of Ruminant Animals

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AL 757

Special Topics in Rumen Microbiology

LEC


02

Gastrointestinal tracts(GIT) of
Ruminant Animals


Lab. of Rumen Microbiology and Biotechnology, GSNU, Korea.

Sung Sill Lee

The Gastrointestinal Tract



Different food habitats resulted in development of

diverse alimentary systems

within vertebrates:



Diversity in the anatomical features



Diversity in the digestive strategies



The GI tract is an open system
:


-

a long muscular tube extending from the mouth to the anus


-

has a continuous lining of mucus membrane



The GI tract of mammals & avian species includes:

Mouth
,
Stomach
,
Small Intestine

&
Large Intestine

Digestion

Definition:

The process by which food or feed is prepared for
absorption



It involves the breakdown of large molecules

(
polymers
) to smaller molecules (
monomers
) by

mechanical
,
enzymatic
,
chemical
, and(or)

microbial

actions

Results:

1)
A decrease in molecular size

2)
An increase in solubility

3)
The monomers can be absorbed & utilized by different cells

Diversity as Related

to Ruminants



Differ from other mammals in having a greatly

enlarged stomach (
four compartments
):



Rumen

Advantage:



Reticulum



Omasum



Abomasum



Their food is fermented first before its exposure to

the typical digestion process in the true stomach

and the intestine

Digestion of
fiber
(
cellulose

&
hemicellulose
) which
cannot be digested by mammalian enzymes

Fermentation in Other Animals

In the large intestine of various species of mammals
and birds



Most species derive little benefits from hindgut

fermentation

Because

of the very limited absorbing capacity of the

colon & cecum



Horses:

have an enlarged colon where fiber

breakdown occurs



Horses

&
ruminants

have high capacity to absorb

nutrients through the epithelium of the large

intestine


Significance ?

Diversity Among Species



The
structural

and
functional

variations in the GI

tract are related to:

1) The diet



Species variations in the dimensions and capacity of

various segments of the GI tract


Examples:


Pigs

vs
Horses

vs
Cattle

vs
Poultry


2) The feeding habits

The GI Tract of a Pig

The GI Tract of a Horse

The GI Tract of a Cow

The GI Tract of a Chicken

Capacities of Parts of the GI Tract

(% of Total)

Animal

Stomach

Small Intestine

Large Intestine

Horse



8.5



20.2



61.3


Ox



70.8


18.5



10.7

Sheep



67.9


20.4



12.7

Pig



29.2


33.5



37.3

Dog



62.3


23.3



14.4

Cat



69.5


14.6



15.9

Functions of the GI Tract

1)
Transport

of ingested food

2)
Digestion

of nutrients

3)
Absorption

of hydrolyzed products

4)
Excretion

of undigested residues and

metabolic waste

5)
Protection

against microbial infiltration




The functions are basically the same in all species

The Gastrointestinal Tract

Four basic types:

1) Simple stomached animals (non
-
ruminants)


Examples:

Pigs
,
Dogs
, and
Cats

2) Avian species


Examples:

Poultry

&
Other birds

3) Ruminants


Examples:

Sheep
&
Cattle

4) Non
-
ruminant herbivores


Examples:

Horses
&
Rabbits

The Mouth

Teeth

Function:

Mastication (
chewing
)



Chewing is accomplished by different mechanisms

in different species

Because species vary in:

2) Arrangement of jaws

3) Chewing habits

1) Type of teeth

Example:
Carnivores
versus

Herbivores

Teeth

Carnivores



-

have
simple

teeth with
cutting edges



-

little surface area


-

they tear their food (
little grinding is required
)

Herbivores


-

have at least one set of
long
teeth



(
incisors used for food gathering
)


-

have large
molars

and
pre
-
molars



-

large surface area



(
for grinding of plant material
)

Teeth

Ruminants




The jaw musculature allows for:


-

side to side motion


-

up and down motion



This allows for
circular
grinding movement



Efficient grinding is achieved by the

large

surface

area of the teeth

Teeth

Function of mastication:



Physical reduction of feed particles



Has positive effects on digestion



Decrease in particle size



Increase surface area



Increase exposure to enzymes



Increase in digestion

How?

The Stomach



A highly diversified organ in different species



Has a number of common functions

Functions:

2) Mixing

3) Decrease in particle size (some)

1) Storage

4) Chemical (
enzymatic
) digestion

The Stomach

Simple Stomached Animal (
Non
-
ruminant
)


Examples:

Pigs
,
Dogs
, and
Cats



The stomach of a pig can be divided into
4 zones



Based on the type of glands present in the epithelium

The Stomach

Ruminants

Examples:

Sheep
&
Cattle



Four chambers:

1) rumen

2) reticulum

3) omasum

4) abomasum




Have a large stomach



Rumen & reticulum:
reticulo
-
rumen



Rumen, reticulum & omasum:
forestomach



Abomasum:
true stomach

Ruminants



The ruminant stomach
digests

feed and
absorbs

its metabolites

Ruminants



The first
three

compartments are:

-

lined with
non
-
glandular keratinized stratified
epithelium

-

covered with keratinized projections
(
papillae
)



Very small in young animals



The
number

&

size

increase
with

ingestion of
solid
food

due to

mechanical

&
chemical

stimulation



Chemical stimulation is
derived from

end
-
products of
fermentation:


Volatile fatty acids [
VFA
]:


Acetate
,

propionate
&

butyrate


Ruminants


Ruminal papillae

Ruminants


Reticular papillae

Ruminants


Omasal papillae

Ruminants


Effect of diet on the number & size of papillae

A young ruminant

A well
-
fed ruminant


A starving
ruminant

Ruminants


Effect of diet on the number & size of papillae

A

B

C

D

A

Poor Quality
Feed

D

High Quality
Feed

Ruminants


Unhealthy rumen

Ruminants

The Rumen
:



Contains bacteria, protozoa & fungi



The largest compartment
(30 to 40 Gal in adult
animals)



The major site of fermentation



The major site of absorption of VFA



Near neutral
(pH 6 to 7)
Why?


