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B87 The Digestion
Process
Lesson Outline
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Introduction
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Types of Digestive Systems
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Ruminant Digestion
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The Digestive Process
Introduction
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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.
Infovets Educational Resources – www.infovets.com – Slide 3
Introduction
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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.
Infovets Educational Resources – www.infovets.com – Slide 4
Types of Digestive Systems
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There are basically two types of digestive systems.
Monogastric: Single stomached animals
Ruminant: Multicompartment stomach.
Infovets Educational Resources – www.infovets.com – Slide 5
Monogastric Digestive System
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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
Infovets Educational Resources – www.infovets.com – Slide 6
Dog Digestive System
Infovets Educational Resources – www.infovets.com – Slide 7
Horse Digestive System
Infovets Educational Resources – www.infovets.com – Slide 8
Swine Digestive System
Infovets Educational Resources – www.infovets.com – Slide 9
Horse & Rabbit Digestive System
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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.
Infovets Educational Resources – www.infovets.com – Slide 10
Horse & Rabbit Digestive System
Infovets Educational Resources – www.infovets.com – Slide 11
Ruminant Digestion
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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.
Infovets Educational Resources – www.infovets.com – Slide 12
Ruminant Digestion
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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.
Infovets Educational Resources – www.infovets.com – Slide 13
Ruminant Digestion
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The stomach of ruminants have four compartments:
 The rumen
 The reticulum
 The omasum
 The abomasum
Infovets Educational Resources – www.infovets.com – Slide 14
Ruminant Digestion
Infovets Educational Resources – www.infovets.com – Slide 15
Cow Digestive System
Infovets Educational Resources – www.infovets.com – Slide 16
Reticulum
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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.
Infovets Educational Resources – www.infovets.com – Slide 17
Reticulum
Infovets Educational Resources – www.infovets.com – Slide 18
Reticulum
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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.
Infovets Educational Resources – www.infovets.com – Slide 19
Rumen
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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.
Infovets Educational Resources – www.infovets.com – Slide 20
Rumen
Infovets Educational Resources – www.infovets.com – Slide 21
Rumen
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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.
Infovets Educational Resources – www.infovets.com – Slide 22
Rumen
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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.
Infovets Educational Resources – www.infovets.com – Slide 23
Omasum
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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.
Infovets Educational Resources – www.infovets.com – Slide 24
Omasum
Infovets Educational Resources – www.infovets.com – Slide 25
Abomasum
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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.
Infovets Educational Resources – www.infovets.com – Slide 26
Abomasum
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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.
Infovets Educational Resources – www.infovets.com – Slide 27
Abomasum
Infovets Educational Resources – www.infovets.com – Slide 28
Accessory Organs
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The pancreas secretes enzymes to break down fat.
The liver (largest internal organ) secretes bile, which digests fats
and stores iron.
Infovets Educational Resources – www.infovets.com – Slide 29
The Digestive Process
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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.
Infovets Educational Resources – www.infovets.com – Slide 30
Saliva
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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.
Infovets Educational Resources – www.infovets.com – Slide 31
The Digestive Process
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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.
Infovets Educational Resources – www.infovets.com – Slide 32
Small Intestine
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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.
Infovets Educational Resources – www.infovets.com – Slide 33
Small Intestine
Infovets Educational Resources – www.infovets.com – Slide 34
Villi and Nutrient Exchange
Infovets Educational Resources – www.infovets.com – Slide 35
Large Intestine
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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.
Infovets Educational Resources – www.infovets.com – Slide 36
Large Intestine
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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.
Infovets Educational Resources – www.infovets.com – Slide 37