Download Anatomy - Digestion - Clackamas Career and Technical Education

Lesson Plan Template Instructor: Kate Dean Date: June 25, 2013 Course Title: Animal Science Specific Topic: Comparative Anatomy ‐ Digestion Reading Assignment: Domestic Animal Digestive Tract Anatomy Article
Performance Objectives: After completion of the lesson, students will be able to:
1. Describe the differences between a monogastric, ruminant, avian and cecal fermenter digestive tract 2. Describe how different animals have evolved to best digest certain food stuffs 3. Identify the location of symbiotic microbes in the guts of domestic animals ANS 02.02.
Apply principles of comparative anatomy
and physiology to uses within various
animal systems.
9‐10.RST.1 Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions. Standards: CTE & CCSS Assessment: 9‐10.SL.1 Initiate and participate effectively in a range of collaborative discussions (one‐
on‐one, in groups, and teacher‐led) with diverse partners on grades 9 10 topics, texts, and issues, building on others’ ideas and expressing their own clearly and persuasively 9‐10.WHST.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/ experiments, or technical processes. Completion of Four square Perspective Chart Materials: Copies of 4 digestive tract articles Copies of Digestive tract note chart and four square perspective chart Procedure: Literacy Strategy used: Cloverleaf technique Four square perspective chart Introduction and Method of activating prior knowledge – ‐
‐
As a way to review material from the previous lesson, students will first fill out a diagram of a basic digestive tract – labeling the following: esophagus, stomach, liver, pancreas, duodenum, jejunum, ileum, cecum/appendix, large intestine, rectum, anus The class will go over the correct labels and review the basic function of each organ Individual: Students will take one of the articles and use the digestive tract note chart to record the important points from the article – they will be given 10 minutes to complete this task Group: Groups of 4 – one student with each of the articles will group together. The teacher will identify which article will go first – the student who read that article will describe the important information to the other members of the group. Other members of the group will record the information, asking clarifying questions to ensure they have the material they need for the culminating task. The teacher will allow 5‐10 minutes for each of the article presentations – groups will wait for others to finish before moving to the next article presentation. Entire Class: Students will use their completed notes chart to individually fill in the four square perspective organizer – this will be handed in at the end of the period and used as an informal assessment to determine if the group is on the right track. Application of Material: Extension Questions: Accommodat ions needed: Species of Animal Pig Cow Chicken Horse What do you already know about how this animal digests? Type of food this animal is built to digest Specialized structures found in the tract Location of symbiotic bacteria in tract Four-Square Perspective
publication 400-010
Nutrition and Feeding of the Cow-Calf Herd:
Digestive System of the Cow
John B. Hall, Extension Animal Scientist, Virginia Tech
Susan Silver, Graduate Teaching Assistant, Virginia Tech
Proper nutrition is the foundation for a productive and
profitable cow-calf herd. Without good nutrition, cattle
cannot express their full genetic potential nor will they
be reproductively efficient. Often low reproductive
rates, poor growth, and increased illness are a result of a
nutritional imbalance or deficiency rather than a disease
or genetics. In addition, pasture and feed represent the
single largest cost associated with the cowherd.
Cow-calf producers need to understand basic digestive physiology, types of nutrients, and requirements of
the cow in order to be competent on-farm nutritionists.
By understanding feeds and ration balancing, producers can meet the nutritional needs of their animals in a
more cost efficient manner. In addition, a fundamental
understanding of feeds and rations will assist producers in evaluating new products, alternative feeds, and
supplements. The Nutrition and Feeding of the CowCalf Herd series provides the information necessary to
become a better nutritional manager.
Cattle Have A Unique Digestive
System
Mouth and Teeth
Cattle belong to a class of animals known as ruminants.
Ruminants are cloven hooved animals that have four
compartments to their stomach and chew their cud. In
addition, ruminants have an unusual configuration of
teeth. Their small and large intestine are designed to
handle large volumes of material. Cattle evolved to
exist on large amounts of fiber. They do not do well on
all grain or high fat diets.
The mouths of cattle are very different from most nonruminant animals (Figure 1). Cattle have 32 teeth. They
have 6 incisors and 2 canines in the front on the bot-
Figure 1. Tooth & jaw structure of cattle.
Proper nutrition is essential for good reproduction.
www.ext.vt.edu
Produced by Communications and Marketing, College of Agriculture and Life Sciences,
Virginia Polytechnic Institute and State University, 2009
Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion,
age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University,
and the U.S. Department of Agriculture cooperating. Rick D. Rudd, Interim Director, Virginia Cooperative Extension, Virginia
Tech, Blacksburg; Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg.
tom. The canines are not pointed but look like incisors.
There are no incisors on the top; instead cattle have a
dental pad. Cattle have 6 premolars and 6 molars on
both top and bottom jaws for a total of 24 molars. In
addition, there is a large gap between the incisors and
molars. This configuration allows cattle to harvest and
chew a large amount of fibrous feed.
The bacteria and protozoa do most of the digestion of
feeds for the cow. This is a tremendous factory. There
are 25 to 50 billion bacteria and 200 to 500 thousand
protozoa in every milliliter of rumen fluid (about 0.06
ounces). The microorganisms digest the plant fiber
and produce volatile fatty acids. These fatty acids are
absorbed directly through the rumen wall and supply 60
to 80 % of the energy needed by the cow. In addition to
energy, the microorganisms produce protein including
essential amino acids from the protein and nitrogen the
cow ingests. Because the microbes can use nitrogen
to make protein, cows can eat urea and other sources
of non-protein nitrogen that would kill non-ruminants.
