Digestion in Animals

Objectives 1- Describe the nonruminant (monogastric), ruminant, and avian digestive systems. 2- Describe the process of digestion in animals. 3- Describe the absorption of nutrients in animals.

Digestive Systems Digestion is a process that breaks feed down into simple substances that can be absorbed by the body. This usually involves mechanical, chemical and enzymes. The compounds are then absorbed into the blood stream.

Digestive tract Also known as the gastrointestinal tract or the alimentary tract. Begins at the mouth and ends at the anus.

Three kinds of digestive systems. Non-ruminant (monogastric) Ruminant (polygastric) Avian

Non-ruminant digestive systems Swine, horses & humans. Single compartment stomach. Includes, mouth, teeth, tongue, salivary glands, esophagus, stomach, small intestine, liver, pancreas, cecum, large intestine, rectum and anus.

Parts of Swine Digestive Tract

Parts of Horse Digestive System

Mouth, part of digestive system. The mouth contains the teeth, tongue, and salivary glands. Chewing action (mechanical part of digestion). Food is cut and torn in the mouth, then mixed with saliva, which is produced in three different places. Three paired sets of salivary glands, located under the lower jaw and under the ears.

Mouth Saliva contains water, mucin, bicarbonate salts and enzymes. Horse saliva does not contain enzymes. In swine, saliva contains the enzymes salivary amylase and salivary maltase.

Enzymes Enzymes work in the whole digestive process, form mouth to anus. Enzymes are organic catalysts that cause and/or speed up digestive action. However, enzymes remain unchanged in this process. A weak acid solution will halt enzyme action.

Digestion in the Mouth Saliva stimulates the taste nerves. Water moistens the feed for chewing and swallowing. Mucin lubricates the feed for swallowing. Bicarbonate salts buffer the pH in the stomach.

The Tongue The tongue gathers feed in the mouth. Directs the feed in the throat for swallowing. Mixes feed.

Esophagus A tube like passage which leads from the mouth to the stomach. Peristaltic waves send feed down the esophagus, (muscle contractions). The cardia, located at the end of the esophagus prevents feed in the stomach from coming back into the esophagus. ( non-ruminants)

Stomach Pear shaped, muscular organ, receives feed, where it is further broken down by muscle in the stomach wall. Gastric juices, secreted by the glands in the stomach wall, start to flow the moment masticated feed enter the stomach. Gastric juices have about 0.2 to 0.5 percent HCl.

Stomach The wall of the stomach is lined with muscle, this muscle churns and squeezes the feed. This action forces the liquid portion on into the small intestine. The stomach of the horse has less muscular activity than that of other species, causing an increased tendency toward digestive disorders.

Horse Stomach The stomach of a horse is smaller, compared to other species, in relation to the size of the animal. Therefore, it is more desirable to feed horses in smaller amounts at one time but provide more frequent feedings.

Small Intestine Active digestion takes place here. Proteins are further broken down Starch is changed to maltose. Fats in the feed are broken down into fatty acids glycerol and monoglycerides. Bile from the liver helps emulsify fats.

Large Intestine in Swine The cecum is the first part of the large intestine The small intestine does the majority of absorption. Cecum in swine has little or no function. The colon is the middle and largest part of the large intestine.

Large Intestine, Horses Divided into cecum, large colon, small colon and rectum. Cecum is an important organ in horses. The large intestine makes up approximately 60% of the total digestive tract. Horses can use large amounts of roughage because of the presence of bacteria in the cecum and colon.

Large Intestine, Horses IMPORTANT- because the large intestine of the horse usually contains substantial quantities of ingested material, impaction occurs easily. This impaction is the start of what horse ailment?

Large Intestine The main function of the L intestine is to absorb water from the material passing through. In the Horse, the small colon is the site of most of the water resorption.

Ruminant Digestive System Mouth Saliva of ruminants does not contain enzymes, it contains buffers which neutralize acid produced in the rumen. The rumen contents are maintained at approximately a pH of 6-6.5. This pH level promotes microbial growth in the rumen. Mature cows produce about 12 gallons of saliva per day while sheep produce 2 gal.

Ruminant Digestion Stomach. The stomach of the ruminant contains four compartments: Rumen or paunch Reticulum or honey comb Omasum or many plies. Abomasum or true stomach.

Ruminant Digestion Ruminants eat rapidly swallowing much of their feed without chewing. Solid feed goes to the rumen. The liquid part also goes into the rumen. But passes quickly to the reticulum, then through the omasum and on into the abomasum.

Esophageal Groove These two muscular folds for a passage way from the cardia, ( the end of the esophagus), to the omasum. Its major function appears to be to allow milk ingest by a nursing animal to bypass fermentation in the rumen. Serves no purpose in adult ruminants.

Bovine Digestive system Identify location and function of each of the parts of the Bovine digestive system.

Rumination After the ruminant animal has filled the rumen with feed it lies down to ruminate, (chew its cud) Cattle spend from 5-7 hours ruminating, broken up into 6-8 rumination periods. Regurgitation is the process of forcing the feed back into the mouth for chewing. This is done through series of muscular contractions and pressure in the rumen and reticulum.

Rumen Microorganisms Rumen and reticulum contain millions of microorganisms called bacteria and protozoa. Together, these tiny organisms feed on the fibrous material in the rumen. They digest cellulose and compiles starch, synthesize protein and synthesize vitamins. 50-65% of the starch is digested in the rumen.

Functions of the Rumen A large fermentation vat and account for about 50-85% of the total utilization of the digestible dry matter in the ration. Saliva mixed with feed helps control the pH of the rumen. Feed material stays in the rumen and reticulum area from about two hours to several days. Type of feed influences time, Concentrates pass more quickly than roughages.

Function of the Reticulum Lined with intersecting ridges that form honeycomblike projections. Hardware that is ingested is trapped in this area and generally do not move further through the digestive system. Feed is moved back and forth between the rumen and reticulum

Function of the Omasum The omasum grinds and squeezes the feed. Little or no digestive action. The material leaving the omasum is 60-70 percent drier than the material entering it.

Function of the Abomasum Digestion here is much the same as it is in a monogastric animal. There is little or no digestion of fat, cellulose or starch. pH level of 3.5-4.0. The feed becomes highly fluid as it passes into the small intestine.

Avian Digestive Systems Different from nonruminant and ruminant. Feed in proventriculus are secreted by the glandular stomach and mixed with feed. The feed next moves to the gizzard. Epithelium breaks the feed into smaller particles, further mixing of proventricular digestive juices with the feed in the gizzard.The end of the digestive system is the vent.

Absorption of Nutrients Absorption is the process of taking nutrients from the digested feed into the blood and lymph systems. In nonruminants most absorption takes place from the small intestine with a lesser amount being absorbed from the large intestine. In ruminants there is some absorption of nutrients through the wall of the rumen.

Absorption of Nutrients The two methods of absorption are diffusion and active transport. Diffusion is the movement of molecules from an area of high concentration to one of low concentration. Active transport is the movement of molecules from one area to another requiring the expenditure of energy. Amino acids and glucose move by active transport.

Summary Digestion is breaking feed down into simple substances that can be absorbed by the body. Digestion occurs when feeds are broken up mechanically and acted upon by enzymes and other digestive juices. Most absorption of nutrients after digestion takes place in the small intestine, although some absorption occurs in the rumen.