Page 414 - Anatomy and Physiology of Farm Animals, 8th Edition

Physiology of Digestion / 399

(A)
Distention
VetBooks.ir

Bolus Intestine

(B)

Oral Aboral

Contraction Relaxation
(C)

(D)

Figure 21-2. Intestinal peristalsis and movement of contents. (A) Original distension. (B) Contraction
cranial to distension and relaxation caudal. (C) Movement of contents. (D) New distension point and new
points of contraction and relaxation. Source: Reece, 2009. Reproduced with permission of John Wiley &
Sons, Inc.

The microbial digestion in the forestom- particularly difficult if foam forms. The
ach occurs in an anaerobic environment and buildup of gas results in enlargement of
is termed fermentative digestion. Volatile the rumen and reticulum, which in turn
fatty acids (VFAs) are produced by fermen- press on the thorax, inhibiting function
tation of carbohydrates consumed by rumi- of the heart and lungs. A stomach tube
nants, including carbohydrates produced by may be passed into the rumen by mouth
the actions of microbial cellulase. The pri- to remove the gas. If that is not possi-
mary VFAs are acetic acid, propionic acid, ble, a trocar (sharp tube) may be passed
and butyric acid. The VFAs are absorbed into the rumen through the left flank.
directly from the forestomach and are the Dietary protein consumed by ruminants
major energy source for ruminants. VFAs is available first to the microbes in the
are also used for synthesis of milk fat in forestomach. The microbes may use the
lactating ruminants. dietary protein to produce microbial pro-
Methane and carbon dioxide are pro- teins and promote microbial growth or to
duced by fermentative digestion and produce VFAs by fermentative digestion.
accumulate as a gaseous layer above the Microbes can also produce microbial pro-
ingesta in the rumen and reticulum. Bloat teins from nonprotein nitrogen sources,
(acute tympany) results from more gas such as urea and ammonia.
being produced than is eliminated by The microbes and by‐products of micro-
eructation (belching). Eructation is bial metabolism other than VFAs continue