Livestock Nutrition

Livestock Nutrition Ch. 2 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 the swine digestive system. • Know location and function of each part.

Parts of Horse Digestive System • Know the location and function of each part. • Pay particular attention to the highly adapted cecum.

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 • Duodenum, the first part of the small intestine. • This is where secretions from the pancreas, liver and intestinal walls occur. • Active digestion takes place here. • Bile, secreted in the liver is stored in the gallbladder where it is secreted into the duodenum. • Horses do not have a gallbladder, therefore, bile is secreted continuously from the liver to the duodenum.

Small Intestine • The middle part of the Small Intestine is called the Jejunum. • The last part of the small intestine is called the ileum. • Nutrient absorption occurs in these two section of the small intestine.

Small Intestine • Chyme is partially digested feed in the stomach. • Chyme is an acid, semi fluid, gray, pulpy mass. • Pancreatic juice is secreted by the pancreas, a small gland located between the folds of the small intestine. • Pancreatic juice contains enzymes.

Small Intestine, Proteins • Proteins are further broken down into polypeptides oligopeptides, dipeptides and amino acids, eventually broken down into simple amino acids. • Starch is changed to maltose. • Fats in the feed are broken down into fatty acids glycerol and monoglycerides. • Bile helps emulsify fats.

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

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

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 • In all species, undigested, unabsorbed and indigestible material passes from the small intestine to the large. • 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. • Feces, material that is not absorbed or digested. • Anus, the external opening at the end of the digestive tract.

Ruminant Digestive SystemMouth • Saliva of ruminants does not contain enzymes to help digest the starches. • It contains buffers which neutralize the fatty 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: the rumen, reticulum, omasum and the abomasum. • The rumen or paunch is the first. • The reticulum or honey comb is second. • There is not a clear partition between these two compartments. • The cardia, (lower part of the esophagus is common to both compartments. • No enzymes are secreted in these tow parts.

Ruminant Digestion Stomach • The third compartment is the omasum or many plies. • It constitutes 8% of the stomach. • The omasum contains strong muscles in the walls. • The fourth and last part of the ruminant stomach is the abomasum or true stomach. • The Abomasum makes up 7% of the 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. • When closed this passage way directs feed from the esophagus directly to the omasum and when it is open the material goes into the rumen and the reticulum. • 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.

Rumination • The animal breathes in with a closed glottis. • This causes a drop in pressure in the thorax and esophagus. • The pressure in the rumen is now greater, forcing the cud into the esophagus where it is carried to the mouth, with muscular contractions. • More saliva is then mixed with the feed and it passes into the reticulum, if sufficient chewing has been done.

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.

Microorganisms • The three types of rumen bacteria are streptococci, lactobacilli and celluloytic bacteria. • 50-65% of the starch is digested in the rumen. • Protein in the rumen is converted to ammonia, organic acids and amino acids. • Most amino acids synthesized by the rumen, therefore, it is not necessary to supply large quantities of amino acids in the ration.

Functions of the Rumen • There is continual flow of feed materials into and out of the rumen. • It acts like a large fermentation vat and account for about 50-85% of the total utilization of the digestible dry matter in the ration. • Saliva which is mixed with feed helps control the pH of the rumen. • A shift of microorganisms can result from the types of feed fed.

Function of the Rumen • Feed material stays in the rumen and reticulum area from about two hours to several days. • The kind of feed influences time. Concentrates pass quicker than roughages. • Papillae line the interior wall of the rumen, they increase surface area therefore increasing the absorption ability of the rumen wall.

Function of the Rumen • Bacterial action in the rumen produces large quantities (30-50 quarts per hour) of gas, mainly CO2 and CH4. • This gas must be removed or the animal will bloat. • The gas is released through eructation, (belching). • Small amounts are absorbed by the bloodstream and then eliminated through the lungs.

Function of the Reticulum • Contains the same bacteria and protozoa as the rumen. • Lined with intersecting ridges that form honeycomblike projections. • Hardware that is ingest are 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 by regular contractions originating in the 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. • Digestive juices are added to the feed and it is moistened. • 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 • Villi are small cone-shaped projection on the wall of the small intestine. Each villi contains a network of blood capillaries through which nutrients enter the blood stream. • Protein is converted to amino acids. • Starches and sugars are converted to glucose, fructose and galactose. • Crude fiber is converted to short chained fatty acids or glucose by digestion. • These nutrients pass into the blood capillaries by osmosis through the semi permeable membranes.

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.

Metabolism • Metabolism is the sum of the chemical and physical changes continually occurring in living organisms and cells utilizing nutrients. • Anabolism is the formation and repair of body tissues. • Catabolism is the breakdown of body tissue into simpler substances.

Nutrient Transport • Nutrients in the water soluble form, are primarily carried by the blood in the animals body from where they are absorbed to where they are utilized. • Nutrients are used for maintenance, oxidation provides hear for body temperature and movement. • Nutrients are also used fro growth and fattening, fetal development, production of milk and eggs, wool and mohair and work.

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.

Livestock Nutrition