Agriculture Reference
In-Depth Information
approximated from outside at the level of the eighth left
intercostal space.
caudal grooves, respectively. They separate the rumen into
two divisions called sacs, dorsal and ventral. Caudally the
ruminal sacs end by two blind sacs, whereas cranially
the dorsal sac continues with the ruminal atrium, and the
ventral sac ends in the ventral recess. The blind sacs are
separated from each other by the caudal groove, and from
the dorsal and ventral ruminal sacs by the coronary grooves
(dorsal and ventral, right and left). The ruminal atrium is
separated from the ruminal recess by the cranial groove.
The rumen is separated from the reticulum by the rumino-
reticular groove. The internal confi guration of the rumen
shows strong muscles grouped in pillars, and a mucosa
with one fold (rumino-reticular) and papillae. The pillars
and the fold correspond to the outside grooves (longitudi-
nal, cranial, caudal, and rumino-reticular grooves, respec-
tively). The ruminal content consists of ingesta, water,
bacteria, and protozoa to start microbial digestion, which
continues also in the reticulum and the omasum. The pro-
tozoa scavenge bacteria (primarily facultative anaerobes),
a process that helps keep the bacterial symbiont healthy.
The primary function of the rumen is to mince the
ingesta, to mix it with water, and to start the microbial
digestion. As a result, methane and carbon dioxide accu-
mulate above the ingesta in the rumino-reticular.
The Postdiaphragmatic Digestive System
This consists of segments of the gastrointestinal tract and
two annex glands, the liver and the pancreas, all located
within the abdominal cavity. The abdominal cavity is a
natural component of the body wall, outlined by the dia-
phragm cranially, the entrance into the pelvic cavity cau-
dally, the lumbar vertebrae covered by dorsal abdominal
muscles dorsally (the roof), and ventral abdominal muscles
on the lateral walls and on the ventral wall (the fl oor). The
whole cavity communicates with the pelvic cavity and are
both lined by a connective tissue layer called transverse
fascia and the parietal peritoneum. The latter sends several
peritoneal folds to connect/suspend different organs by
name of ligaments, mesentery, omenta (singular omentum),
etc., before surrounding the viscera, altogether known as
the visceral peritoneum. The pelvic cavity is outlined
between the sacrum dorsally and the two coxal bones later-
ally and ventrally. Toward the end of the pelvic cavity, the
peritoneum ends by refl ecting itself from the roof to the
fl oor of the pelvic cavity and surrounding the pelvic viscera.
There is a certain amount of connective tissue and muscle
behind the peritoneum, holding the viscera in place.
The Reticulum
The reticulum has a capacity of 1-2 liters and lies on the
fl oor of the abdominal cavity, in intimate contact with the
diaphragm. It can be seen on both sides. It looks like an
elongated ball and has a honeycomb-like mucosa. The
reticulum is separated from the ruminal atrium by the
rumino-reticular groove, that from inside corresponds to
the rumino-reticular fold. Its function is to squeeze the
ingesta by contractions that mix and move ingesta through-
out the rumen and create an explosion of contents to the
omasal canal during the second of two reticular contrac-
tions that initiate the reticulo-rumen contraction cycle.
T
HE
S
TOMACH
The stomach of the goat is pluricompartmented and
consists of four parts: rumen, reticulum, omasum, and
abomasum. The entire stomach is surrounded by visceral
peritoneum. The walls are provided with powerful muscles
lined by a specialized mucosa.
The Rumen
The rumen, with a capacity of 13-30 liters, fi lls almost the
entire left side of the abdominal cavity along with the
reticulum and part of the abomasum (Figure 6.26).
The external confi guration of the left side as well as
of the right side of all four compartments removed from
the abdominal cavity are illustrated in Figure 6.27 and
Figure 6.28 .
Two lacelike sheets of peritoneum collectively called
the walls of the greater omentum originate from both the
left and right sides of the rumen, from the longitudinal
grooves. They surround the rumen and switch the direction
from the left to the right side of the body like a hinge for
supporting most of the digestive viscera. Thus, the left wall
becomes superfi cial, and the right wall becomes deep, in
relation to one another.
The surface of the rumen is provided by two longitudi-
nal grooves (right and left), which meet in the cranial and
The Omasum
The omasum has a capacity of less than 1 liter and is
mainly located on the right side of the abdominal cavity.
It looks like a fl attened ball, and inside it has 35 folds or
laminae that are very thin and of different sizes (only three
sizes instead of four as in the other ruminants—the shortest
is absent). As a function it continues the process of squeez-
ing the ingesta and water absorption, and the omasal canal
forces the content into the omasal body. The folds of the
omasum absorb much of the fl uid from the content and,
at regular intervals, the content is passed into the
abomasum.
