FACULTY OF AGRICULTURAL

SCIENCES AND ALLIED

INDUSTRIES
TOPIC: Digestive System of Cattle and poultry

Digestive System of Cattle

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. Cattle
have 32 teeth. They have 6 incisors and 2 canines in the front on the bot 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.

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.

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. 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.

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.
 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.

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 the increased rumen size and pressure interferes with
normal breathing.

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.

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.

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 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.

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.

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 Digestive System of poultry

The digestive system consists of the alimentary canal along which the food
passes after eating to where the residual wastes are eliminated from the body,
together with the liver and the pancreas. The digestive system is responsible for the
ingestion of food, its breakdown into its constituent nutrients and their absorption into
the blood stream, and the elimination of wastes from this process.
The liver produces bile and is associated with the metabolism of nutrients together
with a number of other functions. The main function of the pancreas is the production
of digestive enzymes and special compounds called hormones.
The alimentary canal
The alimentary canal is a long tube-like organ that starts at the beak and ends
with the vent or cloaca in the abdominal region. Generally the alimentary canal has
layers of muscle that run lengthwise and around it and is lined with mucous
membranes. Glands that produce important digestive juices are found in different
locations of the canal. The nutrients from the food, after digestion, are absorbed
through the wall of the alimentary canal into the circulatory system for transport to
the liver or other parts of the body. The waste remaining is eliminated from the body
via the cloaca or vent.
Mouth structure
Fowls don’t have lips and cheeks, they instead have a beak which is an area
of dense and horny skin lying over the mandible and incisive bones that serve as the
bony foundation. There are no teeth. The so called egg tooth found on the end of the
beak of newly hatched chickens is an aid to their escape from the egg at hatching
and disappears after a day or two. The hard palate that forms the roof of the mouth,
presents a long, narrow median (median – along the middle) slit that communicates
with the nasal cavity. The hard palate has five transverse rows of backwardly
pointing, hard, conical papillae. Numerous ducts of the salivary glands pierce the
hard palate to release their secretions into the mouth cavity.
Salivary glands
A thick layer of stratified squamous epithelium covers the free surface. The
salivary glands run the whole length of the hard palate, the groups of glands merging
to form one mass of glandular tissue under the epithelium. Lymphoid tissue is found
in most glands.
The salivary glands are:
1. Maxillary – in the roof of the mouth
2. Palatine – on either side of the nasal opening in the roof of the mouth
3. Apheno-pteryoid glands – in the roof of the pharynx on each side of the common
opening for the eustachian tubes (the eustachian tubes connect the middle ear to
the mouth and their function is to equalise the air pressure on each side of the
tympanic membrane in the ear)
4. Anterior sub-mandible glands – in the angle formed by the union of the upper and
lower beaks or mandibles
5. Posterior sub-mandibular glands
6. Lingual glands – in the tongue
7. Crico-arytenoid glands – around the glottis
8. A small gland in the angle of the mouth

Pharynx and tongue

The pharynx is continuous with, and follows, the mouth. The combined cavity
of the mouth and the pharynx is often referred to as the oropharynx. The common
opening for the two eustachian tubes is located in the middle of its dorsal wall (roof).
The tongue is long and pointed and conforms to the shape of the beak in which it
operates. The epithelium of the tongue is thick and horny, especially towards the tip.
A transverse row of simple, large and horny papillae with their tips directed towards
the rear of the mouth cavity are located on the posterior end. The hyoid bone
provides the framework to support the tongue. The entoglossal bone extends
longitudinally in the median plane. Small patches of lymphatic tissue are located
throughout the corium. Mucous glands are located in the tongue with short ducts
directed towards the rear. Some believe that there are taste buds located on the
tongue, but this belief is not universally held. In any case, the sense of taste appears
to be very weak if at all present.
The mouth has two major functions:
1. To pick up the food particles.
2. To direct the food into the oesophagus – as part of the bird’s eating behaviour.

