Monch monch! All dogs need to eat. Some dogs may be garbage cans and eat everything in sight and some dogs have more refined palates, and will only eat the fanciest of food. Regardless of the type of eater that they are, all dogs digest food the same way. Food goes in, undigested food comes out. But what are the steps in between? Let’s take a look at general canine nutrition, the breakdown of food in a dog's digestive system.
The main nutrients in dog food
Food provides us with the essentials for life. We get all of the tools for growth, energy and basic bodily functions from food. Just like us humans, dogs need 6 basic nutrients to live. These nutrients are protein, carbohydrates, fat (lipids), vitamins, minerals and water. Together, these nutrients provide the basis of nutrition and life.
Protein may be one of the most important nutrients for dogs. A nutrient that is required for growth and metabolism, protein is also one of the tastiest nutrients to dogs.
Protein is made up of building blocks called amino acids. There are 22 different amino acids that make up protein. The type of amino acids used and their configuration gives each protein source a unique nutritional value and function. All animals can synthesize twelve of these amino acids, deeming them as “non-essential”. Conversely, certain amino acids or “essential” amino acids must be ingested by the animal to perform normal physiological functions. The ten essential amino acids for dogs include arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
Dogs can utilize protein from multiple sources including mammals, fish, plants and even insects. There are a variety of protein sources that are added to pet food diets. Of these, beef, chicken, pork and fish are the most common animal protein feedstuffs, while soybean, peas and lentils are the most common types of plant protein feedstuffs. All of these proteins have different qualities that can influence the physiological state of an animal. Each protein source contains a different configuration of amino acids, fat content and palatability.
Carbohydrates are a controversial topic among pet owners. Some argue that they are not necessary for dogs but in all reality, there are many scientific studies showing the benefits of carbohydrates for dogs.
Carbohydrates are broken down into 2 different categories; soluble (starch) and insoluble (fibre). Starches are easily digested and broken down in the digestive tract. Soluble starch is converted to glucose in the liver and is used for energy. This energy is used by dogs for doing dog things like running and playing. Soluble fibre is usually found on the inside of plant products like grains, peas and potatoes. Milled ingredients like corn meal, pea flour, and potato starch are almost exclusively starch.
Fibre is a carbohydrate with a different function. Fibre is more slowly degraded in the digestive system and sometimes isn’t absorbed at all. That doesn’t mean it doesn’t have a function though! Since fibre is slowly digested, it sits in the gastrointestinal tract for longer. This is a good thing as it helps to keep dogs full throughout the day. Fibre also aids digestion as it is utilized by beneficial bacteria in the intestines. The bacteria use fibre to help digest other nutrients in the dog’s food. Furthermore, fibre also acts as “nature’s broom”. Fibre helps to sweep food down the digestive tract, making for better, more consistent poops. It’s not only food that fibre helps to sweep through the digestive system either. As fibre moves through the digestive tract, it helps to sweep out undigested food and pathogens like e.coli and salmonella. Some great sources of fibre are the hulls of plant products like peas and brown rice but seeds, fruits and vegetables also contain a significant amount of fibre. Find out more about fibre on our Monch Bar blog!
Just a general reminder that too much of something is never good. In high amounts, starch can raise blood sugar, putting dogs at risk for diabetes. It is usually recommended to feed dogs slowly digestible starches like brown rice, peas and lentils rather than ingredients high in available starch like corn or wheat. Conversely, if there is too much fibre in a dog’s food, it replaces the digestible nutrients and becomes just a “filler”. Avoid feeding dogs a diet that lists carbohydrates as the first ingredient. Protein should always be the first ingredient in dog food, unless it is for other health reasons.
Fat (or lipids) are often viewed in a negative light and at times it is for good reason since obesity is the number one disease among pets. However, fat is still required for life in both pets and humans. Lipids are needed by dogs for sustained energy, absorbing vitamins, keeping warm and maintaining cell membrane function. Fat is also what makes food appealing and tasty for dogs.
