Transcript mammaliandigestionII

MAMMALIAN NUTRITION
Part II. Specialization of
carnivores and herbivores
RICHARD LLOPIS-GARCIA
A2 BIOLOGY
OBJECTIVES
 Describe
the specialization
of teeth and digestive
systems in a ruminant and a
carnivore.
Quick Draw


Quickly look at the herbivore and
carnivore skulls and draw up a table to
compare the number, shape, and possible
function of each type of tooth
Make some drawings and put labels on
them.
Two worlds


Roughly 50% of the organic carbon on earth
is tied up in cellulose. This represents an
enormous source of energy, yet vertebrate
cells do not produce the cellulases
necessary to break down this abundant
material.
However, many microbes do secrete cellulases
which allow them to utilize dietary cellulose and
other plant wall materials.
Two worlds

Cellulolytic microbes
inhabit the digestive
tract of all animals,
allowing the animal to
siphon off and
assimilate the end
products of
fermentation,
particularly short chain
or volatile fatty acids.
Two worlds


The relative value of fermentation to an animal's
nutrition pretty much depends on the size of its
fermentation vat. Fermentation occurs in the
colon of dogs and humans, but their large bowel
is rather small and the benefit they gain from
fermentation is trivial.
In contrast, herbivores make a living on
cellulose by possessing massive fermentation
vats as part of their digestive tract.
Herbivorous Strategies

Two distinct strategies have evolved.
The chief difference between the two
groups is in positioning of their
fermentation vat relative to the
stomach and small intestine:
Cranial fermentors or
ruminants

have a large, multicompartmented section
of the digestive tract between the
oesophagus and true stomach. These fore
stomachs house a very complex
ecosystem that supports fermentation.
Examples of ruminants are cattle, sheep
and deer.
Caudal fermentors or cecal
digestors

are “similar” to dogs and humans through
the stomach and small intestine, but their
large intestine, where fermentation occurs,
is complex and exceptionally large.
Examples of cecal digestors include
horses and rabbits.
The process and outcome of fermentation is essentially
identical in the rumen of a cow or the cecum of a horse.
However, the positioning of the fermentation vat in relation
to the small intestine has very important implications for
animal's physiology and nutrition. These similarities and
differences can be summarized as follows:
Function
Rumin Cecal
ants
Digestors
Ability to efficiently digest and extract
energy from cellulose
Yes
Yes
Ability to utilize dietary hexose sources
directly
No
Yes
Ability to utilize the protein from
fermentative microbes
Yes
No
Fermentation Microbiology and
Ecology

Fermentation is supported by a rich
and dense collection of microbes. Each
milliliter of rumen content contains roughly
10 to 50 billion bacteria, 1 million
protozoa and variable numbers of yeasts
and fungi.
Fermentation Microbiology and
Ecology


Fermentative microbes interact and support
one another in a complex food web, with the
waste products of some species serving as
nutrients for other species.
Fermentative bacteria representing many
genera provide a comprehensive battery of
digestive capabilities (e.g.. Cellulolytic (digest
cellulose), Hemicellulolytic (digest hemicellulose),
Amylolytic (digest starch), Proteolytic (digest
proteins), Vitamin synthesizers, Methane producers)
Digestive Anatomy in
Ruminants

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The stomach of ruminants has four
compartments: the rumen, reticulum,
omasum and abomasum
Collectively, these organs occupy
almost 3/4ths of the abdominal cavity,
filling virtually all of the left side and
extending significantly into the right.

The interior
surface of the
rumen forms
numerous
papillae that
vary in shape
and size from
short and
pointed to long
and foliate.

Reticular
epithelium is
thrown into
folds that form
polygonal cells
that give it a
reticular,
honey-combed
appearance.
Numerous
small papillae
stud the
interior floors
of these cells.

The inside of the
omasum is thrown into
broad longitudinal folds or
leaves reminiscent of the
pages in a book (a lay
term for the omasum is
the 'book'). The omasal
folds, which in life are
packed with finely ground
ingesta, have been
estimated to represent
roughly one-third of the
total surface area of the
forestomachs.
Fermentation Microbiology and
Ecology


The distribution of microbial species varies
with diet. Some of this appears to reflect
substrate availability; for example, populations
of cellulolytic bugs are depressed in animals fed
diets rich in grain.
Environmental conditions in the fermentation
vat also can have profound effects on the
microbial flora. Rumen fluid normally has a pH
between 6 and 7, but may fall if large amounts of
soluble carbohydrate are consumed.