abnormally large volume of feces, whereas the large intestine tends to produce less, but more often. Chronic diarrhea must be addressed by a veterinarian. Your pet may require electrolytes and water via a drip to be properly rehydrated.


A lack of defecation from your pup is another strong sign that something is wrong with their digestive tract.

Acute constipation

Constipation is the inability to produce a normal amount of stools. For dogs, this should be once or twice a day. Dogs with constipation will strain to defecate, produce very hard stools, or not defecate at all. In some cases, dogs vocalize whilst straining to defecate due to the discomfort and pain involved.

Lack of fiber in the diet is a common cause of acute constipation. As with humans, a lack of fiber is often the culprit. Dietary fiber plays a vital role in the digestive health of dogs. Not only does it fuel the colon cells, but it also keeps bowel movements regular and healthy. Most commercial pet foods contain at least 5 percent crude fiber, which is usually enough for the healthy dog. If you suspect that your dog is not getting enough fiber in their diet, consider adding small amounts of high-fiber ingredients to their meal. Healthy options include green beans and wheat germ.

Dehydration is another common cause of acute constipation. This occurs when the body loses more fluid than it is taking in. Water is necessary for every vital body function, especially when it comes to digestion. In order to retain water, your dog’s digestive system will make up for the losses by producing hard stools without much water in them.

Chronic constipation

Chronic constipation results in a condition called obstipation. Obstipation occurs when dry, hard fecal matter compacts the digestive tract. This prevents the dog from defecating at all and is painful. Obstipation denotes a loss of control over the large intestine. Ultimately, it culminates into a syndrome known as megacolon. To diagnose your dog, your veterinarian will ask for their history, carry out a physical examination and conduct radiography. Treatment involves a subtotal colectomy and a high fiber diet.

dog digestive system disorders
Be aware of the signs when something is wrong with your pet.

Vomiting Or Regurgitation

Vomiting is the forceful ejection of stomach contents. There’s often a heaving motion wherein the abdominal muscles contract repeatedly before the stomach contents are expelled onto the floor. Vomit usually contains partially-digested food, yellow bile, and smells foul. Usually, when a dog vomits once and continues having normal bowel movements afterward, they recover without incident. However, chronic vomiting and vomiting alongside other worrying symptoms should be evaluated by a veterinarian.

Chronic vomiting indicates a variety of conditions, including ingestion of toxins, dietary allergies, inflammatory bowel disease, and metabolic disease. The wide array of causes means that it’s difficult to pinpoint the exact problem at home, so an appointment with your veterinarian is always the best course of action.

Regurgitation in dogs is a passive process that comes with little warning. When a dog regurgitates, chances are that they will open their mouth and expel water or undigested food that they just ate. The contents, called regurgitus, typically contain food, saliva, and mucus, but no bile. Regurgitation points to serious underlying conditions more than vomiting does and the problem usually lies with the esophagus. Pharyngeal dysphagia, vascular abnormalities, esophagitis, hypoadrenocorticism, lead toxicity, and megaesophagus are just a few of the possible causes of regurgitation in dogs. Obstructions in the esophagus also cause problems with regurgitation.

Loss Of Appetite

Loss of appetite is a highly generalized symptom of many different illnesses. On one hand, your dog could be a fussy eater. On the other, there could be a serious underlying cause. You know your pet best, and it’s up to you to determine whether this behavior is normal for them or not.

A dog who eats little or no food due to an upset stomach or emotional stressor should begin eating again within 24 hours. A loss of appetite for longer than 48 hours indicates a serious problem. Your veterinarian will give your pet intravenous fluids with electrolytes if they haven’t been drinking for over a day, and in severe cases, a feeding tube is sometimes used. Whatever the reason for this symptom is, the underlying cause must be addressed in order to resolve the problem.

Abdominal Pain And Bloating

Abdominal pain is another general symptom. Pain and bloating occur from things as simple as overeating. The symptoms also suggest a myriad of life-threatening diseases too. Because of this, it’s important that you ask for veterinary advice as soon as possible.

The signs of abdominal pain include unusual posture, drooling, tenderness and lethargy. When these symptoms occur repeatedly it’s called “acute abdomen.” Acute abdomen is a symptom of several gastrointestinal illnesses. This includes gastritis, inflammatory bowel disease, intestinal inflammation, malabsorption, and gastrointestinal obstructions.

Dog Digestive System – FAQs

Need to know something else about the dog digestive system? Our FAQ has all the answers you need. If in doubt about your dog’s digestive health, always consult your veterinarian for advice before implementing any significant changes to how you care for your dog.

How Long Does it Take for Food to Pass Through the Dog Digestive System?

On average, canines digest food much quicker than humans. While humans require 20 to 30 hours to fully digest a meal, dogs only need six to eight hours. In some cases, digestion takes up to 12 hours but is sometimes as quick as four.

Several factors determine how long it takes for your dog to digest a meal. As a general rule, the older and larger your dog is, the longer digestion takes to complete. As a dog ages, their metabolism slows down. In addition, the amount of exercise your dog has each day impacts digestion – the more energy your dog uses, the quicker their body needs to make use of the food they consume. Finally, the type of food your dog eats will also determine how quickly the digestion process completes itself. Typically, protein digests faster than grains, so a diet high in protein is more digestible.

How do you know if your Dog has Digestive problems?

Digestive problems in dogs often manifest through a wide range of symptoms. The most common symptoms include constipation, diarrhea, drooling, vomiting, regurgitation, lack of appetite, abdominal pain and bloating. Some digestive problems resolve within 24 hours. However, because more serious health conditions result in dangerous symptoms like dehydration and anorexia, you should always take your pet to the vet with any concerns.

In order to identify what digestive problems your dog is facing, your veterinarian will carry out one of or a few of these tests:

  • Complete blood cell count (CBC) – used to identify infections
  • Urinalysis – used to identify urinary tract infections and dehydration
  • Abdominal ultrasound – used to identify intestinal obstructions
  • Abdominal X-ray – used to identify intestinal obstructions

How long are a dog's intestines?

The average length of the intestines varies slightly depending on the size of the dog. However, the average length of the dog’s small intestine is reportedly 4.0 meters or 13 feet. The large intestine is larger in diameter, but shorter, measuring around 0.6 meters or 2 feet in length.

How can I Improve my Dog's Digestion?

Maintaining healthy digestion doesn’t have to be a difficult task. Fortunately, there are many ways to help your dog’s digestive system to stay healthy including a balanced diet and increased fiber. In order to improve your dog’s digestion, it’s crucial that you understand what makes a sound digestive system. A healthy dog digestive system has healthy immune cells, a good balance of beneficial bacteria in the gut is and given a suitable diet.

Always provide a balanced diet for your dog, ideally complete with high-quality protein, fat, and micronutrients. If in doubt about your pet’s diet, ask your veterinarian for advice.

Prebiotic fiber is a great addition to your pet’s diet to improve their digestion. Prebiotics are soluble fibers that feed the beneficial bacteria residing in the gut. Suitable prebiotics include soybeans, legumes, and oats. Some commercial dog food incorporates these prebiotics into their ingredients. Fiber in general also helps to resolve constipation problems.

Maintaining good dog digestive health is important for the wellbeing and health of your pet. Not only will you help to prevent potentially life-threatening illnesses, but you will ensure that your dog has the energy and nutrients to enjoy life to the fullest.