The microbes also make vitamins B and C.
Because their teeth are primarily for grinding, cattle use
their tongues to grasp or gather grass and then pinch it
off between their incisors and dental pad. Since they
lack upper incisors, cattle cannot bite off grass very well,
and they are inefficient at grazing closely. The inside of
the cheeks and palate are rough which helps hold feed in
while cattle chew with a side to side motion.
The reticulum, with its honeycomb like lining, is a
compartment of the stomach that is involved with rumination. It also acts as a trap for foreign objects ingested
by the cow. It is not unusual to find rocks, nails, and
pieces of wire and metal in the reticulum of cattle. If
wire or metal punctures the side of the reticulum, it can
cause “hardware disease.” Hardware disease is actually an irritation or infection of the diaphragm, heart
or lungs. It is hard to treat, but can be prevented by
keeping metal trash out of pastures. Specially shaped
magnets can be administered to cows to decrease the
possibility that ingested metal will pierce the digestive
tract. These magnets stay in the reticulum for the life
of the animal.
In addition to reducing the size of feed particles, the
mouth aids in digestion by adding saliva to the feed.
Cows will produce 20-35 gallons of saliva a day. The
saliva helps moisten the feed. Saliva also contains
sodium bicarbonate to keep the rumen at the proper
neutral pH (6.5-7.2) for good microbial growth. Much
of the water contained in saliva is recycled by the cow.
Stomach
The four compartments of the cattle stomach are the
rumen, reticulum, omasum, and abomasum (Figure 2).
The rumen is the largest compartment, and it contains
billions of bacteria, protozoa, molds, and yeasts. These
microorganisms live in a symbiotic manner with the
cow, and they are the reason cattle can eat and digest
large amounts of roughage. The rumen microorganisms are adaptable enough that cattle can digest a large
variety of feeds from grass, hay, and corn to brewer’s
grains, corn stalks, silage, and even urea.
When cattle ruminate, or chew their cud, they are regurgitating a bolus of incompletely chewed feed. In order
for the microbes to digest fiber rapidly and efficiently it
must be in small pieces, so cattle re-chew their food several times. Cows also eructate or belch giving off carbon
dioxide and methane. When cows “lose their cud” or
stop ruminating, it is an indication that they have a digestive upset, and their rumen is not functioning properly.
Bloat is another condition that occurs when cows can’t
eructate. It is caused by a rapid change in feed or overeating grain (gaseous bloat) or grazing pure stands
of clover or alfalfa (frothy bloat). Gaseous bloat is a
result of improper digestion or fermentation of grain.
It is treated by passing a tube into the rumen or using a
trocar and cannula to make an external opening in the
rumen to release the gas pressure. The procedure may
have to be repeated. Frothy bloat is a result of surfactants in legumes causing gas to be trapped in a bubbly
foam. Large amounts of mineral oil must be forced into
the rumen via a tube to break up the bubbles as a treatment for frothy bloat. Bloat must be treated quickly as
Figure 2. Compartments of the stomach of cattle.
2
the increased rumen size and pressure interferes with
normal breathing.
the lower digestive tract includes some microbes and
undigested fiber, as well as protein and some sugars
produced by the microbes. By-pass protein, fat, and
carbohydrates also enter the lower digestive tract. Bypass protein, fat, and carbohydrates are nutrients that
cannot be digested in the rumen but may be digested in
the abomasum and small intestine.
The incidence of bloat in cattle grazing legumes can
be reduced by maintaining at least 50% of the stand as
grass. Also, cattle should not be turned out onto a pasture with a high percentage of legumes when cattle are
hungry or the pasture is wet. Once cattle are adapted
to legume/grass pastures, they can graze it even when
wet. A final option is to use “bloat guard” blocks which
contain poloxolene.
Enzymes to digest proteins, sugars, and starch flow into
the small intestine from the pancreas, while the gall
bladder produces bile to help digest fats. The small
intestine also produces some enzymes to aid in digestion, but its major function is absorption of digested
nutrients. Except for the volatile fatty acids, most of
the nutrients are absorbed in the small intestine including protein, starch, fats, minerals and vitamins.
Although rumen microbes can digest a great variety of
different feeds, they are very sensitive to drastic changes
in feeds. Some groups of microbes are better at digesting fiber (forages), whereas others are better at digesting
starch (grains). Changing rapidly from a forage-based
diet to a grain-based diet causes millions of fiber-digesting microbes to die-off as they cannot digest the
starch, and there are too few starch-digesting microbes
to use the grain so the grain sours in the rumen. As a
result, rumen pH decreases, the rumen stops working,
and the animal becomes ill. In severe cases, cattle can
develop acidosis and founder or die.
Water is primarily absorbed in the large intestine.
Undigested feed, some excess water, and some metabolic wastes leave the large intestine as fecal material.
The consistency of manure is an indicator of animal
health and is dependent on water, fiber, and protein content of the feed. For example, cattle on lush spring forage will have profuse watery, greenish colored manure,
whereas animals on a hay diet will have firm manure
that is dark in color. Animals should produce manure
that is indicative of the diet they are receiving. If not, it
may indicate a digestive upset or disease. Light colored
manure, manure tinged with blood, and watery manure
(when on a dry diet) are not normal situations. Manure
should not smell putrid or rancid. Producers should
recognize changes in manure that indicate problems.