There are a few different types of fats. Saturated fats are the “bad” fats which raise cholesterol levels. Sources of saturated fats include fatty meat, cheese and other dairy products. Mono-unsaturated fats and polyunsaturated fats can help lower cholesterol levels and are great additions to a dog’s diet. Sources of these fats include ingredients like canola oil, sunflower oil, fish oil, and flax seeds. Trans fats are probably the worst of all the fats. Trans fat occurs when vegetable oils undergo a process called halogenation. Luckily trans fat sources are not commonly used in pet food.
It’s difficult to summarize the role of vitamins as they have hundreds of unique functions within the body. When it comes to vitamins, there are 2 different types; water and fat soluble. Water soluble vitamins have many different functions. A few examples are as follows:
- Help release energy from food
- Help produce energy during metabolism
- Help with growth and development of different body proteins and cells
- Help with wound repair
While there are fewer fat soluble vitamins than there are water soluble vitamins, they still serve many functions. A few functions of fat soluble vitamins are:
- Bone building
- Improving and maintaining vision
- Helping to absorb and store other vitamins
- Acts as antioxidants to protect against inflammation and oxidative stress
There are many different vitamins and there are a few that are considered “essential” for dogs to get through their food. The essential vitamins for dogs are:
- Vitamin A - Fat soluble vitamin
- Vitamin D - Fat soluble vitamin
- Vitamin E - Fat soluble vitamin
- Thiamine - Water soluble vitamin
- Riboflavin - Water soluble vitamin
- Pantothenic acid - Water soluble vitamin
- Pyridoxine - Water soluble vitamin
- Folic acid- Water soluble vitamin
- Niacin -Water soluble vitamin
- Vitamin B12 - Water soluble vitamin
- Choline - Water soluble vitamin
These vitamins can be found in a variety of different foods and are required by dogs at different doses. Fun fact: unlike humans, dogs can synthesize their own Vitamin C and do not need it supplemented in their food! Commercial pet food usually includes vitamin supplements to ensure that dogs are never deficient. Almost like taking your daily multivitamin!
Minerals are another micronutrient required by dogs in their food. Like vitamins, minerals have hundreds of different, unique functions for regular body function and repair. Below are the list of essential minerals that dogs need to get from their food and the function of each:
- Calcium - Needed for normal nervous and cell function. Also required for bone growth and repair.
- Phosphorus - Needed for bone and teeth formation, acid/base balance, energy metabolism, membrane function
- Sodium - Needed for proper fluid balance, nerve transmission, and muscle contraction.
- Chloride - Also needed for proper fluid balance, stomach acid.
- Magnesium - Cofactor in enzyme systems for energy production . Helps with muscle function and sodium/potassium metabolism.
- Potassium - Helps with electrolyte balance, osmotic pressure, acid/base balance, muscle contraction, and energy balance.
- Manganese - Helps activate many enzymes in metabolism and plays a role in a variety of chemical processes. It helps with protein and amino acid digestion and utilization, as well as the metabolism of cholesterol and carbohydrates.
- Iodine - The body needs iodine to make thyroid hormones. These hormones control the body's metabolism and many other important functions.
- Selenium - Important for reproduction, thyroid gland function, DNA production, and protecting the body from damage caused by free radicals and from infection.
- Zinc - Essential for enzyme function.
- Iron - Helps with oxygen carrying in the blood and muscle tissue (component of hemoglobin and myoglobin)
- Copper - Helps to make energy, connective tissues, and blood vessels. Also helps maintain the nervous and immune systems, and activates genes.
Similar to vitamins, these minerals can be found in a variety of different foods but are also supplemented in most commercial diets to ensure that there are no deficiencies and dogs do not become malnourished.
We have made it to the last and arguably the most important of the 6 essential nutrients for dogs. Hydration is happiness. 70% of a dog’s body is made up of water and it is needed in almost all bodily functions. An adult dog needs approximately 1 ounce of water per pound of body weight (or 60ml of water per kg of body weight).
