Your Dog’s Digestive System

Ever wonder why your dog eats so fast? Or why he eats inappropriate things? Or why he gets sick to his stomach? Or why his waste stinks so bad? Some of these things are normal, some are not. Find out which is which below.

It all starts with the teeth and jaws

Although many parts of a dog’s digestive system are similar to yours, their functions are just a bit different. For example, your molars are flat, allowing you to grind up your food because you are an omnivore, capable of eating and digesting just about any type of food. Your dog, on the other hand, is primarily a carnivore, so his back teeth are shaped more like blades. They are used to tear and shred meat. In addition, the dog cannot move his jaw sideways as you can because he does not typically need to grind his food.

German Shepherd Dog tearing into meat
A dog's teeth were designed for tearing meat.

Even though it looks like your dog may have fewer teeth than you do, he actually has 42 as compared to your 32. The gaps in his teeth are there to allow him to take in large hunks of meat at one time. His hinged jaw allows him to open much wider than you can. Both of these factors are important because he wants to make sure he gets enough of whatever prey his pack brought down in the wild.

Salivary enzymes

Both you and your dog use saliva to moisten food as it is chewed into small pieces. However, the make-up of the saliva is slightly different. Your saliva contains amylase, which helps to break down starchy foods into sugars before they even leave the mouth.

Your dog, on the other hand, does not have any amylase enzyme in his saliva, so the starches tend to stick to his teeth, causing plaque and tartar to build up. Your dog is much more likely to develop gum disease from the tartar, while humans tend to develop cavities from the sugars.

Your dog’s saliva contains a different enzyme, known as lysozyme, which is important in killing any bacteria that may be present in whatever your dog chooses to eat. Humans, who generally cook their food before eating it, do not have this protective enzyme.

Digestion continues in the stomach

After the food is chewed, it then passes into the esophagus where muscles work in waves to move the food into the stomach. Here we see another difference between human and canine digestion. Although both stomachs use acid to break down food, the dog’s stomach is much more acidic, carrying a pH of about 1, while a human stomach weighs in with a pH between 4 and 5. This is another protective enzyme that allows your dog to eat some really gross things and not get sick. His very acidic stomach kills most of the bacteria found in less-than-fresh roadkill and any other tasty tidbits he may find. The highly acidic environment is also more conducive to digesting bits of bone.

X-ray of a dog
Food passes from the stomach to the small intestine.

Nutrient absorption from the small intestine

As the food leaves the stomach to pass into the small intestine, it is in the form of a liquid known as chyme. The liver and pancreas secrete digestive enzymes into the small intestine to aid in the breakdown of carbohydrates and fats, and all of the nutrients from the food should be absorbed into the bloodstream before the remaining elements pass into the large intestine.

In the large intestine, bacteria break down anything that has not been fully digested and absorbed, leaving the waste products to be excreted into your yard.

Because your dog’s digestive tract is relatively short and simple, he is unable to fully process large amounts of grains and fiber. These foods simply pass through the dog, leading to more waste for you to clean up.

Compared to you, your dog keeps his food in his stomach for a longer period of time, allowing the acid to break down animal proteins, bones, and fats. This explains why the dog can live with being fed only once or twice a day. He feels full longer because the food remains in his stomach longer.

Close-up of premium dog kibble
Understanding your dog's digestive system will help you choose the best food for your dog.

Once the food clears the stomach, however, the food travels through the rest of the dog’s digestive system much more quickly than it does in yours because the dog’s intestines are only about 5% as long as yours. Food will pass through a canine digestive tract in about a day, whereas it takes up to three days to pass through yours. This is another protective feature to prevent bacteria from entering the dog’s body, but it also means you have to provide food that is easily digestible in order to get the maximum amount of nutrients absorbed in the shortest amount of time.

Why does my dog eat so fast?

Although your dog has millions more scent receptors than you do, he has thousands fewer taste buds. Where you have close to 10,000, he has fewer than 2,000. This goes back to his ancestry. Remember that dogs evolved from wolves. They had to eat fast to get their fair share when the pack was feasting, and they had to be sure to clear the area quickly before something else came along and ate them! Taste wasn’t exactly a high priority.

Cute dog in front of steak
As a carnivore, protein is the most important nutrient for your dog.

If you have more than one dog, you may be making your dog eat faster than he would if he were fed in a room alone because he reverts to that pack mentality. He wants to make sure he gets his before anyone else shoves him out of the way. If you notice your dog eating so fast that he immediately vomits it back up, try moving his dish further away from your other dogs, or try feeding him a handful at a time.

What nutrients are important for my dog?

Your dog’s number one nutritional need is protein. As you have seen from the above discussion, your dog’s entire digestive system was built to digest proteins, not the fiber and carbohydrates found as the primary ingredient in most commercial dog foods.

Your dog can’t read the food labels, so you need to do it for him. Premium dog foods such as Orijen and Life’s Abundance are made with wholesome, natural ingredients and provide high-quality protein. In addition, these foods include vitamins, minerals, anti-oxidants, omega-3 fatty acids, calcium, and even a few fruits and vegetables to balance your dog’s diet.

Because these foods are heavy on protein, you can expect to pay more for them. However, because they give your dog the things he needs, you can feed less. In addition, as the food passes through the dog’s digestive system, he will be able to absorb almost all of it, leaving less waste for you to clean up. And because the waste will not contain as much partially digested food, it should smell just a wee bit better.

Scoop of dog food
Premium dog foods are nutrient-dense so you can feed less.

Why does my dog eat poop?

This is one of the grosser habits engaged in by some dogs, but it’s more than just bad behavior. If you are feeding a cheaper, grain-based food, it is likely that much of the food is passing through your dog into his waste without ever being absorbed. This can cause a problem in that your dog must eat more to get less nutritional value. In addition, it means that his waste smells pretty much like his food. How’s he to know the difference?

This might also explain why he eats things that are not strictly food. By feeding a grain-based dog food, you are forcing him to look elsewhere for the protein he craves. When he gets into things he shouldn’t, you are just asking for an upset stomach and lots of vomit you will have to clean up.

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