Oesophagus, crop and proventriculus

The oesophagus is wide and is capable of being significantly stretched. It
connects the mouth region to the crop in close association with the trachea. The
crop is a large dilation of the oesophagus located just prior to where the oesophagus
enters the thoracic cavity. The crop provides the capacity to hold food for some time
before further digestion commences. This capacity enables the bird to take its food
as “meals” at time intervals but permits continuous digestion. Inside the thoracic
cavity, the oesophagus enters or becomes the proventriculus which is a very
glandular part of the digestive tract (often called the glandular stomach).
The wall of the oesophagus is composed of four layers of tissue, the
innermost being mucous membrane. The mucous membrane is an important barrier
to the entry of microbes and the mucous it produces is a lubricant that aids the
passage of the food along the alimentary canal. The structure below the crop is
similar to that above except there is less lymphoid tissue below the crop. The crop
structure is similar to that of the oesophagus except there are no glands present in
fowls. Ducks and geese have glands in the crop mucous membranes. In pigeons the
surface cells of the crop slough off during brooding to form pigeon’s milk which is
used to feed the baby pigeons in the nest.
Proventriculus
The glandular stomach, or proventriculus, is relatively small and tubular. The wall is
very thick and is composed of five layers:
1. Outer serous membrane
2. Muscle layer composed of three separate layers:
o Two thin longitudinal layers
o Thick circular layer
3. Layer of areolar tissue containing blood and lymph vessels
4. Thick layer composed mainly of glandular tissue
5. Mucous membrane

The glands form the greater part of the thickness of the organ. Simple single
glands group to form lobules each of which converges into a common cavity near the
surface. The cavities converge to form a common duct that leads to the surface
through the apex of a small papilla (see figure below). These glands produce a
number of juices or enzymes that are used in the digestion or breaking down of food
into its constituent nutrients. The mucous membrane is raised into folds and between
these folds are numerous simple tubular glands that produce hydrochloric acid as
well as lymphoid tissue.
Gizzard
The muscular stomach or gizzard is located immediately after the
proventriculus, partly between the lobes and partly behind the left lobe of the liver. It
has a flattened, rounded shape somewhat like a convex lens, with one side slightly
larger than the other. Each surface is covered by a glistening layer of tendinous
tissue which is thicker at the centre and becoming thinner towards the edges. Under
this outer layer there are located very powerful masses of red muscle. The inner
surface is lined with a creamy-coloured, thick, horny tissue raised in ridges. The
gizzard almost always contains quantities of hard objects such as gravel or other grit
that aids in the disintegration of food, which is the primary function of the gizzard.
The entrance from the proventriculus and the exit to the duodenum are close
together and dorsal in location. The gizzard consists of a number of layers of tissues,
some of which contain straight tubular glands. The innermost layer is a strong,
flexible skin that is able to withstand the potentially damaging effects of the muscular
action grinding the food often in the presence of stones or other insoluble material.
The glands of the gizzard produce a liquid which is a keratinised material that
passes to the surface of the horny lining where it hardens to replace tissue worn
away by the grinding action of the organ.

The small intestine

The small intestine begins at the exit from the gizzard and ends at the junction of
the small intestine, caeca and colon. It is relatively long and has a constant diameter.
Of the three parts of the mammalian small intestine, the duodenum, jejunum and
ileum, only the duodenum can be easily distinguished in the fowl. There is no clear
demarcation between the jejunum and ileum and the small intestine appears as one
long tube. Much of the digestion of the food and all of the absorption of the nutrients
takes place in the small intestine and hence its structure is quite important. The
structure is as follows:
1. Serosa – a serous membrane on the outside of the intestine.
2. A layer of longitudinal muscle – fibres run along the length of the intestine.
3. A layer of circular muscle – three times as thick as the longitudinal muscle.
Located between the two muscle layers are:
o Blood vessels
o Lymph vessels
o A network of nerve fibres
4. An ill-defined sub-mucosa – the areolar of the oesophagus.
 5. Mucous membrane consisting of:
o A thick muscularis mucosae of longitudinal and circular muscle
o Corium – many glands, lymphoid tissue, muscle fibres and a variety of
free cells
o Epithelium or surface
The small intestine has a number of very important functions:
1. Produces a number of enzymes involved in the digestion process
2. Site of much of the digestion of the food
3. Site of much of the absorption of food