Dogs can easily get water from drinking it directly from a bowl or other water source. However some dogs don’t drink as much water as they should. If that is the case, dogs can also get water from their food. Fresh-cooked and canned dog food has a significant amount of moisture (between 30-70%) and can help keep dogs hydrated.
Commercial dog food is balanced by professional companion animal nutritionists. They specifically balance each diet in order to ensure that dogs are getting all of the nutrients they need to grow and thrive. Commercial diets (whether it’s kibble, fresh-cooked or canned food) are generally much safer and healthier than diets made at home. Generally, the average pet owner cannot accurately balance the micronutrients like vitamins and minerals, which runs a high risk of dogs becoming malnourished. If you wish to make your own pet food at home, consult a companion animal nutritionist that can help you formulate a balanced diet that works for your dog.
Digestibility and bioavailability
Two very important terms in nutrition are digestibility and bioavailability. Digestibility is the proportion of ingested food that is broken down in the digestive tract and absorbed into the body. Meanwhile, bioavailability is the degree to which a specific ingested nutrient is absorbed into the body.
Different ingredients have different levels of digestibility. When it comes to meat ingredients, you want a source that is highly digestible. This means that a higher proportion of the protein will be utilized for growth and maintenance. Protein from animal sources such as muscle and organ tissue are typically more digestible than those from plant or insect sources, regardless of their overall protein content. A study by researchers Faber et al. (2010) reviewed the relative digestibility and composition of amino acids in beef, chicken, pork, pollock, and salmon. It was determined that pollock contained the highest percentage of total essential amino acids and the highest total tract digestibility, followed by salmon, beef, pork and chicken respectively.
Conversely, carbohydrates should have a moderate digestibility. If a carbohydrate is too highly digestible, it may contribute to an increase in blood sugar and increase the risk of diabetes. A balance of digestible starches and resistant fibre is the best way to go when considering carbohydrates in pet food.
Where can I find the nutritional information of my dog’s food?
Labelling of pet food is relatively the same across all brands and types of food. The governing body of pet food, the Association of American Feed Control Officials (AAFCO), requires retail and ecommerce companies to provide a base amount of nutritional information on their packaging.
On the label, you will find a list of ingredients, showing all of the ingredients used in that diet from highest to lowest inclusion. Near the ingredient list, you will also find a chart called a guaranteed analysis (GA). The GA chart provides information on the macronutrient inclusion of the food, which includes the nutrient levels of crude protein, crude fat, crude fibre, moisture and calories. To learn more about how to accurately read a GA, check out our other blog post.
Overview of dog digestion
The digestive system of a dog is somewhat similar to that of humans. Dogs are a monogastric species, which means that they have only one stomach for digestion, unlike ruminants like cows and sheep. Dogs are also considered to be obligate carnivore species, meaning that while the main component of their diet is meat or protein, they can also digest and benefit from plant products. The overall function of the digestive system is to replace materials such as water, electrolytes, vitamins/minerals, energy (from carbohydrates), and building blocks (protein/amino acids) used by other body systems, in order to maintain balance within the body.
The main parts of the canine digestive system are the mouth, esophagus, stomach, small intestine, large intestine, and rectum. There are also secondary digestive organs, which include the liver and pancreas. Each organ in the gastrointestinal system is responsible for different stages of digestion. In order for the the digestive system to function properly, it must be able to perform 4 basic functions:
- Motility - moving food in, through and out of the tract.
- Secretion - adding enzymes and chemicals to break down food.
- Digestion - breaking down materials into absorbable nutrients.
- Absorption - uptake of simple nutrients into the bloodstream.
In the mouth
Digestion begins as soon as the food hits the mouth. A dog’s mouth is designed for both the physical and chemical breakdown of food. Adult dogs have 42 permanent teeth for grinding, tearing and breaking down their food into smaller pieces. Dogs chewing their food stimulates salivary secretions to assist in chemical digestion. Saliva contains an enzyme called amylase. Amylase helps stimulate the partial breakdown of carbohydrates in the dog's food.