The omasum is also known as “the book” or many
piles because of its many leaf-like folds. It functions as
the gateway to the abomasum, filtering large particles
back to the reticulorumen and allowing fine particles
and fluid to be passed to the abomasum. Though the
complete function of this compartment is unknown, it
does aid in water resorption and recycling of buffers for
the saliva. The omasum may also absorb some volatile
fatty acids.
The abomasum is also known as the “true stomach.” It
functions much like the human stomach producing acid
and some enzymes to start protein digestion. Animals
that go off feed or have acidosis can develop a displaced
abomasum or “twisted stomach.” The abomasum will
actually float out of place and become torsioned stopping the flow of digesta. Surgery is the only cure for a
displaced abomasum. Although displaced abomasum
is more common in dairy cattle than beef cattle, producers should be aware of the possibility of this problem in
cattle that have had severe digestive upsets.
Lower Digestive Tract
The rest of digestion is performed in the small intestine
and large intestine much as it is in humans and other
mammals. Digesta that leaves the rumen and enters
Grazing should provide a majority of nutrients.
3
Feeding Management
Healthy rumen = healthy cattle
Although proper nutrition and cattle health goes beyond
taking care of the rumen microbes, reducing digestive problems and promoting a rumen with a healthy
microbe population can prevent many serious problems
in cattle. The following are some rules for maintaining
rumen health:
• P
rovide a diet that meets the energy, protein and mineral requirements of the animal.
• Make sure water is clean and available.
• P
ay attention to fiber levels in diets; a fiber level
between 30% and 70% is preferred.
• S
witch from high fiber diets to high grain diets slowly;
change should occur gradually over days or weeks.
• Diets should contain 5% or less fat.
• C
hanging from a high grain diet to a high fiber diet
will generally NOT cause digestive upsets, but will
reduce performance.
• D
o not move hungry or newly received cattle into
pastures containing a high percentage (>25%) of
legumes.
• D
o not introduce cattle to high percentage legume
pastures when pastures are wet.
• S
upply cattle grazing pasture containing >50%
legumes with ionophores or poloxolene.
• M
onitor rumination and fecal output to aid in early
detection of digestive problems.
References
Church, D.E. 1984. Livestock Feeds and Feeding. Corvallis: O&B Books.
Ensminger and Olentine. Feeds and Feeding. Clovis:
Ensminger Publishing Company.
Sisson and Grossman. The Anatomy of the Domestic
Animals.
Reviewed by Scott Greiner, Extension specialist, Animal and Poultry Sciences
4
AS23
The Digestive Tract of the Pig1
J.P. Rowan, K.L. Durrance, G.E. Combs and L.Z. Fisher2
The pig has a digestive system which is classified as
monogastric or nonruminant. Humans also have this type
of digestive system. They have one stomach (mono=one,
gastric=stomach). The monogastric differs from that of a
polygastric or ruminant digestive system found in cattle
and sheep. These animals have one stomach broken into
four compartments. Due to the differences in the digestive
systems, cattle can utilize different types of feeds than pigs.
Cattle and sheep can live on hay and pasture, while pigs
must eat grains that can be digested more easily.
Digestion is the break-down of food occurring along the
digestive tract. The digestive tract may be thought of as
a long tube through which food passes. As food passes
through the digestive tract, it is broken down into smaller
and smaller units. These small units of food are absorbed as
nutrients or pass out of the body as urine and feces.
Figure 1.
The mouth is where food enters the digestive tract and
where mechanical breakdown of food begins ( Figure 2 ).
The teeth chew and grind food into smaller pieces. Saliva
, produced in the mouth, acts to soften and moisten the
small food particles. Saliva also contains an enzyme which
The digestive tract of the pig has five main parts: the mouth,
esophagus, stomach, and small and large intestines ( Figure
1 ). The following discussion explains how each part digests
nutrients.
Figure 2.
1. This document is AS23, one of a series of the Animal Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural
Sciences, University of Florida. Original publication date March 1997. Revised June 2003. Reviewed by R. Myer, October 2011. Visit the EDIS website at
http://edis.ifas.ufl.edu.
2. J.P. Rowan is an Extension Agent - Agriculture, 4-H, Suwannee County; K.L. Durrance is Professor, Animal Sciences Department; G.E. Combs is Professor,
Animal Sciences Department, and L.Z. Fisher is Visiting Extension Agent, 4-H Department, Cooperative Extension Service, Institute of Food and
Agricultural Sciences, University of Florida, Gainesville, 32611. Reviewed by Joel Brendemuhl and Robert O. Myer, December, 1996.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to
individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national
origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative
Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean
starts the digestion of starch. The tongue helps by pushing
the food toward the esophagus.
The esophagus is a tube which carries the food from the
mouth to the stomach. A series of muscle contractions
push the food toward the stomach. Swallowing is the first
of these contractions. At the end of the esophagus is the
cardiac valve, which prevents food from passing from the
stomach back into the esophagus.
The stomach is the next part of the digestive tract ( Figure
3 ). It is a reaction chamber where chemicals are added
to the food. Certain cells along the stomach wall secrete
hydrochloric acid and enzymes. These chemicals help break
down food into small particles of carbohydrates , protein
, and fats . Some particles are absorbed from the stomach
into the bloodstream. Other particles which the stomach
cannot absorb pass on to the small intestine through the
pyloric valve.
At the first section of the small intestine (called the duodenum ) secretions from the liver and pancreas are added.