-

Continuous absorption of VFA through the
rumen wall


-

Buffered by bicarbonate and phosphate
ions in
saliva

Ruminants

Saliva


Saliva produced daily

L

Humans
1.5
Pigs
15
Sheep
5 to 10
Cattle
130 to 180
Ruminants

The Reticulum:




Similar to the rumen



Characterized by its honeycomb appearance

Ruminants

The
inner surface

of the omasum


is increased by many thin folds or leaves (
laminae
)

for several reasons:


1) to enhance absorption of water, VFA & minerals


2) to reduce particle size of feed


3) to regulate digesta flow to the abomasum


4) to enhance fermentation

The Omasum:

Ruminants

The Abomasum:




The
true

stomach



Similar to that of non
-
ruminants



Separated into
3 regions
:



1) Cardiac region



2) Fundic region



3) Pyloric region




Secretes
mucus
,
HCl

&
pepsin




pH: 2 to 4




Ruminants

The Abomasum:




The mucosa is folded into spiral shape (
flaps of tissues
):

Spiral Folds

Ruminants

Development of the forestomach during growth of
ruminants:



In young ruminants, the forestomach is relatively

underdeveloped

&

nonfunctional

Why?

-

The diet is milk

-

They depend on the abomasum & small intestine for

digestion



As the calf or lamb starts to consume
solid food
, the

rumen, reticulum & omasum develop rapidly


Ruminants

Development of the forestomach in cattle:

Ruminants

Development of the forestomach in cattle:

Stomach

Newborn calf

Adult cattle

Forestomach
30%
85%
Abomasum
70%
15%
Ruminants

Development of the forestomach in sheep:

Ruminants

Esophageal groove:



In
young ruminants
, the suckled milk
by
-
passes

the

reticulo
-
rumen (
escaping the bacterial fermentation
)

and passes directly into the omasum through the

esophageal groove



Tube
-
like fold of tissue



Begins at the lower end of the esophagus



Ends at the reticulo
-
omasal orifice



Non
-
functional in older animals

Ruminants

Movement of the forestomach:



Very complex



Involves a series of contractions causing pressure

changes in the lumen



The pressure changes move the digesta through the

reticulo
-
rumen and finally to the omasum



The continuous contractions provide mixing

Ruminants

Rumination:



Contraction of the reticulum & the diaphragm



A bolus of digesta moves from the rumen to the

esophagus



The esophagus moves the bolus of digesta to the

mouth



In the mouth, the digesta is moistened with saliva,

chewed, and swallowed again



More chewing time is spent during rumination than

during eating

Ruminants

Effect of diet on rumination:



Sheep fed fine hay will ruminate 5 hours/day



Sheep fed coarse hay will ruminate 8 to 9 hours/day

Ruminants

Questions

The Stomach

Non
-
ruminant Herbivores


Examples:

Horses
&
Rabbits



Essentially the same as simple
-
stomached animals
(e.g.,
pig)

Non
-
ruminant Herbivores

Questions

The Small Intestine



Long, tubular organ in which significant amount

of
digestion

&
absorption

occurs



It is differentiated into 3 segments:

1) Duodenum:




The anterior segment (
adjacent to the stomach
)



The site at which the
bile duct

(
from the gall

bladder
) and
pancreatic ducts

enter the small

intestine


The Small Intestine

2) Jejunum:



The middle section

3) Ileum:

-

The posterior section

-

It ends at the
ileo
-
cecal junction



(where the small intestine meets the cecum)

The Functions of the Small Intestine

1) Regulation of digesta flow


(
waves of contractions forcing the contents down
)

2) Chemical & enzymatic digestion

3) Absorption of:







-

Simple sugars





-

Amino acids





-

Fatty acids





-

Minerals





-

Water


The Small Intestine

Comparative Aspects:


-

It is the least diverse of all organs of the GI tract

-

Its function is identical across species

-

Some differences in size

The Cecum & Large Intestine

The cecum:


-

It is a blind pouch

-

Varies in size & relative importance across species

-

Birds have two ceca

Colon (Large
Intestine)

Terminal Ileum

The Cecum & Large Intestine

The colon (large intestine):


-

Posterior to the ileo
-
cecal junction

Variation among animals:

Herbivores:
have enlarged cecum & proximal colon

Carnivores:
have a cecum that is small &

insignificant

The Functions of the Cecum & Colon

1) Fermentation



-

Cecum & proximal colon (
fermentation chamber
)


-

Fermentation similar to that in the rumen


-

Very important site of digestion in herbivores



(
e.g., horse & elephant
)

2) Absorption






-

Water





-

Some minerals (Na & Cl)





-

VFA

Protein & B
-
vitamins are not absorbed in
significant amounts