In the stomach
Once partial breakdown is completed in the mouth, food moves down the esophagus into the stomach. Like the mouth, the stomach participates in both physical and chemical digestion. Smooth muscle in the stomach contracts to move food around, to stimulate mixing and further physical breakdown of the food.
There are 2 specialized cells in the stomach called chief cells and parietal cells that are responsible for the chemical digestion of food. Chief cells secrete an enzyme called pepsinogen. Pepsinogen is activated to become pepsin and is responsible for the breakdown of protein in the food.
Parietal cells secrete hydrochloric acid (HCL). HCL is considered to be a moderate to strong acid with a low pH of 2. Fortunately, the stomach also secretes mucus to protect the stomach lining from the acid it produces. The primary role of HCL is to break down connective tissue and muscle protein. HCL has a dual purpose though, as it is also responsible for activating the pepsinogen from chief cells into pepsin. Overall, the stomach is the main organ for protein digestion. Once food is broken down enough, it is moved on into the small intestine.
In the intestines
The intestines are a major point for digestion and are aided by other accessory organs like the liver and pancreas. There’s 2 different sections of the intestines, the large and small intestine. Each has its own function, with its own physiological processes.
The small intestine is the first and arguably most important of the 2 sections. The small intestine is broken down into 3 different segments; the duodenum, the jejunum, and the ilium.
While protein, carbohydrate and fat digestion continues in the intestines, they do not secrete any of their own digestive enzymes. Instead digestive secretions are supplied by the pancreas and liver. The pancreas empties enzymes for digestion into the small intestines. For protein digestion, the pancreas secretes enzymes called trypsinogen, chymotrypsinogen, and procarboxypeptidase. The pancreas also secretes 2 other enzymes into the small intestine, one for carbohydrate digestion called pancreatic amylase and the other for fat digestion called pancreatic lipase. Lastly, the pancreas also secretes a substance called sodium bicarbonate in order to neutralize the acid carried into the intestines from the stomach.
The liver is another accessory organ involved in intestinal digestion. The liver produces a fluid called bile and secretes it into the duodenum via the gallbladder. Bile includes components called bile salts, which are the major reason for fat digestion. Bile salts essentially take complex fats and break them down in order to make a larger surface area for enzyme digestion.
The majority of nutrient absorption takes place in the small intestine. The lining of the small intestines are covered in protrusions called villi. The villi increase surface area of the small intestine so that there is more space for nutrient absorption. Villi also have multiple channels on their surface for nutrients that cannot be passively absorbed. Once nutrients are absorbed through the villi, they pass into the bloodstream and are transferred throughout the body.
The proportion of food that is not absorbed moves on into the large intestine. The large intestine also consists of 3 segments; the cecum, the colon and the rectum. Most of the digestion that takes place in the colon is for fibre and more resistant materials. Unlike herbivores, dogs have a shorter large intestine. This is because dogs do not eat the same volume of fibre as an animal such as a horse or cow. The large intestine is primarily responsible for bacterial digestion. The microbiome (colony of digestive bacteria) in the large intestine digest fibre by fermentation. The products of fermentation, along with water and electrolytes, are finally absorbed here. Any remaining undigested food is moved out of the large intestine and excreted out of the rectum and anus.
Food for energy and growth
You might be wondering what happens to the food once it’s absorbed from the digestive system. The absorbed nutrients enter the bloodstream and are carried throughout the body to serve their respective functions. Many of the nutrients are metabolized in the liver. Metabolism is a very complicated topic for another day. To quickly summarize, metabolism converts nutrients and compounds into usable forms such as energy, compounds for growth and other molecules for cellular function. Click here for a better overview of metabolism!
Take home message
Nutrition is a complicated process. The important thing to remember is that every dog is different and there is not one blanket diet that suits every dog. Choose the best diet that fits your dog's needs. Kabo provides a variety of diets, both fresh-cooked and kibble, with a variety of healthy ingredients. It is a great option that keeps pups happy, healthy and well fed.