Secretions from the liver are stored in the gall bladder and
pass into the intestine through the bile duct. These bile
secretions aid in the digestion of fats.
Digestive juices from the pancreas pass through the
pancreatic duct into the small intestine. These secretions
contain enzymes that are vital to the digestion of fats,
carbohydrates, and proteins.
Most food nutrients are absorbed in the second and third
parts of the small intestine, called the jejunum and the
ileum . Undigested nutrients and secretions pass on to the
large intestine through the ileocecal valve.
A “blind gut” or cecum is located at the beginning of the
large intestine ( Figure 5 ). In most animals, the cecum
has little function. However, in animals such as the horse
and rabbit, the cecum is very important in the digestion of
fibrous feeds.
Figure 3.
The small intestine is a complex tube which lies in a spiral,
allowing it to fit in a small space ( Figure 4 ). Its wall has
many tiny finger-like projections known as villi , which
increase the absorptive area of the intestine. The cells along
the small intestine’s wall produce enzymes that aid digestion and absorb digested foods.
Figure 5.
The last major part of the digestive tract, the large intestine,
is shorter, but larger in diameter than the small intestine. Its
main function is the absorption of water. The large intestine
is a reservoir for waste materials that make up the feces.
Some digestion takes place in the large intestine. Mucous
is added to the remaining food in the large intestine,
which acts as a lubricant to make passage easier. Muscle
contractions push food through the intestines. The terminal
portion of the large intestine is called the rectum.
The anus is an opening through which undigested food
passes out of the body. Food that enters the mouth and is
not digested or absorbed as it passes down the digestive
tract is excreted through the anus as feces.
Figure 4.
This was a general discussion of the digestive tract of the
pig. The tract acts to digest and absorb nutrients necessary
2
for maintenance of cells and growth. Efficient absorption of
nutrients depends on each segment of the digestive system
functioning to its maximum capacity.
Figure 6 gives a summary of the digestive system of the
pig. You may wish to test your knowledge by identifying the
parts in Figure 7.
7. Duodenum - the first section of the small intestine
8. Enzymes - substances that speed up chemical reactions
within the body
9. Esophagus - a tube which carries food from the mouth
to the stomach
lO. Fats - energy nutrients which supply 2.25 times as
much energy as carbohydrates.
11. Gall Bladder - a sac-like structure which serves as a
storage compartment for bile
12. Ileocecal Valve - the valve separating the ileum and the
cecum
13. Ileum - the terminal portion of the small intestine
Figure 6.
References are listed at the end of this publication. You can
get additional information by referring to a farm animal
anatomy book.
References
1. Advanced Livestock Science Manual, University of
Illinois at Urbana, Champaign Cooperative Extension
Service.
14. Jejunum - the intermediate or middle portion of the
small intestine
15. Liver - a gland in the body which performs a number of
functions including the secretion of bile
16. Monogastric - having only one stomach
(non-ruminant)
17. Pancreas - a gland which secretes digestive juices necessary for the digestion of fats, carbohydrates, and proteins.
2. Swine Technology, Farm Science Services, Extension
Bulletin 536, January, 1975 (Rev’d), Cooperative Extension
Service, Michigan State University.
18. Pancreatic Duct - a duct which carries secretions of the
pancreas to the small intestine
Glossary
19. Polygastric - having more than one stomach
(ruminants)
1. Anus - the last part of the digestive tract through which
undigested food passes out of the body
2. Bile - a secretion of the liver which aids in the digestion
of fats
3. Bile Duct - a duct which carries bile from the gall
bladder to the small intestine
4. Cardiac Valve - a valve which prevents food from
passing from the stomach back up into the esophagus
5. Carbohydrates - the main nutrients which supply
energy to the body (starch and cellulose)
2O. Pyloric Valve - the valve separating the stomach and
the small intestine
21. Proteins - the nutrients which supply the building
materials from which body tissue and many body regulators are made
22. Rectum - the terminal portion of the large intestine
23. Saliva - an enzyme secreted from the mouth which
begins carbohydrate digestion
24. Villi - tiny finger-like projections located along the wall
of the small intestine which aid in food absorption
6. Cecum - a “blind gut” located between the ileum and the
large intestine
3
4
Figure 7. Test your knowledge by identifying the parts.
AFS-
Avian digestive system
Jacquie Jacob, Tony Pescatore and Austin Cantor
An understanding of the avian digestive system is essential to developing an effective and
economical feeding program for your poultry
flock. A knowledge of chicken anatomy, and
what the parts normally look like, will also help
you to recognize when something is wrong and
take the necessary actions to correct the problem.
The digestive tract of any animal, including
chickens, is important in converting the food
the animal eats into the nutrients their body
Figure 1. Model showing the internal organs of the female chicken
ends at the cloaca and has several important
organs in between (see the Figure 2 below).
needs for maintenance, growth, and production (such as eggs). Once food is eaten, it
must be broken down into its basic components. This is done through both mechanical
and chemical means.
Beak / Mouth: Chickens, as with most birds,
obtain feed with the use of their beak. Food
picked up by the beak enters the mouth. As
previously mentioned, chickens do not have
teeth so they are not able to chew their food.
The mouth does contain glands which secrete
saliva which wets the feed to make it easier to
swallow. The saliva also contains some enzymes which start the digestion of the food
eaten. The chicken’s tongue is then used to
push the feed to the back of the mouth so that
it can be swallowed.
