Page 415 - Anatomy and Physiology of Farm Animals, 8th Edition

400 / Anatomy and Physiology of Farm Animals

down the ruminant gastrointestinal tract mastication, insalivation, and swallowing.
Regurgitation is preceded by contraction of
from the forestomach. The microbial
VetBooks.ir organisms, which grew in the forestomach, the reticulum, which presumably brings
some of the heavier ingesta into proximity
are a major source of dietary protein for
ruminants. When the organisms enter the to the cardia. The sphincter at the junction
abomasum (true or glandular stomach of of the esophagus and forestomach (lower
the ruminant) and the remainder of the esophageal sphincter) relaxes as the bolus
tract, they are digested in a manner similar of food reaches it. An inspiratory move-
to digestion of protein sources in nonrumi- ment with closed glottis follows. The nega-
nants. Beneficial by‐products of microbial tive pressure produced in the thorax by this
metabolism include many water‐soluble movement is transmitted to the relatively
vitamins. thin‐walled esophagus, dilating the tho-
racic esophagus and cardia. The lower
Forestomach Motility pressure in the esophagus than in the
rumen coupled with reverse peristalsis
causes a quantity of material (semifluid
The rumen and reticulum of the adult cow ingesta) to pass through the cardia into the
normally undergo complicated sequences of esophagus and up to the mouth. The regur-
contractions that are repeated at varying fre- gitated material consists largely of rough-
quencies up to several times per minute. age and fluid, with little if any concentrate.
One pattern of contractions begins in the It is well known that whole kernels of corn
reticulum and spreads over both the dorsal may pass through the entire digestive tract
and ventral sacs of the rumen (see Fig. 20‐13). of a cow with little change in physical
This series of contractions mixes the con- appearance and yet corn is often included
tents to promote fermentation and provide in cattle diets to increase starch digestion.
force to move liquefied digesta out of the Cracking or rolling the corn can result in an
forestomach and into the abomasum. A sec- increased digestive capacity and therefore
ond pattern of contractions begins in the better feed efficiency.
caudal portion of the dorsal sac and moves Cattle average about 8 hours a day rumi-
cranially. These contractions move gases nating, with periods of activity scattered
toward the cranial part of the rumen for throughout the entire day. One rumination
eructation. Rumen contractions can easily cycle requires about 1 minute, of which 3 to
be heard by listening (preferably with a 4 seconds is used for both regurgitation and
stethoscope) to the abdomen or felt by reswallowing. Rumination appears to be
forcing the fist into the upper left flank largely reflexive, although the process can
(paralumbar fossa). Pathologic condition be interrupted or stopped voluntarily. Both
of the rumen or morbidity associated with afferent and efferent portions of the reflex
systemic diseases usually results in a are probably carried in the vagal nerves.
decreased rate or complete cessation of Contact of roughage with the wall of the
rumen movements. reticulum and near the cardia is likely the
Rumination permits an animal to for-
age and ingest food rapidly, but finish major stimulus for rumination.
chewing it later. This process entails regur-
gitation of the food whereby the food is Reticular, or Esophageal, Groove
returned to the mouth from the forestom-
ach. Once back in the mouth, remastica- In young ruminants, nursing and afferents
tion (rechewing) with reinsalivation from the pharynx appear to stimulate reflex
(mixing with more saliva) occurs, and closure of the groove, which causes milk to
finally reswallowing. bypass the rumen and reticulum and pass
Regurgitation is the only step of rumi- through the omasum directly to the abo-
nation that differs markedly from the initial masum. The paunchiness of bucket‐fed