So That It Does Not Become Thin: Digestion in Dogs

Dogs with diarrhea come to the practice regularly. How does the dog’s gastrointestinal tract work and what can cause disturbances in the digestive processes?

Diarrhea is when the water content of the feces is too high and the feces change from formed to mushy or liquid. Diarrhea can also be associated with an increased frequency of defecation.

Almost every dog ​​will experience diarrhea at some point in their lives, which is not uncommon given the work the digestive system has to perform. Accordingly, these patients are often presented in the veterinary practice. Depending on the severity, control over defecation remains or is lost. In the latter case, the pet owners will quickly go to the veterinarian, since living with their four-legged friend is severely impaired. Or to put it another way: the dirty living room carpet leads to greater suffering for the pet owner than chronic diarrhea that has existed for a long time and is dealt with outside of your own four walls. The TFA at registration has the important task of correctly classifying the severity of the disease in advance and arranging an appointment with the pet owner that is suitable in terms of time and duration. The purpose of this article is to convey the necessary “tools of the trade”. The first thing to do is “back to the basics”. To understand the various causes of diarrhea and how it affects the gastrointestinal tract, let’s first look at how a dog’s healthy digestive tract works.

Well chewed is half digested?

The answer for the dog is no. Dogs are carnivores and, unlike humans, do not have any digestive enzymes in their saliva. Its teeth are used to grab the prey, kill it and cut it or the food into swallowable portions. The saliva has the task of making these bites slippery so that they can be swallowed without any problems. Other tasks of saliva are moistening the oral cavity, regulating body temperature, and – through bactericidal components – defending against pathogens. The actual digestion process begins in the dog’s stomach.

Anatomy and physiology of the gastrointestinal tract

1. The Stomach

Like the wall of the rest of the gastrointestinal tract, the stomach wall consists of four layers. The outer, smooth layer facing the rest of the intestines is called the tunica serosa. Normally, it produces small amounts of fluid and allows the abdominal intestines to slide against each other as smoothly as possible. The portion of the serosa lying on the abdominal wall is called the peritoneum. In the event of inflammation of the peritoneum (peritonitis) or congestion, fluid production can increase sharply and fluid builds up in the abdominal cavity (ascites). Below the serosa is the tunica muscularis, a layer consisting of an outer layer of longitudinal smooth muscle and an underlying layer of circular smooth muscle. Between the two muscle layers lies a network of nerve cells, the myenteric plexus. It is a largely independent (autonomous) control organ from the central nervous system, which regulates the movements (peristalsis) of the gastrointestinal tract. The muscular is responsible for mixing and transporting the food pulp. The shifting layer between the mumuscularnd and the innermost layer of the gastrointestinal tract, the mucous membrane ( tunica mucosa ), is called the tunica submucosa. It consists of loose connective tissue and also contains nerve cells as well as blood and lymphatic vessels. In the area of ​​the intestine, the nerve cells form the submucosal plexus, which controls the functions of the mucosa, such as the secretion and absorption of substances.

The gastric mucosa has glands in the area of ​​the stomach body ( fundus ), which contain so-called main, parietal, and secondary cells. The main cells produce the precursors of protein-splitting enzymes ( pepsinogens ) and a fat-degrading enzyme, lipase. The parietal cells are responsible for the production of hydrochloric acid (HCl) and the secretion of the intrinsic factor responsible. Hydrochloric acid lowers the pH in the stomach to values ​​of 1-3 pH. Values ​​at which proteins denature, ie they are destroyed to such an extent that they lose their function. On the one hand, this kills many microorganisms ingested with the food, and on the other hand, denaturation is the first step in protein digestion. Intrinsic factor is needed to absorb vitamin B12 in the small intestine. The ancillary cells produce the gastric mucus that protects the stomach wall. They also excrete bicarbonate (HCO  ), which buffers the H + ions in the stomach acid and thus also serves to protect the stomach wall. Lying in the area of ​​the stomach exit ( pylorus ). G cells secrete the hormone gastrin, which leads to the release of HCl from the parietal cells.

2. The small intestine

From the stomach, the food pulp first reaches the various sections of the small intestine: duodenum ( duodenum ), jejunum ( jejunum ), hip, or ileum ( ileum ). The main task of the small intestine is to break down the individual food components into their smallest building blocks and absorb them into the intestinal cells. To be able to perform this task, the small intestine has numerous intestinal villi and the individual intestinal cells have finger-shaped protuberances on the intestinal surface ( microvilli ). The resulting immense increase in surface area is the basic prerequisite for the enormous absorption capacity of the small intestine. About two-thirds of the total fluid and electrolyte intake takes place here.

Between the intestinal villi are invaginations ( Lieberkühn crypts ) in which the renewal of the intestinal cells takes place. The renewal of the entire intestinal surface takes two to three days. In addition, there are mucus-producing goblet cells and hormone-producing cells in the Lieberkühn crypts. The number of goblet cells increases towards the anus. Most goblet cells are found in the large intestine.

The acidic chyme from the stomach is first neutralized in the duodenum. This takes place through the secretion of HCO3- from the duodenal cells and through the HCO3–containing pancreatic juice. It is formed by the exocrine part of the pancreas (the part of the pancreas that produces digestive enzymes) and contains various digestive enzymes in addition to HCO3-. These are peptidases, nucleases, amylase, and lipases. They are present in the exocrine pancreas in an inactive form to protect them from self-digestion. You get there via a duct, the ductus pancreatic, into the duodenum and, after activation, break down proteins, nucleic acids, carbohydrates, and fats into the smallest building blocks, which are absorbed by the cells in the small intestine and released into the bloodstream. Another duct that opens into the duodenum is the ductus choledochus. Through it, the bile produced in the liver and stored in the gallbladder is excreted into the duodenum. The bile contains substances that have to be excreted and bile acids that support fat digestion by breaking down the fats into small droplets. The emulsification creates many small fat droplets, the surface area of ​​which increases about a large fat droplet. As a result, the fat droplets offer the fat-splitting enzymes (lipases) a larger surface to attack and can be broken down more easily. The bile acids are resorbed in the ileum and returned to the liver with the blood ( enterohepatic circulation ).