 Mechanical
action typically involves
chewing, but since birds don’t have teeth
other mechanical methods are used and
will be discussed later in this publication.
 Chemical action includes the release of
digestive enzymes and fluids from the
stomach, pancreas and liver.
Once the nutrients have been released from
food during digestion, they can be absorbed
and distributed throughout the animal’s body.
Esophagus: The esophagus is a flexible tube
that connects the mouth with the rest of the
digestive tract. It carries food from the mouth
to the crop and from the crop to the proventriculus.
The digestive tract is also referred to as the
gastro-intestinal or GI tract. Which ever term is
used, in chickens it begins at the mouth and
Figure 2. Labeled photograph of the digestive tract of a chicken
2
Did you know: Chickens swallow water differently than we do. While they use their
tongue to push food to the back of the throat this is not very effective when swallowing water. We close our mouths and let our throats do the swallowing. Chickens,
however open and close their mouths rapidly while tilting their heads up, since they
Crop: The crop is an out-pocketing of the
esophagus and is located just outside the body
cavity in the neck region (see Figure 3 below).
Any swallowed feed and water is stored in the
crop until it is time to pass it on to the rest of
the digestive tract. When the crop is empty, or
nearly empty, it sends hunger signals to the
brain so that the chicken will eat more.
Figure 3. Location of the crop in a chicken.
The crop is located just outside the body cavity in the neck region.
Although salivary glands of the mouth secrete
the digestive enzyme amylase very little digestion actually takes place in the crop – it is
simply a temporary storage pouch. The crop
evolved for birds that are typically hunted by
other animals but which need to move to the
open to find feed. These birds are able to consume relatively large amounts of food quickly
and then move to a more secure location to
digest the food they consumed.
Figure 4. Front and back views of the proventriculus and gizzard
Occasionally the crop becomes impacted or
’backed up’ (crop impaction, also referred to
as crop binding or pendulous crop). This
may occur when chickens go a long time without feed. This will cause the chickens to eat
too much too fast when the feed becomes
available again. A crop may also become impacted in a chicken that is free-ranged on a
pasture of tough, fibrous vegetation. Crop impaction can also result when the chickens eat
a long piece of string. With a crop impaction,
even if a chicken continues to eat, the feed can
not get past the impacted crop. The swollen
crop may also cut off the windpipe, suffocating
the chicken.
Proventriculus
Proventriculus
Gizzard
Gizzard
ever, the food has not yet been ground up. The
term ‘proventriculus’ is used since it comes before the ‘ventriculus’ or gizzard, with ‘pro’ being
a Latin terming meaning before.
Gizzard / Ventriculus: The gizzard, or ventriculus, is a part of the digestive tract unique
to birds. It is often referred to as the
‘mechanical stomach’. It is made up of two
sets of strong muscles which act as the bird’s
teeth (see Figure 4 above). Consumed feed
and the digestive juices from the salivary
glands and the proventriculus pass into the
gizzard for grinding, mixing, and mashing.
Proventriculus: The esophagus continues
past the crop to connect the crop to the
proventriculus. The proventriculus (also known
as the ‘true stomach’) is the glandular stomach where digestion begins. As with human
stomachs, hydrochloric acid and digestive enzymes (e.g., pepsin) are added to the feed
here and digestion begins. At this point, how-
When allowed to free-range, chickens will typically eat small stones. These stones remain in
the gizzard until they become ground into
3
Warning: Do NOT give chicks oyster shell or limestone. These are NOT grit. Oyster shell
and/or limestone are often given to laying hens to provide the extra calcium they need for
egg shell formation. This extra calcium, however, will cause bone development problems in
chicks. The kidneys can be damaged as well.
pieces small enough to pass through to the
rest of the digestive tract. The stones/pebbles
are weakened by the acidic environment created in the proventriculus and then are ground
into tiny pieces by the strong muscles of the
gizzard.
grinding motion of the gizzard’s muscles, these
sharp objects may eventually put a hole in the
gizzard wall. Chickens with damaged gizzards
will grow thin and eventually die – a very good
reason to keep your poultry houses free of
nails, glass shards, bits of wire and the like.
Chickens fed only commercially prepared feed
do not need stones. If, however, whole grains
are fed, it is necessary to provide small pebbles, typically given as grit. Grit is a commercial product made up of small stones. It should
not be confused with limestone or oyster shell
which are given to laying hens as a source of
calcium for their egg shells.
Small intestine: The small intestine is made
up of the duodenum (also referred to as the
duodenal loop) and the lower small intestine.
The duodenum receives digestive enzymes
and bicarbonate (to counter the hydrochloric
acid from the proventriculus) from the pancreas and bile from the liver via the gall bladder. The digestive enzymes produced by the
pancreas are primarily involved in protein digestion. Bile is a detergent that is important in
the digestion of lipids and absorption of fatsoluble vitamins (vitamins A, D, E and K). The
remainder of the digestion occurs in the duodenum and the released nutrients are absorbed mainly in the lower small intestine.
The lower small intestine is composed of two
parts, the jejunum and ileum. The Merkel’s Diverticulum marks the end of the jejunum and
the start of the ileum.
Chickens kept on pasture will also require supplementation with grit, though many of them
may consume enough pebbles when they forage.
Gizzards have a thick lining which protects
their muscles (see Figures 5 and 6 below).
When chickens are slaughtered, the gizzards
are often saved, the lining removed, and the
gizzard consumed by the family or sold as a
food item. While many people use chicken gizzards in home-made pet food (typically dogs
and cats) they can also be a human food item,
eaten alone or as part of a recipe.
