Digestive Systems
ANATOMY, PHYSIOLOGY & ABSORPTION OF
NUTRIENTS
ANIMAL SCIENCE I
Objectives*
 Name, locate and describe the functions of the parts
of the digestive systems of ruminant and
nonruminant animals
 Classify farm animals as ruminant and nonruminant
 Explain the relationship of types of digestive systems
to the ability of ruminants and nonruminants to
digest and absorb different classes of feed
Defining the Digestive Systems
 Digestion-the process of breaking feed down into
simple substances that can be absorbed by the body
 Absorption-taking the digested parts of feed into the
bloodstream
 Digestive System (tract)-consists of parts of the
body involved in chewing and digesting feed,
absorbing nutrients and moving digested feed
through the body
Parts of the Digestive System*
 Mouth
 Esophagus
 Small Intestine
 Large intestine
 Rectum
 Anus
 Accessory organs
 Teeth, tongue, salivary glands, liver, pancreas
Poultry Digestive System
 No teeth
 Crop and gizzard
 Ceca
 Cloaca
 Vent
Digestive Capacities
 Vary among species
 Species, age, breed and size affect capacity
 Table 5-3
 Ruminants are generally larger than nonruminants
Ruminants
 Animals that have a stomach that is divided into
several parts

Cattle, sheep, goats, llamas, bison, deer
 Can digest large quantities roughage
 This is due to the bacteria present in their digestive system.
Bacteria produce proteins, B-complex vitamins and vitamin K
Nonruminants
 Animals that have simple, one compartment
stomachs

Swine, horses, poultry
 Require high energy, low fiber rations called
concentrates
 Ruminant vs. Nonruminant usage of roughage


Cattle and sheep 44% compared to swine 22%
Horses fall in the middle at about 39%
The Ruminant Stomach
Parts
 Rumen
 Reticulum
 Omasum
 Abomasums
Rumen
 Contain millions of protozoa and bacteria
 Muscles help break the food down into smaller
particles so it is easier for bacteria to act
 No division between it and the Reticulum
Reticulum
 Hardware stomach
 Foreign objects such as wire and nails go here and
are held
 Thick walls
Omasum
 8% of stomach
 Strong muscles that grind up feed and squeeze out
some water but how much is not know
 Somewhat of a mystery area
Abomasum
 “true” stomach
 7% stomach
 Feed is mixed with gastric juices
 Digestion is carried out here just like nonruminants
How Ruminants Digest
 Eat rapidly
 Do not chew much of their feed before swallowing
 Solid part of the feed goes to the rumen; liquid part
goes into the reticulum then the omasum and on into
the abomasum
 In the rumen feed is partially broken down and
mixed by bacteria. A slow churning and mixing takes
place
 When full the animal lies down and feed is forced
back into the mouth and rumination occurs.

Cattle chew their cud 6-8 times per day
Development of the Ruminant Stomach*
 Abomasums is the only part that functions
 Young ruminants can not use roughages
 Milk goes directly the abomasums
 When born the rumen is small and found in the upper
left part of the abdomen
 After 2 months of age the rumen moves to its normal
position
 The reticulum and omasum grow and develop rapidly
 By 3 months of age the rumen has grown enough to begin
to function
Digestion in Poultry
 Possess certain special digestive organs not found in other animals
 Crop


Feed is stored and softened by saliva and secretions from the crop wall
Muscular stomach


Lined with a thick, horny membrane like material called epithelium
Feed particles are crushed and mixed with digestive juices by the gizzard
 Ceca



Two blind pouches where the small and large intestine join
About 7” long
Function is unknown but usually filled with soft, undigested food
 Cloaca

Enlarged part where the large intestine joins the vent
 Vent

Area of passage from the body for



Feces from the large intestine
Eggs from the oviduct
Urine from the kidneys
Absorption of Feed X
 Most takes place in the small intestine
 Villi-small finger shaped projections are key to
absorption because they increase the surface area of
the intestine
 As substances are absorbed by the blood capillaries
in the villi, they pass through the liver and then the
blood
 Water and dissolved minerals are also absorbed in
the small intestine
Digested Protein
 Absorbed in the form of amino acids
 Some sodium must be present for absorption to
properly occur
Digested Carbohydrates (Starches & Sugars)
 Present as monosaccharide's
 Glucose
 Fructose
 Galactose
Fiber
 In the form of short-chained fatty acids
 Adenosine triphosphate (ATP) supplies the energy
for the absorption of the monosaccharide's and fatty
acids
 Sodium must also be present
Digested Fats (soaps and glycerol)
 Form into fats again and are absorbed by the lymph
vessel in the villi.
 They pass through the thoracic duct in the neck and
into the circulatory system
Absorption in the Large Intestine
 Water and some nutrients are directly absorbed into
the bloodstream through capillaries in the intestinal
wall
 This is especially important in horses because much
of the microbial digestion of roughage occurs in the
cecum
End of the Nutrients Journey
 Most in the muscle cells
 Some are deposited in the liver
 Used to replace worn out cells and build new for
energy or stored as fat for later use
Metabolism
 Sum of the processes, both chemical and physical
that are used by living organisms and cells to handle
nutrients after they have been absorbed from the
digestive system
Process
 Anabolism—formation and repair of body tissue
 Catabolism—breakdown of body tissues into simpler
substances and waste
 Oxidation of nutrients provides energy
Summary
 Ruminants can use a lot of roughage
 They have a 4 part stomach in which bacteria
breakdown the roughages
 Nonruminants must have more concentrates such as
grain, in their ration because they have simple one
part stomachs
 Most digested feed is absorbed in the small intestine
of the animal
 Small intestine has millions of tiny villi
Assignment
 Discussion 24, 25, 27, 29-33, 35, 37
 Review Questions 1-11
 Due Friday Aug 31 end of period.