Animal, Plant & Soil
Science
Lesson C3-2
Animal Digestion
Objectives
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Identify the various types of digestive
systems found in animals.
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Identify the major parts of the digestive
system and describe their functions.
What are the various types of
digestive systems found in animals?
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Knowledge of the different types of
digestive systems is critical in
selecting the proper feeds for livestock.
Understanding the chemical and physical changes
that occur during the digestive process leads to
more efficient livestock feeding.
Digestion is the process of breaking down food into
simple substances that can be absorbed by the
body.
Absorption is the process of taking the digested
parts of food into the bloodstream.
What are the various types of
digestive systems found in animals?
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The digestive system consists of the parts of the
body involved in chewing and digesting food.
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This system also moves the digested food through the
animal’s body and absorbs the products of digestion.
Different species of animals are able to digest certain types
of feeds better than others.
This difference occurs because of the various types of
digestive systems found in animals.
There are four basic types of digestive systems:
monogastric (simple), ruminant (polygastric),
pseudo-ruminant, and avian.
What are the various types of
digestive systems found in animals?
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A. The monogastric digestive system, or
simple digestive system, contains a singlechambered stomach and is the type found in
humans, swine, dogs, and cats.
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The stomach is a muscular
organ that stores ingested
food and moves it into the
small intestine.
What are the various types of
digestive systems found in animals?
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The stomach secretes acid that has a low pH of
1.5 to 2.5.
The low pH destroys most bacteria and begins to
break down the food materials.
Animals with this type of digestive system are
better adapted to the use of concentrated feeds,
such as grains, than to the use of large quantities
of roughages.
What are the various types of
digestive systems found in animals?
What are the various types of
digestive systems found in animals?
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B. The ruminant digestive system, or polygastric
digestive system, contains one large stomach
divided into four compartments and is the type found
in cattle, sheep, and goats.
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An animal with this kind of digestive system is called a
ruminant.
Due to the complexity of its digestive system, a ruminant
can make good use of roughages.
Forty-four percent of the roughages fed are digested.
The compartments of the stomach, in the order of
digestion, are rumen, reticulum, omasum, and abomasum.
What are the various types of
digestive systems found in animals?
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1. The rumen is the largest section
of the stomach and the first
compartment that the food enters.
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It accounts for approximately 60
percent of the stomach.
The rumen contains bacteria and
other microbes that promote fermentation.
The rumen is designed so that food can be
ingested, eructated (belched up), chewed, and
then swallowed again.
What are the various types of
digestive systems found in animals?
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2. The reticulum is the second segment of
the stomach.
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It is sometimes considered an extension of the
rumen.
The reticulum has honeycomb-like ridges.
It aids in keeping the food in the rumen mixed with
water and saliva until it is the right consistency.
Once the right consistency is reached, the mixture
can pass on into the lower digestive tract.
What are the various types of
digestive systems found in animals?
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3. The omasum is a small compartment that
is the main sight for water absorption.
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The particles are squeezed and dehydrated, as
well as sorted.
The compartment acts as a filter for the
abomasum.
What are the various types of
digestive systems found in animals?
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4. The abomasum, or “true stomach,” is the
site of digestion.
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It secretes gastric juices consisting of hydrochloric
acid and pepsin.
These juices kill and then digest the microbes that
have passed with the food materials from the
rumen.
The abomasum is similar to the stomach in a
monogastric animal.
What are the various types of
digestive systems found in animals?
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C. The pseudo-ruminant digestive system
is the type found in animals that eat large
amounts of roughages but do
not have stomachs with several
compartments.
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This type of digestive system
performs some of the same
functions as the type found
in ruminants.
What are the various types of
digestive systems found in animals?
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A pseudo-ruminant can utilize large amounts of
roughages because of its greatly enlarged cecum
and large intestine.
Such an animal often eats forages as well as
grains and other concentrated feeds.
Examples of pseudo-ruminants are
horses, rabbits, guinea pigs,
and hamsters.
What are the various types of
digestive systems found in animals?
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D. The avian digestive system is the type
found in poultry.
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This system differs greatly
from any other type.
Since a bird has no teeth,
no chewing is involved.
The esophagus empties
directly into the crop.
What are the various types of
digestive systems found in animals?
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The crop is where the food is stored and soaked.
From the crop, the food makes its way to the
gizzard.
The gizzard is a very muscular
organ, which normally contains
stones or grit that grinds the
food.
Digestion in the avian system
is very rapid.
What are the major parts of the
digestive system and their functions?
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The digestive system is made up
of a number of organs, which are
parts that perform specialized
functions.
The digestive system begins at the mouth, where
food enters the body, and continues to the anus,
where undigested material exits the body.
The digestive systems of most livestock are very
similar in terms of the organs they contain.
Some of the major parts of a digestive system and
their functions are:
What are the major parts of the
digestive system and their functions?
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A. Mouth and esophagus—The chewing
action of the mouth and teeth breaks, cuts,
and tears up the food.
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This increases the surface area of the
food particles and aids in the
swallowing process.
Saliva not only stimulates the taste
of the food but also contains the
enzymes salivary amylase and salivary maltase.