The pancreas plays important roles in both
the digestive and hormonal systems. It secretes hormones into the blood system that
are important in the regulation of blood sugar.
When a chicken eats a small, sharp object
such as a tack or staple, the object is likely to
get stuck in the gizzard. Because of the strong
Figure 5. The inside of
the proventriculus and
gizzard.
In the developing embryo the yolk sac supplies
the nutrients needed for it to develop and
grow. Right before hatch, the yolk sac is taken
into the navel cavity of the embryo. The residual tiny sac is the Merkel’s Diverticulum (see
Figure 6. The inside of
the gizzard with the
inner lining removed.
Figure 7. The positioning of the
Merkel’s Diverticulum between the jejunum and ileum portions of the small in4
Jejunum
Ileum
Merkel’s
Diverticulum
Figure 7 below).
absorption occurs.
The material remaining in the yolk immediately
after hatch is able to supply the feed and water
needs of the newly hatched chicken. This is
why it is possible to ship chicks long distances
without adverse affects, as is done when
chicks are purchased online and shipped via
the postal service.
Cloaca: In the cloaca there is a mixing of the
digestive wastes together with wastes from the
urinary system (urates). Fecal material is usually voided as digestive waste with white uric
acid crystals on the outer surface (i.e., chickens do not urinate/pee). The reproductive tract
also exits through this area but when a hen
lays an egg the vagina folds over to allow the
egg to leave through the vent without coming
into contact with the feces or urine.
Omphalitis is a condition characterized by infected yolk sacs, often accompanied by unhealed navels in recently hatched chicks. It is
infectious but not contagious. It is often associated with excessive humidity and contamination of the hatching eggs or incubator. The affected chicks usually appear normal until a few
hours before death. Being lethargic, drooping
of the head, and huddling near the heat source
usually are the only signs. The navel may be
inflamed and fail to close, producing a wet spot
on the abdomen; a scab may be present.
The color and texture of chicken fecal material
can indicate the health status of the chicken’s
digestive tract. The white pasty material that
commonly coats chicken fecal material is uric
acid, the avian form of urine, and is normal
(see Figure 8 below).
Ceca (plural form; singular = cecum): The
ceca are two blind pouches located where the
small and large intestines join. Some of the
water remaining in the fecal material is reabsorbed here. Another important function of the
ceca is the fermentation of any remaining
coarse materials. In doing so they produce
several fatty acids as well as the eight B vitamins (Thiamine, riboflavin, niacin, pantothenic
acid, pyridoxine, biotin, folic acid and vitamin
B12). Because the ceca are located so close to
the end of the digestive tract, however, very
little of the produced nutrients are absorbed
and available to the chicken.
Some of the possible abnormal color and texture changes that can occur, together with
possible causes, are shown below. These are
just possible causes—any sick birds should be
diagnosed by a veterinarian.
Figure 8. ‘Normal’
chicken fecal material
show the dark fecal
material with a coating of white uric acid
crystals
Appearance of Feces
Droppings with blood = coccidiosis
Greenish droppings = late stages of worms
(or has eaten a lot of green vegetables if
free-ranged)
White, milky runny droppings = worms, coccidiosis, Gumboro disease (Infectious
Bursal Disease)
Brown runny droppings = E. coli infection
Clear or watery runny droppings = stress,
Infectious Bronchitis
Yellow & foamy droppings = coccidiosis
Grayish white & running continuously = vent
gleet (a chronic disease of the cloaca of
domestic birds)
The ceca empty their contents two or three
times a day, producing pasty droppings that
often smell worse than regular droppings. Cecal droppings typically have a mustard to dark
brown in color. The number of times cecal
droppings are ‘pooped’, as well as their color
and texture, tell you that the chicken’s digestive tract is functionally normally.
Large intestine (also known as the colon):
Despite the name, the large intestine is actually shorter than the small intestine. The large
intestine is where the last of the water re5
Intestinal Microflora
‘enteritis’ refers to an inflammation of the intestinal tract. Necrotic enteritis is a problem in
many different types of production systems.
Both the small and large intestine are normally
populated by beneficial bacteria, referred to as
microflora (‘micro’ meaning small and ‘flora’
meaning plants). This population of microflora
are important since they aid in digestion. Intestinal disease normally occurs when the balance of normal microflora is upset or the normal microflora is overrun by too many foreign
organisms. The result is enteritis or inflammation of the intestines, producing symptoms that
include diarrhea, increased thirst, dehydration,
loss of appetite, weakness, and weight loss or
slow growth.
So where do these ‘beneficial’ bacteria come
from? When chicks hatch their digestive tracts
are virtually sterile. If raised by a mother hen,
they would obtain the beneficial microflora by
consuming some of their mother’s fecal material. This is not possible in artificial incubation
and brooding. Probiotics are a collection of the
normal beneficial microflora that would inhabit
a chicken’s digestive tract. By spraying it in the
shipping boxes or supplying it in the first feed
the chicks receive the ’good’ bacteria that they
need to fight off infection by pathogenic bacteria, such as salmonella.