Villi
When a piece of the small intestine is immersed in water it takes on a very
velvety appearance because of the presence of villi – long flattened, fingerlike
projections that extend into the lumen (inside) of the intestine like flexible fingers.
The villi are very actively involved in the absorption process. A single layer of
columnar epithelium together with goblet cells covers the lining. The goblet cells
secrete mucous. Permanent folds in the mucous membrane called the “valves of
kerkring” are located at the proximal end (closest to the front) of the duodenum.
A lacteal (lymph vessels), capillaries, bundles of plain muscle fibres, nerves
and other tissues and cells occupy the core of the villus. The villi have the function of
providing a vastly increased surface area for the more efficient absorption of the
nutrients. The efficiency of the absorption is influenced by the surface area available
for the nutrients to move through i.e. the more villi the better the absorption. They
also provide a means of concentrating the nutrients collection ability once they have
moved through the intestine wall.
Duodenum
After the duodenum the small intestine forms a coil and is suspended from the
dorsal wall of the abdominal wall by a thin membrane called the mesentery. This
membrane carries the blood vessels associated with the intestine. The duodenum
starts at the gizzard and forms an elongated loop that is approximately 20
centimetres long. The pancreas lies between the arms of the loop and is attached
to, and actually holds together, each arm of the duodenum.
Lymphoid tissue in the duodenum is very plentiful and is usually located in the
corium. The lymphoid tissue collects the lymph and the lymph vessels transport fluid,
other than blood, that is found in the spaces between cells and tissues until it passes
into the blood system. Bile ducts from the gall bladder that are attached to the liver
and two to three pancreatic ducts enter the small intestine by a common papilla at
the caudal end (closest to the rear) of the duodenum. The pancreas is a very
important organ in the process of digesting food and it is attached to each side of the
duodenal loop and lies between the two arms.

Jejunum and the ileum

The jejunum and the ileum, together about 120 cm long, commence at the
caudal end of the duodenum where the bile and the pancreatic duct papilla are
located and terminates at the ileo-caecal-colic junction. This junction is where the
small intestine, the two caeca and the colon all meet. This portion of the small
intestine is similar in structure to the duodenum except that:
1. It is suspended in the mesentery
2. The villi are shorter
3. There is less lymphoid tissue
Meckel’s Diverticulum is a constant feature about half way along the small intestine
and appears as a small projection on the outer surface of the small intestine. This
projection is where the yolk sac was attached during the development of the embryo.
Large intestine
The large intestine is very short and does not differ to any extent from the
calibre of the small intestine. It runs in nearly a straight line below the vertebrae and
ends at the cloaca. Sometimes this section is referred to as the colon and the rectum
(the rectum being the terminal section). The bursa of fabricius is located
immediately above the cloaca of young birds but disappears when the birds have
reached approximately one year old.

Caeca
The two caeca or blind pouches are about 16-18 centimetres long in the adult.
They extend along the line of the small intestine towards the liver and are closely
attached to the small intestine along their length by the mesentery. Each caecum
has three main parts:
1. A narrow base with thick walls arising at the ileo-colic-caecal junction
2. Middle part with thin walls
3. The wide blind apex with fairly thick walls
The structure of the caeca is as follows:
1. Serous membrane
2. Outer longitudinal muscle
3. Circular muscle
4. Inner longitudinal muscle forming the muscularis mucosae of the mucous
membrane

Cloaca
The large intestine terminates in the front part of the cloaca. The cloaca is a
tubular cavity opening to the exterior of the body and is common to the digestive and
urogenital tract. The structure of the cloaca is very similar to that of the intestine
except that the muscularis mucosa disappears near the vent. It divides into three
chambers, each separated by a constriction not readily defined:
1. The copradaeum – a continuation of the colon-rectum
2. The urodaeum – middle part into which the ureters and genital ducts open
3. The proctodaeum – opens to the exterior of the vent. Birds less than one year old
have a dorsal opening leading into the blind, rounded sac – the bursa of fabricius