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How Dogs Digest Food

inside look at canine digestion

Your role in the canine digestion process usually involves the “before” and “after.” Here's a look at what happens in the “during” stage.

Nutrition 101

Dogs need to eat nutritious food in order to live a healthy life. The components of food that give them all the energy and raw materials they need are called “nutrients.” After dogs eat, the nutrients in the food are digested, absorbed, and processed (or “metabolized”) by the body to fulfill the dog's needs.

The ins and outs of digestion

Food gets broken down into a simple form that can be absorbed and used by the body in a process called "digestion." In mammals, this process takes place in the digestive or alimentary tract, often simply called the "gut." This is a hollow tube that the food passes through and is acted upon by acids and enzymes from organs, like the stomach and small intestine that discharge into the tube. These digestive enzymes speed up the process of hydrolysis, by which food is broken down.

The three major classes of nutrients that need to be digested are carbohydrates, protein, and fat. Other nutrients (minerals, vitamins, and water) are absorbed in more or less the same form as they are found in food. But they may need to be released from proteins, fats, or carbohydrates before they can be absorbed.

Open wide and start digesting

Digestion begins in the mouth, where food is mechanically broken down and mixed with saliva before it's swallowed. Although dogs aren't strictly carnivores, their teeth are particularly suited to meat eating, and can cut, chew, and crush food. Still, many dogs have a tendency to bolt down their food, often chewing only the toughest of foods before swallowing.

The sight and smell of food stimulates the flow of saliva, causing the dribbling and "lip smacking" often seen at mealtime. Once the food arrives in the mouth, its taste and physical presence help increase saliva production. Saliva contains mucus, a very effective lubricant that coats the food to help with swallowing.

The heart of the matter: the stomach

When food is swallowed, it passes down the esophagus, whose muscles contract with a "wave" motion called peristalsis, and arrives at the stomach within a few seconds. The stomach has several functions. It's a storage organ; it's a mixing bag (where more digestive enzymes are added to the food); and it's a regulator valve that controls the rate of flow into the small intestine. Protein digestion begins in the stomach.

The stomach secretions contain protein-digesting enzymes (proteases), hydrochloric acid, and mucus. The major enzyme, pepsin, is secreted in an inactive form, pepsinogen, to stop it from digesting the cells that produce it. Pepsinogen is activated in the stomach in the presence of hydrochloric acid (the acid produced by the stomach to help digest food), which also creates the correct environment for the enzymes to function at their optimum rate. Mucus lubricates the food, and protects the lining of the stomach wall (which is largely protein) from being digested by its own enzymes. The secretion of acid, mucus, and enzymes depends on the composition and quantity of food eaten, and is regulated by hormones and nerves.

The wall of the stomach is muscular, particularly in the pyloric region, where the stomach connects to the intestines. The stomach contents are mixed thoroughly, and push towards the pyloric sphincter — a muscular ring that acts as a regulator valve. By this time, the mixture is a thick milky liquid called chyme, and several factors control its passage into the small intestine. Strong waves in the stomach cause the pyloric sphincter to relax, and allow food to pass into the duodenum (the first part of the small intestine). Chyme passes through more easily when it's very fluid.

On the other hand, the rate of emptying is reduced by the presence of chyme, acids, fats, or irritants in the duodenum, which inhibit movements in the stomach. This ensures that the stomach contents are well mixed and sufficiently well digested before they leave the stomach. It also ensures that the small intestine doesn't receive more chyme than it can cope with efficiently.

Small intestine: Big job

The duodenum is the main site for digestion in the small intestine. Here, more enzymes — from the intestinal wall and the pancreas — are added to the chyme. The pancreas is one of the major glands of the body, and has two functions: releasing digestive enzymes into the gut and releasing hormones into the blood.

Pancreatic juice also contains sodium bicarbonate, which neutralizes the acidic chyme arriving in the duodenum, and provides an alkaline environment for optimum functioning of pancreatic and intestinal enzymes. These enzymes include proteases (for continued protein digestion), amylase (for carbohydrate digestion), and lipase (for fat digestion).

The regulation of pancreatic juice release is largely controlled by two hormones — secretin and pancreozymin, more commonly known as cholecystokinin. These are secreted from cells in the wall of the small intestine. Another important function of the pancreas is to secrete the hormone insulin into the bloodstream to control blood sugar levels.