When the damage to the intestinal tract is severe it is typically referred to as necrotic enteritis. ‘Necrotic’ means ‘dead tissue’ while
Educational programs of Kentucky Cooperative Extension serve all people regardless of race, color, age, sex, religion, disability, or national origin. Issued in furtherance of Cooperative Extension
work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, M. Scott Smith, Director, Land Grant Programs, University of Kentucky College of Agriculture, Lexington, and Kentucky State University, Frankfort. Copyright 2011 for materials developed by University of Kentucky Cooperative Extension. This publication may be reproduced in portions or its entirety
for educational and nonprofit purposes only. Permitted users shall give credit to the author(s) and include this copyright notice. Publications are also available on the World Wide Web at
www.ca.uky.edu.
Issued 02-2011
6
Overview of Digestion in Horse:
How does the horse digest feed and therefore make use of the nutrients contained within the feedstuffs it
consumes? This question is of fundamental importance to equine nutritionists, and while it is not necessary for
you to become bogged down in the intricacies of equine digestive physiology, a basic understanding of how
the horse digests feed is necessary for the selection of appropriate diets and feeding practices.
At the outset, it is useful to remind ourselves that horses evolved as forage eaters, grazing for upwards of 16
to 17 hours each day and traveling considerable distances as they graze. The horse’s digestive system is well
suited to this feeding behavior – the stomach and small intestine are designed to cope with the almost
continual entry of small amounts of food while the large intestine is geared toward the extraction of maximum
nutritional value from the fibrous feeds. Now consider how the pressures of domestication have dictated
changes in diet and feeding behavior: Continual access to pasture is but a dream for most horses, and many
spend a considerable part of the day in a stall. As well, our own schedules dictate feeding programs – rather
then continual grazing, horses are often fed large meals morning and night. The high-energy requirements of
the performance horse have necessitated inclusion of more energy-dense ingredients such as cereal grains and
fat in horse diets. All of these factors can contribute to digestive upsets, some of which can be avoided by
returning the horse to a more “natural” feeding circumstance.
Twists and Turns
The basic components of the digestive tract are similar in all mammals – the mouth (including salivary
glands), esophagus, stomach, small intestine, cecum and large colon. We can divide the horse’s digestive
system into two sections. The pre-cal section (esophagus, stomach and small intestine) function much as in
man, dog and pig. On the other hand, the cecum and large intestine work like the forestomachs of a ruminant
(e.g. cow or sheep) – there is continual microbial fermentation of dietary fiber. For this reason, horses are
classified as hindgut fermenters. In fact, normal function of the hindgut is heavily reliant on an adequate
supply of dietary fiber. This is a key point – without adequate dietary fiber, the horse is predisposed to
nutritional imbalances and colic problems.
The digestive process begins with the prehension of food, that is, food is grasped using a combination of the
lips, tongue and teeth. When eating tightly packed hay, larger muscles of the head and neck are also used to
grab and pull feed into the mouth. After prehension, the food is chewed (masticated) – this is an extremely
important part of the digestive process – digestion is most efficient when hay and other fibrous feeds are
ground into small pieces. Proper mastication of whole grains such as oats is also important to ensure optimal
digestion in the small intestine. That is why it is so important that the teeth are in good working order. Poor
teeth, a common problem in older horses, will result in decreased feed intake and weight loss, particularly in
horses on an all-forage diet. Quidding, the dropping of partially chewed feed from the mouth, is a sure sign of
dental woes. Choke (the lodging of a food bolus in the esophagus) and impaction colic can also occur when a
horse has poor dentition.
The type of feed has a dramatic effect on the speed of ingestion. A horse will chew between 3500 and 4500
times per kg of dry hay consumed, taking about 40 minutes to eat each kg of hay. Therefore, if 12 kg of hay is
provided each day, the horse will spend at least 8 hours feeding. When grains and other concentrate feeds are
substituted for fiber in the diet, the total time spent feeding will be markedly reduced – 1 kg of oats can be
consumed in 10 minutes or less, requiring only 850 chews. So, a diet of 7 kg hay and 5 kg oats will decrease
feeding time by 2 to 3 hours. Such reductions in feeding time are thought to cause boredom and other
behavioral problems (e.g. stable vices). This is another reason why fiber is such an important part of the
horse’s diet.
The horse produces saliva during chewing. Saliva moistens the ingesta thereby easing the passage of food
from the mouth to the stomach. Saliva is rich in bicarbonate, which helps to buffer the acid secretions
produced in the stomach. Here, the nature of the feed is also important – on a dry matter basis, twice as much
saliva is produced when horses eat hay or grass compared to rains and other concentrates. Diets high in grain
and low in forage will therefore decrease saliva flow and result in low gastric pH values, a risk factor for the
development of gastric ulcers. Only a limited amount of digestion occurs in the stomach. The stomach’s main
job is to further liquefy the incoming food and “feed” the ingesta into the small intestine, where digestion
really cranks into gear. However, gastric acid helps to breakdown some of the feed particles and the enzyme
pepsin initiates protein digestion. In fact, the stomach produces gastric acid on a continuous basis – this works
well when horses are grazing or nibbling on hay for much of the day because the incoming feed soaks up
these gastric juices. However, if the horse is meal fed (morning and evening) the stomach will empty for long
periods. In this situation, the acid can cause injury to the nonglandular portion of the stomach lining, gastric
ulcers being the end result.
The actual extraction and absorption of nutrients contained within food begins in earnest ingesta enters the
small intestine, a tube-like organ about 60 to 70 feet in length. Despite this considerable length, the ingesta
traverse the small intestine quickly. Some food enters the cecum within one hour and much of the ingesta will
reach the fermentation vat by 3 hours after eating. This rapid transit reflects the coordinated activity of the
nerves and muscles contained within the walls of the small intestine. Factors such as meal size, feed type and
exercise will influence transit time. Big grain meals result in rapid gastric emptying and intestinal transit and a
reduction in the digestion of the available starch. More on this later. Pelleted and ground feeds also tend to
move faster through the small intestine than fibrous feeds such as hay and grass. Exercise also results in a
moderate speeding of intestinal transit.
