1. Ruminant Gastro-Intestinal Tract Anatomy

2. Rumino-reticular fold
Ruminant Gastro-Intestinal Tract Anatomy
Cardia
Entry of esophagus into the
reticulo-rumen above the reticular fold.
Reticulum on left with honeycomb.
Rumen on right with conical papillae.
Rumino-reticular fold

3. Ruminant Gastro-Intestinal Tract Anatomy
Reticulum
In the adult, the reticulum comprises approximately 5% of the
stomach capacity.
Pouch-like structure in the
forward area of the stomach.
Tissues arranged in a network
resembling a honeycomb.
Opens just below the cardia of
the esophagus.
Heavy or dense feed or foreign
objects eaten by the animal fall into
the reticulum – hardware disease.

4. Ruminant Gastro-Intestinal Tract Anatomy
Reticulum
Reticulum
The orientation of the top
picture is from the right side of
the animal’s body with the
cranial side to the right.
The orientation of the bottom
picture is from the left side of
the animal’s body.
Reticulum

5. Ruminant Gastro-Intestinal Tract Anatomy
Rumen
In the adult, the rumen comprises approximately 80% of the
stomach capacity.
Principle site of microbial fermentation
and absorption of short-chain volatile
fatty acids (VFA’s).
Absorption of VFA’s through rumen
papillae which are conical or tongue
shaped.
Presence of papillae increase surface
area for absorption.
Venous blood from the reticulum, rumen,
omasum and abomasum carries VFA’s
to the portal vein and directly to the
liver.

6. Ruminant Gastro-Intestinal Tract Anatomy
Rumen
Extends from diaphragm to pelvis
Divided by pillars (muscular folds) into sacs:
Dorsal sac
Ventral sac
Two caudal sacs

7. Ruminant Gastro-Intestinal Tract Anatomy
Rumen
Rumen papillae grow in size and number based on cellulysis.
When rate of cellulysis is high,
as with forage-based diets,
papillae are numerous and
relatively longer in length.
Mucosal pattern is unevenly
distributed, reflected by the
stratification of ingesta and
location of fermentation.
Papillae are most numerous in the mid-level region of the
rumen in the cranial sac and the dorso-caudal blindsac

8. Ruminant Gastro-Intestinal Tract Anatomy
Rumen Papillae
The rumen papillae are covered with stratified
squamous epithelium.
Rumen papillae increase the surface area
for absorption of volatile fatty acids.
Papillae are supplied by one or two arterioles
Molecules which pass through the epithelial
layer of the papillae by diffusion reach the
venules which transport the absorbed
material via the ruminal veins to the hepatic
portal vein into the liver.

9. Ruminant Gastro-Intestinal Tract Anatomy
Omasum
Almost spherical compartment located to right of rumen and reticulum
Filled with muscular folds (leaves)
Also called “book-stomach”

10. Ruminant Gastro-Intestinal Tract Anatomy
Omasum
In the adult, comprises approximately 8% of the stomach capacity.
Globe-shaped structure
containing leaves of tissue like
pages in a book.
Contains similar stratified
squamous epithelium to that
in the rumen; highly vascularized
and absorptive.
Due to folds and leaves, has
20 to 25% of the absorptive
capacity of the rumen.

11. Ruminant Gastro-Intestinal Tract Anatomy
Omasum
Function is not well understood
Perhaps has grinding action
May absorb VFA’s
May absorb water
Reticulo-omasal orifice has a role
in regulating passage of digesta
from the rumen, and thus has an
influence on intake.

12. Ruminant Gastro-Intestinal Tract Anatomy
Abomasum
Glandular compartment of ruminant stomach, located to right of rumen, ventral to omasum.

13. Ruminant Gastro-Intestinal Tract Anatomy
Abomasum
In the adult, comprises approximately 7% of the stomach capacity.
Pear-shaped and curved with the wide initial portion (fundus) next
to the omasum. Narrows gradually becoming the pyloric portion
which is tube shaped as junctions with the small intestine
Has a glandular mucosa similar to other mammals. Glandular
portion located in the fundus region. Contains HCl producing
parietal cells.
Secretes the enzyme lysozyme which breaks down bacterial cell
walls.

14. Ruminant Gastro-Intestinal Tract Anatomy
Stomach Blood Supply
Blood supply comes from the celiac artery which originates from the aorta.
The celiac artery forms six branches rather than three as in non-ruminants
Small phrenic
Hepatic – for the liver and abomasum
Several small pancreatic
Splenic which detaches to:
Right ruminal artery which is the
main arterial supply of the rumen
Left ruminal artery which detaches to the reticular artery for supply
to the reticulum
Left gastric artery which supplies the remaining portions of the
reticulum, omasum,and abomasum.

15. Ruminant Gastro-Intestinal Tract Anatomy
Stomach Blood Supply
Veins are equipped with valves and
run parallel to the arteries.
There is a dense muscular,
submucosal and mucosal network of
blood vessels in the stomach wall,
heavily developed in the prime areas
of absorption (rumen and omasum)
All venous blood from the stomach is
carried to the hepatic portal vein to the
liver.