- Pet Nutrition Part 3: Digestion
They get most of these essential nutrients from the foods they consume. The digestive system is a very important part of an animal's overall health system because it is the part of the body that will help extract nutrients from the foods eaten to help your pet grow or give them energy.
The digestive system is a series of organs that have a specific, related function, which will extract the nutrients from the food you provide for your pet.
The organs of the digestive system are the mouth, esophagus, stomach, small intestine, and large intestine. There are also accessory organs like the liver, pancreas, and kidneys. These accessory organs will secrete digestive juices, which flow into the gastrointestinal tract, assisting the breakdown of food your pet has eaten.
You should understand the following terms:
• Digestion: the process where food is converted into substances that can be utilized by the body or removed from the body as waste. The process occurs in the gastrointestinal tract.
• Alimentary canal: this is another name for the digestive tract, from the point of ingestion to the point of excretion.
• Macromolecule: a large molecule, a biological polymer such as protein and nucleic acids.
When animals consume plants and other organisms, they are then broken down through the digestive process to extract the nutrients. On a cellular level, the molecules help your animal function. The main molecules are amino acids, nucleotides, lipid molecules, and simple sugars (carbohydrates). Protein, fat, and complex sugars (complex carbohydrates) are also ingested and broken down in the absorption process.
The requirements of each animal will differ based on energy level, movement throughout the day, whether they are pregnant or lactating, and whether they are in a growth stage.
3.1 Herbivores
Herbivores are animals that eat plant materials, such as foliage, bark, or grass.
A plant diet usually requires an adaptation that carnivores and omnivores do not have.
For example, the long necks of horses, deer, and giraffes exist because these animals need to reach their food source, which is often grass or foliage in trees and plants. These animals have flat, wide teeth, which help them grind tree bark, grass, and other plant materials versus breaking through them like carnivores must do to be able to chew meat.
Herbivores have two types of feeding strategies. The first is grazing. This is when animals go along the fields eating grass, flowers, and other edible plants. They are generally not picky eaters and will be happy with whatever is most readily available to them. Cows are grazers, as are sheep and goats.
The second Is browsing. Browsing is more like what a moose does, where specific items to eat are sought out. Browsers are much more selective in what they eat. Moose will browse for high-nutrient food rather than eat a lot of whatever is available.
Animals can be both grazers and browsers based on the availability of food.
Any herbivore is going to eat when there is food present, particularly if food is normally scarce. For example, if there is a favorite plant, an herbivore will eat it when it is available but may dine on other items when that plant is not in season. Feeding in the wild is also about eating food sources that are near water and shelter. It is only when food is scarce that most herbivores will move away from water and shelter to seek proper nutrients.
With herbivores, a high amount of intake is required to get the volume of nutrients the animal needs to survive. There are fewer nutrients in a single blade of grass than carnivores and omnivores can find in their food sources. This is why more food is necessary for such large animals. Since horses are most often pets, horses will eat grass, hay, and plants, and they can also be fed grains by their owners. Grains can provide additional nutrients, which help your horses stay healthy.
3.2 Carnivores
Carnivores are animals that eat meat mainly.
Carnivores get their nutrients by digesting organs, tissue, muscle, and skin from animals.
Animals that depend on animal flesh for their sole nutrient content are "obligate" carnivores because they must have animal flesh. In contrast, facultative carnivores can consume non-animal food as well.
Most carnivores are apex predators, meaning they are high up on the food chain.
Lions, tigers, and other cat breeds/species are carnivores. Cats do not need plants to survive, but some cats may eat grass or other plants due to boredom or to help with an upset stomach. Mainly, cats and big cats are going to look for that protein-filled meal that has plenty of nutrients for energy and growth from animal flesh.
Carnivores are happy to eat land animals or water animals; they may find fish or mammals. Some will even take on reptiles. Your domesticated cat has it a little easier as they are usually fed a full meal through processed, natural foods that are high in protein, vitamins, and essential minerals.