Sugar, Fat, and Protein
The small intestine is the primary site for the digestion and absorption of sugar and starch, protein and fat.
The fat-soluble vitamins (A, D, E and K), calcium and some phosphorus are also absorbed from the small
intestine. Let’s first deal with sugar and starch. Molasses is perhaps the best-recognized source of dietary
sugar for the horse – some “sweet feeds” are up to 10 percent molasses although the current trend is for lower
amounts. However, pasture grasses are by far the most important source of sugar; a horse grazing full time
could consume up to 2 kg of sugar (nutritionists use the term water-soluble carbohydrate or WSC). Sun-cured
hay has a lower WSC content as there is loss following harvest.
Starch is the plant world’s version of glycogen, the body’s storage carbohydrate – a huge number of glucose
molecules are linked by chemical bonds, forming a single structure. Starch is a major component of cereal
grains – oats are about 50 percent starch while corn is between 65 and 70 percent starch. The simple sugars in
molasses and grasses are easily digested; glucose is absorbed directly into the bloodstream while enzymes
located on the small intestinal lining make other sugars available to the body. Starch is a slightly different
story; the first step involves its breakdown to smaller sugars. Then, the enzymes on the intestinal lining act on
smaller sugars until they are in an absorbable form.
Amylase, an enzyme released by the pancreas when ingesta enter the duodenum, is the catalyst for the first
step. Unfortunately, compared to other mammals, amylase is in short supply in the horse. As a result, the
horse has a limited capacity to digest starch – the upper limit probably varies between horses but as a general
rule, a single grain or concentrate meal should contain no more than 5 lb. The starch story is further
complicated by the fact that digestibility of starch varies between the grains. For example, the starch in whole
corn is very poorly digestible. Fortunately, most manufactured feeds contain grains that have been processed
to greatly improve starch digestibility in the small intestine. Even so, with grain feeding, (particularly large
meals) there is always a risk that undigested starch will reach the large intestine. The digestion of protein and
fat is more straightforward. Enzymes from the pancreas and those present on the intestinal lining digest
proteins to their constituent amino acids, which are absorbed into the bloodstream.
Even though the “natural” equine diet is very low in fat, horses can digest fairly large quantities. Studies have
shown that horses can tolerate a 10 percent fat diet (total diet), although there should be a gradual increase to
this level to allow the digestive system to adjust.
The Boiler Room
The large intestine begins with the cecum, a structure that lies in the right flank area. This organ is 3 to 4 feet
long and holds up to 15 gallons of fluid and ingesta. Adjoining the cecum is the large colon, the largest single
structure in the digestive tract (about 40 percent of total capacity). Like the rumen of the cow, the cecum and
large colon work like a fermentation vat. Literally billions of microorganisms (bacteria and protozoa) do the
digestive work, producing enzymes that are able to breakdown the fibrous portion of the diet. This process is
much more time-consuming compared to digestion in the small intestine and the ingesta dwell in the large
intestine for upwards of 36-48 hours.
Dietary fiber is the portion of the ingesta not affected by the horse’s own digestive enzymes. There are many
(confusing) chemical and physical definitions of dietary fiber, but basically we are talking about the structural
components of plant material. Some of this fiber can be digested by microbial enzymes, particularly cellulose
and hemicellulose. On the other hand, lignin – another fiber form – is not digestible and will be passed in the
feces. The type of dietary fiber greatly influences its nutritional value – for example, over-mature grass hay
with relatively high in lignin, which depresses digestibility of the fiber. Other fiber sources such as young
grass, beet pulp and soy hulls are highly digestible.
The products of the fermentation process are the volatile fatty acids (VFA’s) acetate, butyrate and proprionate,
heat, water and gas. The VFA’s are absorbed into the bloodstream, providing an extremely important source
of energy for the horse. Microbial enzymes also break down undigested proteins, which enter the large
intestine, although the horse does not use this protein. Instead, the main end product of this process –
ammonia – is used by the bacteria to produce proteins that are needed for their own growth and survival. On
the other hand, vitamin K, another product of microbial activity, is absorbed into the horse’s bloodstream. As
a result, in most circumstances the horse does not require vitamin K in its diet.
Another very important function of the large intestine is the absorption of water. Each day, a huge quantity of
water is secreted into the small intestine as part of the digestive process – about 30 gallons (100 liters) for a
500 kg (1100 lb) horse. As the ingesta moves down the various secretions of the large colon, much of this
fluid is reabsorbed allowing the formation of semi-solid fecal material. The final step in the digestive process
occurs in the small colon, where the waste material is formed into fecal balls that are evacuated through the
rectum and anus.
In conclusion, remember that the horse’s digestive system functions best when it is fed a predominantly
forage diet on an almost continuous basis. Problems are much more likely when they are fed a relatively high
concentrate, low forage diet, particularly when given two (or even one) large meals per day. Yes, the
performance horse needs more energy than can be supplied by an all-forage diet, but try to spread the daily
grain/concentrate allotment over more meals e.g. three rather than one of two. Finally, allow the horse to
nibble on hay (or better, pasture) as much as possible.