The role of other organs

The liver is the other major organ associated with the small intestine. Bile is produced continuously in the liver, stored in the gall bladder, and passed into the gut through the bile duct when it's needed. Bile contains salts that act like detergents by turning fat into tiny globules that can then be processed by the lipase enzymes in pancreatic juice. The pigments in bile give feces their characteristic color.

The digestion of food is completed in the small intestine, and once the food has been broken down to its simplest form, it can be absorbed across the wall of the intestine and into the blood. The end products of digestion are carried to the liver, where they are metabolized. Fat is absorbed into the lymph vessels, and is later transferred to the bloodstream.

The small intestines are very long, and absorption takes place along its entire length. Folds and finger-like projections, villi, in the lining of the intestinal wall dramatically increase the surface area for absorption. In some dogs, the absorptive area of the small intestine may be as large as the floor of a small room!

Nearing the end of the journey: The large intestine

By the time the food that's been eaten reaches the large intestine, most of the nutrients have been digested and absorbed. In this part of the gut, water is absorbed, and some fermentation of dietary fiber by bacteria takes place. This process is responsible for the production of gas, often associated with flatulence.

Feces are around 60–70% water, and the rest is made up of undigested food, dead bacteria, and some inorganic material. The feces are stored in the rectum and evacuated through the anal sphincter. And, if everything in the process has gone according to plan, this will happen outside your home when you take your dog for a walk.

  • When Should You Switch Your Senior Dog to Soft Food?

    smiling lab sitting in front of brick wall


    As your dog ages, you’ll likely notice changes in your best pal’s energy levels, routine and even muzzle. Older pets may require adjustments to help them get around, exercise and live their best life as a senior. One important aspect of caring for a dog entering their golden years is diet.

    When it comes to diet, every dog has unique, individual needs, regardless of age. So, there's no one easy answer to the question of soft food versus hard food. Both types of food can provide your dog with the nutrition they need — as long as you feed your dog a high-quality dog food that’s nutritionally balanced and complete.

    two dogs eating from two bowls

    Signs Your Senior Dog May Benefit from Wet Food

    If your dog has very specific health concerns, such as aging joints or weight issues, consult with your vet for more information about what type of food best addresses your dog's needs. That being said, there are a few reasons why you may consider switching your senior dog to soft food.
     

    fluffy brown dog yawning showing teeth

    Teeth Sensitivity

    As your dog gets older, their teeth may become more sensitive, which can make chewing kibble more difficult and even uncomfortable. Switching to a soft food can help to alleviate your pet’s oral discomfort when eating.

    However, if your dog is experiencing serious pain at mealtime from a condition like tooth decay or gingivitis, switching to soft food won't remedy the problem. Make sure you talk to your vet about oral care and dental treatment.

    Digestion Aid

    Digestion begins in the mouth with saliva, so if your dog has a tendency to scarf down meals, they may not be adequately chewing the food or adding enough saliva to it. Soft food can aid with digestion because it's more easily chewed.

    Hydration Help

    It’s no surprise that wet food has a higher moisture content when compared to dry kibble. If your senior pup is prone to urinary-tract issues or simply needs a little help staying hydrated, canned dog food may be a good choice.

    girl kissing older dog on the head

    Slower Metabolism

    Aging dogs tend to have a slower metabolic rate compared to their younger years, which puts them at a higher risk of becoming overweight or obese. Many nutritionally balanced wet dog foods offer high protein content with fewer carbs than dry food, which can benefit older dogs with slower metabolism. Always talk to your vet if you have concerns about your pup’s weight.

    Picky Eaters

    While wet food may be less than appetizing to humans, the opposite is true for dogs! If your aging best friend has started turning their snout up to dry food, wet food tends to be more appealing to picky eaters. Mixing wet food and kibble offers your pup a variety of flavors and textures; try adding wet food as a topper on dry food for a real treat!

    Whether you choose dry food, soft food  or a mix of both, ask your vet before making any transition. And when it's time to switch your dog's food, remember to do it slowly — even if it's the same brand and flavor — to help prevent stomach upset and allow your dog time to adjust.

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