3.3 Omnivores
Omnivores are animals that gain nutrients and energy from a varied diet, which includes animals, plants, algae, bacteria, and fungi.
"Omni" means all, and "vorare" means to devour. This is why omnivores are considered "all eaters" capable of consuming anything that is around them. They are opportunistic. Omnivores do not have specializations or adaptations to help them acquire or process food. Pigs, bears, badgers, chipmunks, mice, rats, raccoons, squirrels, sloths, skunks, hedgehogs, and opossums are all omnivores. Omnivores will find food wherever they can as a means of maintaining their diet and health. Bears may travel great distances to rivers for the salmon spawning periods; however, they will also eat nuts, berries, and plants whenever they can. Bears hibernate, which means they need to find as much to eat in the summer as possible in order to make it through the winter. Bears will stop to eat nutrients they see, but they are still going to head to the rivers to get as many fish for the hibernation season as possible.
Dogs and cats – unlike humans, other omnivores, and herbivores – are not able to synthesize vitamin D3 in their skin. Source: petdiets.com
3.4 Monogastric Digestive System & Anatomy
The digestive tract includes the oral cavity and associated organs (lips, teeth, tongue, and salivary glands), the esophagus, and the true stomach in all species, the small intestine, the liver, the exocrine pancreas, the large intestine, and the rectum and anus.
The primary functions of the GI tract include prehension of food and water; mastication, salivation, and swallowing of food; digestion of food and absorption of nutrients; maintenance of fluid and electrolyte balance; and evacuation of waste products. These functions can be broadly characterized as:
• Motility
• Secretion
• Digestion
• Absorption
• Blood flow
• Metabolism
Food is consumed through the mouth, into the esophagus, and passed through to the stomach, to the small intestine, and into the large intestine (colon).
However, there are differences within the dog's digestive system that will impact how you should feed your pet.
For dogs, teeth are designed to bite off and chew large amounts of food to eat quickly. The adaptation is to protect the dog from losing their food to a rival dog in the pack that might try to steal their food. Dogs have hinged jaws with larger teeth than humans, which can help them ingest larger chunks of meat, fat, and bones.
Food will pass through the esophagus to the stomach. Little happens in the esophagus other than giving food a track to take into the stomach. The stomach is where the food starts to break down. The stomach contains hydrochloric acid. It will break down protein and bone. If there is any food that is not digested, the dog can regurgitate it. The natural regurgitation instinct is designed to protect your dog if it eats something the system cannot handle or if there is too much food to break down. Often, your dog will eat the food again in an attempt to get it processed correctly.
The food will then pass from the stomach into the small intestine. At this time, the food is in liquid form, or at least most of it will be. The small intestine is where most of the digestive process will occur. From this point, the food is turned into nutrients that will be absorbed by the body.
The remains then enter the large intestine (colon). The large intestine is made up of the ascending colon, transverse colon, and descending colon. It is here that water is absorbed from the feces, and the feces is stored until it passes from the animal's body.
Dogs have a shorter digestive system than other mammals. It will usually take 8-9 hours for the digestive process to complete.
The number of hours it takes for a puppy to digest their food completely is even shorter. Puppies have not gained a mature digestive system, which is why their eating requirements differ from those of adult dogs.
If there is an issue with your dog's health, it is usually apparent in the digestive system. For example, your dog's eating habits or elimination habits may change, or belly bloating can occur. These changes indicate that something may be wrong inside.
What might be happening inside is not always readily apparent. The first thing vets normally look for is blood in the stools and crystals in the urine. If these options are ruled out, then the vet will take blood samples from the veins to determine if there is a disease.
Dogs often experience stomach problems. The stomach can become distended or turned into an improper position. This can also happen with the intestines and bladder. It may occur from too much rough playing, a problem during the formation of your puppy, or an accident. If the stomach continues to become turned or distended, surgery is often the necessary procedure.
What you feed your puppy or dog will have an impact on how well your pet will digest what has been eaten.