Fat metabolism disorders occur in dogs as a result of a disease of the exocrine pancreas (exocrine pancreatic insufficiency). Due to the lack of fat-digesting enzymes (lipases), fats are excreted undigested in the feces.

In dogs, carbohydrates are digested in the front third of the small intestine. If the intestinal cells z. B. damaged by viruses or bacteria, carbohydrate digestion is impaired and undigested carbohydrates reach the subsequent small intestine sections. Since they are osmotically effective, i. H. they pull water with them, they can trigger osmotic diarrhea. They are also a welcome source of food for bacteria and can lead to bacterial overgrowth of the natural intestinal flora. Due to the bacteria-killing (bactericidal) property of the gastric juice and the rapid passage of the chyme in the small intestine, this is relatively low in germs in a healthy dog ​​in contrast to the large intestine. Any change in diet

Approximately 70% of the electrolytes sodium, chloride, magnesium, and potassium ingested with food and excreted via secretions in the gastrointestinal tract are absorbed in the small intestine. This is closely linked to the absorption of water. Resorption disorders in the small intestine, such as those that occur with diarrhea, can therefore be associated with serious losses of electrolytes and fluids.

3. The large intestine

The last section of the digestive tract is the large intestine. It begins with the appendix ( caecum ), which is followed by the colon ( large intestine ) and the rectum ( rectum ). It is densely populated with bacteria that destroy organic substances such as B. cellulose, which cannot be broken down enzymatically and degrade. It also serves to absorb electrolytes and water, thereby controlling the consistency of the feces.

The uptake of Na + and subsequently water by the colon cells is controlled by the hormone aldosterone. Low levels of Na + in the blood lead to the release of aldosterone from the adrenal cortex and increased uptake of Na+ and thus also water by the colon cells. Put simply, the presence of aldosterone leads to a harder stool consistency. As already described for the small intestine, the same applies here: Any change in the composition of the food, the retention time of the chyme in the digestive tract, and the pH value affect the natural intestinal flora and can lead to diarrhea.

The color of the feces is determined by the breakdown products of the bile pigments and the composition of the feed.


The low pH kills bacteria in the stomach and starts protein digestion. A mucus layer containing bicarbonate protects the stomach wall from self-digestion. The enzyme pepsin breaks down proteins and the enzyme lipase breaks down fats. The intrinsic factor is important for the absorption of vitamin B12 in the small intestine.

The interaction of the secretion of gastric, bile, and pancreatic juice, the absorption of food components,s and the further transport of the food pulp via the gastrointestinal peristalsis is controlled by the vegetative nervous system, breakdown products of the food and hormones of the gastrointestinal tract. Any disturbance in any of these areas can result in diarrhea.

Microbiome and immune system

The entirety of all intestinal bacteria is referred to as the microbiome. Its exact function is the subject of numerous research projects and still holds many mysteries. Its essential part in the immune system is undisputed. Recent research indicates that imbalances in the microbiome can lead to the development of autoimmune diseases such as e.g. B. can promote allergies. From this point of view, the use of antibiotics should be carefully considered, especially in young animals.

Frequently Asked Question

What makes my dog’s stool firmer?

If the dog is not very agile, its intestines will also become sluggish and the digested food cannot be optimally transported. It then builds up in the large intestine and becomes more and more solid there.

What helps against a thin stool in dogs?

Tip 1: The body loses a lot of water through soft feces. The dog must therefore always have access to fresh, clean drinking water and care should be taken to ensure that it drinks enough. Tip 2: Let your dog fast for 24 hours to avoid further straining the digestion.

How does my dog get hard stools?

Typical home remedies for solving mild constipation are milk, yogurt, linseed, psyllium husk, or oil, which should contain a relatively high proportion of paraffin oil. They all act like mild laxatives. Don’t feed your dog too many bones, as these can cause “bone poo.”

Why not feed the dog after 5 p.m.?

Here’s why you shouldn’t feed your dog after 5 p.m.: Feeding a dog after 5 p.m. can mess up his sleep cycle and upset the digestive process. The late feeding also increases the likelihood that the dog will have to go for a walk after hours.

How healthy are carrots for dogs?

Carrots: are well tolerated by most dogs and can be fed raw, grated, boiled, or steamed. They provide the dog with a large portion of beta-carotene, which has a positive effect on the health of the eyesight, skin, and hair.

How many carrots a day for the dog?

There is no quantitative limit to how many carrots your dog can eat per day. If he is not allergic to carrots, you are welcome to feed him 2-3 whole carrots without hesitation.

What yogurt for dogs?

Please only give your dog pure natural yogurt. The animal cannot do anything with sugary fruit varieties. In addition, there may be sugar substitutes in yogurt that can even be fatal to the animal.

Is oatmeal good for dogs with diarrhea?

Since oat flakes are rich in fiber, they can absorb plenty of water thanks to their swelling properties. This is extremely useful for dogs with diarrhea as it absorbs the excess liquid and improves the consistency of the stool at the same time.

Mary Allen

Written by Mary Allen

Hello, I'm Mary! I've cared for many pet species including dogs, cats, guinea pigs, fish, and bearded dragons. I also have ten pets of my own currently. I've written many topics in this space including how-tos, informational articles, care guides, breed guides, and more.

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