UNP-0060 Digestive System of Goats
Digestive System of Goats
Introduction
Mature goats are herbivorous ruminant animals. Their digestive
tracts, which are similar to those of cattle, sheep, deer, elk,
bison, and giraffes, consist of the mouth, esophagus, four stomach
compartments, small intestine, cecum, and large intestine. A brief
description of the anatomy and physiology of the mouth and the
stomach compartments of goats follows.
Mouth: Like other ruminant animals, goats have no upper
incisor or canine teeth. They depend on the rigid dental pad in
front of the hard palate, the lower incisor teeth, the lips, and
the tongue to take food into their mouths.
Esophagus: This is a tubelike passage from the mouth
to the stomach. The esophagus, which opens into the stomach at
the junction of the rumen and reticulum, helps transport both
gases and cud.
Rumen: This is the largest of the four stomach compartments
of ruminant animals. The capacity of the rumen of goats ranges
from 3 to 6 gallons depending on the type of feed. It is lined
with small fingerlike projections called papillae, which increase
the absorptive surface of the rumen. This compartment, also known
as the paunch, contains many microorganisms, such as bacteria
and protozoa, that supply enzymes to break down fiber and other
feed parts. Microbiological activities in the rumen result in
the conversion of the starch and fiber of feeds to the volatile
fatty acids acetic, propionic, and butyric acids. These volatile
fatty acids are absorbed through the rumen wall and provide as
much as 80 percent of the animal's total energy requirements.
Microbial digestion in the rumen is the reason that ruminant animals
effectively use fibrous feeds and are maintained primarily on
roughages.
Rumen microorganisms also convert components of the feed to
useful products such as essential amino acids, B-complex vitamins,
and vitamin K. Afterward, the micro-organisms themselves are digested
in the small intestine to free up these nutrients for the ruminant
animal's use.
In the process of digesting feeds, rumen microorganisms also
produce large amounts of gases, primarily methane and carbon dioxide.
The animal normally eliminates these gases by eructation (belching).
When the gases are produced faster than the animal can eliminate
them, a potentially lethal condition known as bloat can result.
This condition is often associated with the rapid consumption
of large amounts of leguminous vegetation.
The digestive tract of goats. |
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Reticulum: This compartment, also known as the honeycomb
or hardware stomach, is located just below the entrance of the
esophagus into the stomach. When goats swallow foreign objects
such as wire, nails, and screws, these objects can become lodged
in the reticulum, potentially causing serious injury. The reticulum
is part of the rumen separated only by an overflow connection,
the rumino-reticular fold. Therefore, microbial action also takes
place in this compart-ment. The capacity of the reticulum of goats
ranges from 1/4 to 1/2 gallon.
Omasum: This compartment, also known as the manyplies,
consists of many folds or layers of tissue that grind up feed
ingesta and squeeze some of the water from the feed. The capacity
of the omasum of goats is approximately 1/4 gallon.
Abomasum: This compartment is often considered the true
stomach of ruminant animals. It functions similarly to human stomachs.
The mucosa of the fundus contains parietal cells, which secrete
hydrochloric acid, and chief cells, which secrete the enzyme pepsin.
This enzyme is secreted in an inactive form (pepsinogen), which
is then activated by hydrochloric acid. Pepsin is responsible
for breaking down feed proteins before they enter the small intestine.
The pylorus, which is the terminal portion of the abomasum, is
characterized by secretions that are largely mucous. The capacity
of the abomasum of goats is approximately 1 gallon.
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Inside structures of rumen, reticulum, omasum,
and abomasum of goats. Photo courtesy of G. F. W. Haenlein, University
of Delaware. |
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Inside structures of rumen, reticulum, omasum, and abomasum
of deer.
Photo courtesy of G. F. W. Haenlein, University of Delaware. |
Small Intestine: As partially digested feed enters the
duodenum, the first part of the small intestine, the enzymes produced
and secreted by the pancreas and the Brunner's glands of the duodenum
further break down feed nutrients into simple compounds. These
compounds are absorbed into the bloodstream or lymph by an active
process carried on largely in the jejunum and ileum (second and
third part of the small intestine, respectively). The small intestinal
wall is lined with many small fingerlike projections called villi,
which increase the absorption area of the small intestine. The
capacity of the small intestine of goats is approximately 2-1/2
gallons.
