B87 The Digestion Process

Lesson Outline Introduction Types of Digestive Systems Ruminant Digestion The Digestive Process

Introduction The basic function of the digestive system is to convert the basic nutrients taken in by the animal to a form that the body can use and then transport the nutrients to the cells where they are needed.

Introduction The organs that make up the digestive system are known as the gastrointestinal tract. The digestive system includes all the structures involved in the procuring, chewing, swallowing, digestion, absorption and excretion of feed.

Types of Digestive Systems There are basically two types of digestive systems. Monogastric: Single stomached animals Ruminant: Multicompartment stomach.

Monogastric Digestive System Simple stomach animals are not capable of digesting large amounts of fiber and are usually fed concentrate feeds. Monogastric animals include… Pigs Horses Rabbits Dogs Cats Birds

Dog Digestive System

Horse Digestive System

Swine Digestive System

Horse & Rabbit Digestive System The horse and rabbit have an enlargement know as a cecum that enables the animal to utilize high fiber feeds by means of microbial fermentation.

Horse & Rabbit Digestive System

Ruminant Digestion Cows, sheep, and many species of wildlife are ruminants. Any animal that regurgitates it’s food and chews it’s cud is a ruminant. The digestive system of a ruminant differs in many ways. In the mouth of ruminants there are no upper front teeth. Instead there is a dental pad that works with the lower incisors for tearing off forages and other feed stuffs.

Ruminant Digestion In the back of the mouth the upper and lower jaw have molars that enable the animal to chew on one side of the mouth at a time. Large quantities of saliva are produced. This saliva is high in phosphorus, urea nitrogen and sodium which supplies nutrients to the microorganisms in the stomach. Unlike monogastric animals there are no enzymes in the saliva.

Ruminant Digestion The stomach of ruminants have four compartments: The rumen The reticulum The omasum The abomasum

Ruminant Digestion

Cow Digestive System

Reticulum As ruminants graze, they tend to pick up hard indigestible objects such as small stones, nails and bits of wire. These heavy materials fall into the reticulum. The reticulum makes up about 5% of the total stomach capacity. The walls of the reticulum are made up of a network of sub compartments much like a honey comb. These small compartments trap and provide a storage place for hardware that does not float.

Reticulum

Reticulum This prevents dangerous objects from proceeding through the rest of the digestive tract. The reticulum also functions to store, sort and move feed back into the esophagus for regurgitation or into the rumen for further digestion. After the fluids pass through the reticulum, they move into the rumen.

Rumen The rumen, which is 80% of the total stomach, functions as a giant storage vat where food is soaked, mixed, and fermented by bacteria. It sits on the left side of the abdominal cavity it is lined with tiny papillae (tiny nipple like projection) that aid in the absorption of nutrients. Bacteria thrive in the rumen environment and function to break down fiber and cellulose.

Rumen

Rumen Volatile fatty acids are released as carbohydrates are broken down into starches and sugars. These fatty acids are absorbed through the rumen wall to provide energy. Bacteria also use nitrogen to form amino acids or protein. The bacteria can also synthesize water soluble vitamins and vitamin K.

Rumen Byproducts of the microbial activity include methane and carbon dioxide. Most of the gas is eliminated by belching. If the gases are not eliminated due to froth or foam blocking the esophagus, the animal will bloat. Bloat can be fatal. Muscles in the diaphragm are unable to expand to allow the lungs to fill with air, and the animal suffocates.

Omasum After leaving the rumen, feed travels to the omasum, witch is 8% of total stomach volume. The omasum grinds roughage using blunt muscular papillae that extend from many folds of the omasum walls.

Omasum

Abomasum The abomasum is the true stomach of the cow. It makes up about 8% of the total stomach volume. It contains glands that excrete acids and contain enzymes which break down feed in the same way the stomach in a monogastric animal works. By the time the feed reaches the abomasum, fiber has been broken down to the extent that it can be digested by the abomasum.

Abomasum By means of an esophageal groove, milk goes directly to the abomasum for digestion in young ruminants. Young animals are not born with microorganisms in the rumen, and without microorganisms, little if any digestion will occur in the rumen. It takes time and fiberous feed for microorganisms to grow.

Abomasum

Accessory Organs The pancreas secretes enzymes to break down fat. The liver (largest internal organ) secretes bile, which digests fats and stores iron.

The Digestive Process The digestive process begins at the mouth. The tongue is used to grasp food, mix it, and swallow. The teeth are used to mechanically break down the feed into smaller more digestible pieces. The mouth also contains salivary glands which excrete saliva.

Saliva Saliva contains several substances: Water to moisten the feed. Mucin to lubricate the feed. Bicarbonates to buffer acids in the feed. In monogastric animals, it contains the enzyme amylase which starts breaking down carbohydrates.

The Digestive Process The process of digestion involves both a physical and a chemical break down of feed. The walls of the stomach secrete hydrochloric acid that dissolves food. It secretes pepsin which breaks down proteins into amino acids. It secretes Renin which curdles milk. It secretes lipase which cause the breakdown of fats to fatty acids and glycerol.

Small Intestine The small intestine is a long coiled tube connecting the stomach to the large intestine. The rest of the digestion and absorption takes place here. The surface is covered with villi which provide surface area and allow absorption into the blood stream.

Small Intestine

Villi and Nutrient Exchange

Large Intestine The last organ of the digestive track is the large intestine. The first part of the large intestine consists of the cecum. The cecum serves little function on most Monogastric animals except for the horse.

Large Intestine The second part of the large intestine is the colon, which is the largest part of the organ. Its function is to provide a storage place for wastes from the digestive process. Water is removed here and further digestion occurs on fibrous materials. The rectum is the final part of the digestive system. It serves to pass waste material through to the anus where it is eliminated.