If your dog gets into the trash can and eats waste, plastic, or other materials that are hard to digest, this can lead to health issues. You must monitor where your dog goes and what it may ingest. You want to make certain your dog is not ingesting items like large bones that could affect your dog's internal system from the mouth through to the entire digestive tract and into the bladder and other elimination systems.
Cats are different from dogs and humans in terms of the eating process. The mouth is mainly used to chunk food a little before it is swallowed. Many cats will eat the food in a relatively whole condition. This is why entire chunks are seen during regurgitation due to an upset stomach or problems digesting. The amount of food chewed depends on the type of food given. Cats in the wild are going to chew a little longer to break the food into smaller sizes for swallowing through the esophagus. Kibbles are usually processed as small food to make it easier for your indoor cat to eat.
Since cats are smaller than dogs, you have to be careful how much you feed them and the size of the food.
You also want to make certain there are no bones. Small fish bones are fine, but you never want your cat to have a chicken bone or other large bone that has not been shredded by a food processor. The esophagus is extremely difficult to conduct surgery on if your cat swallows something that it shouldn't.
The stomach, like the dog's stomach, will contain hydrochloric acid to break down the food. The stomach acid also has enzymes that are secreted by the stomach lining that help to partially digest food. Once the food has been processed as much as possible by the acid enzymes, the food will move into the small intestine.
Typically, the digestion of a cat is slower than that of a dog. It can take up to 12 hours for your cat's digestive process to move the food from the stomach into the small intestine.
The small intestine is broken into three parts: the duodenum, jejunum, and ileum. The ileum connects to the large intestine. The food will move through each part of the intestine, getting broken down into nutrients. Like the dog's digestive system, the small intestine is working to assimilate nutrients that will be absorbed through the blood and intestinal walls of the cat's body. Some nutrients are absorbed in the small intestine, but others will make their way to the large intestine. The large intestine is going to break the food down even further and separate the waste from the nutrients. All nutrients that are needed will be absorbed.
All other food is broken into urine and solid waste. The solid waste is then taken from the large intestine and GI tract and out for elimination. Urine is taken into the bladder and then eliminated.
Cats have the most problems with kidney crystals, which are sent out as waste in the urine. Cuts in this area can happen, which may lead to infections. Blood can be present in the stools if there are crystals or stones. If there is blood in the waste and vets find crystals, a change of diet is necessary. There may also be some medicine to help relieve any infection. Sometimes, surgery will be required.
Unlike dogs, cats will rarely have issues with their intestines, bladder, or stomach becoming contorted. Sometimes, cats can have a distended bladder, stomach, or intestinal regions due to gas, bloating, or a blockage of stools. A change in your cat's elimination processes, as well as eating habits, will indicate there is an issue. You need to take your pet to the vet for a check-up if there is any change in their eating or elimination behavior. You may not see what is happening inside and be unaware of their discomfort.
Your cat also has natural regurgitation techniques that may occur due to hairballs, improper food processing, or a stomach ailment.
Sometimes, the food can be too rich in certain nutrients, and your cat will regurgitate them. Some cats will eat their own vomit, but others will not. It is often a breed-selective situation. If your cat is vomiting frequently, but there are no hairballs, and you also notice issues with elimination, you should seek vet care and advice. Hairballs can be excreted in waste, but this does not happen all the time. Your cat will work on a hairball to dislodge it. Often, there is a different sound, and nothing happens. Throughout that day, your cat may try to get rid of the hairball. It may take a couple of days. You can help in this process by providing hairball-reducing food, as well as hairball treats.
The process through which an animal digests food is based on what they eat, whether they are herbivores, carnivores, or omnivores. The process may take a longer amount of time in some animals based on their type of diet. For example, herbivores may eat a lot, but their digestion process is slower than a carnivore.
With carnivores, the process can also have different timings, such as a dog with a short digestive period versus the 12 hours of a cat's digestion just in the stomach.
You need to understand the process to ascertain if there are any health issues to be worried about.
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Finally, check out our Hot Diggity Dog Blog for the other modules in this series on Pet Nutrition at: Blog