Cecum: This simple tubular structure, also known as
the blind gut, is located at the junction of the small and large
intestines. Feed materials entering this compartment are digested
by inhabiting microorganisms. The capacity of the cecum of goats
is approximately 1/4 gallon.
Large Intestine: Undigested feed and unabsorbed nutrients
leaving the small intestine pass into this compartment. The functions
of the large intestine include water absorption and further digestion
of feed materials by microorganisms. The large intestine is comprised
of the colon and rectum. Fecal pellets are formed in the end portion
of the spiral colon. The capacity of the large intestine of goats
ranges from 1-1/4 to 1-1/2 gallons.
Accessory Glands: The salivary glands, liver, and pancreas
contribute to digestion. Saliva secreted by the salivary glands
is important in the chewing of the cud. Bile produced by the liver,
and stored and secreted by the gall bladder, helps emulsify fat
in preparation for digestion. Enzymes secreted by the pancreas
are important in the small intestinal digestion of carbohydrates,
proteins, and fats.
Development of the Four Stomach Compartments
When a goat kid is born, the rumen is small and the abomasum
is the largest of the four stomach compartments. The rumen of
a goat kid is about 30 percent of the total stomach area, while
the abomasum is about 70 percent. Hence, digestion in the goat
kid is like that of a monogastric animal. In the suckling goat
kid, closure of the esophageal groove ensures that milk is channeled
directly to the abomasum instead of going through the rumen, reticulum,
and omasum. Peptic cells in the abomasum of young milk-fed ruminants
secrete, in addition to pepsin, the enzyme rennin. This enzyme
is responsible for forming milk curdles and digesting milk protein.
When the suckling goat kid starts to eat vegetation during
the first or second week after birth, the rumen, reticulum, and
omasum gradually develop in size and function. After approximately
two months, the four stomach compartments reach their relative
adult proportions.
Rumination
Rumination is defined as the regurgitation, rechewing, and
reswallowing of rumen ingesta. During resting, animals with four
stomach compartments regurgitate ball-like masses of fibrous and
coarse feeds called bolus or the cud. The regurgitated cud is
chewed thoroughly for about one minute then swallowed again. Ruminant
animals may spend up to 8 hours per day in rumination, depending
on the type of feed. This phenomenon affects the amount of feed
the goat can eat. Reducing the particle size of the feed through
rechewing allows the material to be easily accessible to the microorganisms
and to pass out of the rumen.
Summary
Digestion in ruminant animals is accomplished via microbial
breakdown of feed parts in the rumen and reticulum, enzymatic
activity in the abomasum and small intestine, and microbial breakdown
in the cecum and large intestine. The simple compounds derived
from the digestion of carbohydrates, proteins, and fats are absorbed
mainly from the forestomach and small intestine.
References
Church, D. C. (1993). The ruminant animal: Digestive physiology and nutrition. Prospect Heights, IL:
Waveland Press, Inc.
Ensminger, M. E. (2002). Sheep and goat science. 6th ed. Danville, IL: Interstate Publishers, Inc.
Gillespie, J. R. (1998). Animal science. Albany, NY: Delmar Publishers.
Jurgens, M. H. (1993). Animal feeding and nutrition. 7th ed. Dubuque, IA: Kendall/Hunt Publishing Company.
Randall, D., Burggren, W., & French, K. (2002). Eckert animal physiology: Mechanisms and adaptations.
5th ed. New York, NY: W.H. Freeman and Company.
Shapiro, L. S. (2001). Introduction to animal science. Upper Saddle River, NJ: Prentice-Hall, Inc.
Taylor, R. E. and T. G. Field. (2001). Scientific farm animal production: An introduction to animal science.
7th ed. Upper Saddle River, NJ: Prentice-Hall, Inc.
Special thanks to Jean Hall Dwyer, Extension Communications Specialist, for the drawing "The digestive tract of goats."
Julio E. Correa, Extension Animal Scientist, Associate Professor, Food and Animal Sciences,
Alabama A&M University
For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.
Issued in furtherance of Cooperative Extension work in agriculture and
home economics, Acts of May 8 and June 30, 1914, and other related
acts, in cooperation with the U.S. Department of Agriculture. The Alabama
Cooperative Extension System (Alabama A&M University and Auburn
University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color,
national origin, religion, sex, age, veteran status, or disability.
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