What are the major parts of the
digestive system and their functions?
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Enzymes are organic catalysts that speed up the
digestive process.
Salivary amylase changes starch to maltose, or
malt sugar.
Salivary maltase changes maltose to glucose.
Chewed food passes from the mouth to the
stomach through a muscular tube called the
esophagus.
What are the major parts of the
digestive system and their functions?
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B. Monogastric stomach—When food enters
the stomach of a monogastric animal, gastric
juices begin to flow.
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The fluids come from
glands in the wall of
the stomach.
The juices contain
from 0.2 to 0.5 percent hydrochloric acid.
This acid stops the action of the amylase from the
mouth.
What are the major parts of the
digestive system and their functions?
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The gastric juices also contain the enzymes
pepsin, rennin, and gastric lipase.
Pepsin breaks the proteins in the food into
proteoses and peptones.
The muscular walls of the stomach churn and
squeeze the food.
Liquids are pushed on into the small intestine.
The gastric juices then act on the solids that
remain in the stomach.
What are the major parts of the
digestive system and their functions?
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C. Ruminant stomach—The four parts of the
ruminant stomach are rumen, reticulum,
omasum, and abomasum.
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A ruminant typically eats
rapidly.
It does not chew much of
its food before swallowing.
The solid part of food goes
into the rumen.
What are the major parts of the
digestive system and their functions?
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The liquid part goes into the reticulum, then into
the omasum, and on into the abomasum.
In the rumen, the solid food is mixed and partially
broken down by bacteria.
When the rumen is full, the animal lies down.
The food is then forced back into the mouth, and
rumination occurs.
Rumination is the process of chewing the cud.
The cud is a ball-like mass of food brought up
from the stomach to be rechewed.
What are the major parts of the
digestive system and their functions?
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On average, cattle chew their
cuds about six to eight times
per day.
Five to seven hours each day
are spent in rumination.
The rumen and the reticulum contain millions
of bacteria and protozoa.
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It is the bacterial action in the rumen that allows a
ruminant to use large amounts of roughage.
The bacteria can change low-quality protein into
the amino acids needed by the animal.
What are the major parts of the
digestive system and their functions?
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Amino acids are compounds that contain
carbon, hydrogen, oxygen, and nitrogen.
They are essential for growth and
maintenance of cells.
Bacteria also produce
many of the vitamins
needed by the animal.
What are the major parts of the
digestive system and their functions?
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D. Small intestine—The partly digested food
that leaves the stomach enters the small
intestine as an acidic, semifluid, gray, pulpy
mass.
This material is called chyme.
In the small intestine, the chyme
is mixed with three digestive
juices: pancreatic juice, bile,
and intestinal juice.
What are the major parts of the
digestive system and their functions?
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1. Pancreatic juice, secreted by the
pancreas, contains the enzymes trypsin,
pancreatic amylase, pancreatic lipase, and
maltase.
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Trypsin breaks down proteins not broken down
by pepsin.
Some of the proteoses and peptones are broken
down by trypsin into peptides.
Proteoses, peptones, and peptides are
combinations of amino acids.
What are the major parts of the
digestive system and their functions?
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Proteoses are the most complex compounds, and
peptides are the simplest.
Pancreatic amylase changes starch in the food
into maltose.
Sugar and maltose are broken down even further
by maltase.
They are then changed into a simple sugar called
glucose.
Lipase works on fats in the food, changing them
into fatty acids and glycerol.
What are the major parts of the
digestive system and their functions?
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2. Bile is a yellowish-green, alkaline, bitter
liquid produced in the liver.
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Bile is stored in the
gallbladder in all animals
except the horse.
Bile aids in the digestion
of fats and fatty acids.
It also aids in the action
of the enzyme lipase.
What are the major parts of the
digestive system and their functions?
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3. Glands in the walls of the small intestine
produce intestinal juice.
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Intestinal juice is a fluid that contains peptidase,
sucrase, maltase, and lactase, all enzymes used
in digestion.
Proteoses and peptones are broken down by
peptidase into amino acids.
Starches and sugars are broken down by sucrase,
maltase, and lactase into the simple sugars
glucose, fructose, and galactose.
What are the major parts of the
digestive system and their functions?
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E. Cecum—The cecum, or “blind gut,” is
found where the small intestine joins the
large intestine.
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It has little function in
most animals.
In a pseudo-ruminant,
the roughages consumed
are digested by the
bacterial action in the cecum.
What are the major parts of the
digestive system and their functions?
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F. Large intestine—The main function of this
organ is to absorb water.
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Material not digested and absorbed in the small
intestine passes into the large intestine.
The key to absorption in the large intestine is the
small fingerlike projections on the walls, called
villi.
What are the major parts of the
digestive system and their functions?
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Food materials not digested or absorbed are
called feces.
These materials are moved through the large
intestine by muscles in the intestinal walls.
The undigested part of food is passed out of the
body through the anus, the opening at the end of
the large intestine.
Review
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What are the various types of
digestive systems found in
animals?
What are the major parts of the
digestive system and their
functions?