Download The Equine Digestive System

The Equine Digestive
System
Objectives

Discuss internal organs

Identify the structures of the digestive
system

Recognize functions of the organs
comprising the digestive system
Digestive System

Monogastric - having one stomach

Herbivores - plant-eating animals

Digestive system anatomically developed
to continually digest small amount of food
Digestive System

Eat simple-looking feeds containing
complex chemical substances


dramatic changes during digestive process
before feed is used as energy
Digestion - process of mechanical and
chemical breakdown of feed into simple
structures
Digestive System

Simple structures are:

soluble (able to be dissolved) in water

absorbed through mucous membranes lining
intestinal tract
 membranes
that line cavities in the body and
connects inside of cavity to outside
Digestive System

Unique

Small, efficient stomach for grain utilization

Large cecum and colon for roughage
utilization
Digestive System

Purpose - process feed into component
nutrients for:

Absorption - process of taking in by various
means

Utilization
Digestive System

Alimentary canal (digestive system) muscular hollow tube beginning at mouth
and ending at anus

Loops on itself many times

Size - One inch in diameter at small
intestine to eight inches at large colon
Digestive System
Component parts include:
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Rectum
 Anus
Digestive System
Digestive System
Large intestine consists of the:
Cecum
 Ventral and dorsal colon
 Transverse colon
 Small colon
 Rectum

Digestive System

Alimentary tract with help of teeth, tongue,
salivary glands, liver, and pancreas
prepare feed for absorption and eliminates
waste

Few feeds eaten are in simple forms ready
to be absorbed and utilized
Digestive System
Most feeds require substantial change by:
 Mechanical Action

Secretory Action - products produced by
glands that aid in digestion

Chemical Action

Microbial Action - digestion by very minute
organisms
Digestive System
Mechanical actions include:
 Mastication – chewing

Deglutition – swallowing

Intestinal movements

Defecation - elimination of waste
Anatomy of the Digestive
System
Mouth

First section of alimentary canal

Contains 24 molars and 12 incisors

Includes tongue and salivary glands
Mouth

Prehension -the grasping and moving of
feed into the mouth by a sensitive, mobile
upper lip

Precise - can graze grass almost into
ground

Sorts and selects hay
Mouth

Digestion - begins in mouth when feed is
masticated by the teeth


grinded and chewed by the mouth
Serves to reduce feed particle size
Mouth
Saliva:
 85 pounds (10 gallons) daily

Wets feed - Easier to pass through
esophagus

Enzymes - help digest carbohydrates

Produce large amounts only while chewing
Pharynx

Muscular

Funnel shape

Guides feed into esophagus

Located in upper back of mouth where
digestive and respiratory tracts cross
Pharynx

Once feed or water enters pharynx, it
cannot return because of blocking action
of soft palate

Epiglottis closes at the same time to
prevent feed from entering lungs
Esophagus

4 to 5 feet in length

Extends from mouth down left side of
neck, through the diaphragm, and to the
stomach

Moves feed and water to stomach by
progressive waves of muscular
contractions called peristalsis
Esophagus

Waves irreversible

Extreme muscle tone occurs at end of
esophagus
Esophagus

Extremely difficult to expel gases through
eructation


the act of expelling gas from the stomach
through the mouth
Stomach would rupture before vomiting
would occur
Stomach

U-shaped sac near diaphragm at front of
abdominal cavity

Sphincter acts as powerful muscle where
esophagus enters into stomach

Makes vomiting nearly impossible
Stomach

Small compared to other animals

10% of total capacity of entire digestive
tract

Capacity - two to four gallons

requires they eat two to three times daily
rather than just once
Stomach

Feed moves through rapidly

Frequent feeding in small amounts is more
efficient and better satisfies

Rate of passage is rapid in comparison to
other areas

Time required for something to move through
an area
Stomach

Reservoir for ingested feed while
subjecting it to gastric digestion


chemical breakdown of feedstuffs by the
stomach
Gastric juices, secreted by glands in the
mucous membrane of stomach, contain
hydrochloric acid, pepsin & gastric lipase
Stomach

Pepsin is a protease - enzyme that helps
digest protein into amino acids


building blocks of proteins
Gastric lipase - digest fat into fatty acids &
glycerol
Stomach

When two-thirds full, feed passes into
small intestine and continues as eating
continues

If horse eats too much at one time, some
will leave stomach without sufficient
digestive action

Leads to decreased efficiency
Stomach

Number of digestive disorders can occur

Caused by:
moldy feeds
 ground mashes
 sudden changes in feed
 feast-and-famine situations
 parasites

Stomach

Very little nutrient absorption takes place
in the stomach

Proteins and carbohydrates are only
partially digested
Small Intestine

2 inch by 60 foot tube

Holds approximately 12 gallons

Connects stomach to large intestine

Contains three parts: the duodenum, the
jejunum, and the ileum
Small Intestine

30% of the digestive tract

Folded into many loops and coils

2.5 to 4 hours for feed to pass
Small Intestine
Bloodworms
 cause blood clots

may result in colic or death

tend to lodge in the mesentery artery
which supplies blood to the intestines
Small Intestine

Small intestine and accessory organs, the
pancreas and liver, supply enzymes

Peristalsis mixes fluid contents of the
which are about 92-95% water

Pancreatic juices contain the enzymes
trypsin, pancreatic lipase, and amylase
Small Intestine

Trypsin - converts proteins into amino
acids which the small intestine absorbs

Primary site of protein digestion and
absorption of amino acids

Pancreatic lipase - breaks down fats to
glycerol and fatty acids
Small Intestine

Liver secretes bile
helps break down fat
 aids in fatty acid absorption
 activates pancreatic lipase


Most soluble carbohydrates digested in
small intestine
Small Intestine

End products of carbohydrate digestion
are glucose and volatile fatty acids which
are absorbed for energy

Absorbs nutrients, such as simple sugars,
fatty acids, amino acids, minerals, and
vitamins
Large Intestine

Composed of the cecum, large colon,
small colon, and rectum

Moves undigested materials from small
intestine to anus for elimination

50-60% of digestive tract
Large Intestine

Holds 30-35 gallons

25 feet long

Designed for utilization of plant fiber for
energy
Large Intestine

After ingesta leaves small intestine, it
enters into cecum


substances that have been taken into the
body by way of the digestive tract
Cecum serves as fermentation vat in
which enzymes break down fibrous plant
structures for digestion
Large Intestine

Carbohydrates such as cellulose that
escaped digestion in small intestine are
fermented in large intestine

Complex carbohydrate that is the main
component of the plant cell wall
Large Intestine

Can digest cellulose, starch, & sugars into
volatile fatty acids

supplies up to 25% of horse’s energy
Large Intestine

Cecum - primary site of water absorption

Rate of passage slower than in other
portions of digestive tract

36-48 hours
Rectum

Connects small colon to anus

Receives feces small colon has formed
into characteristic balls

Forty to fifty pounds of feces is voided
eight to twelve times a day
Rectum

Shape, size, and consistency of feces give
clues to overall health

Dry and hard - lack of water or protein

Too soft - Sick or eating diet that is too
laxative
Digestive System Disorders
Disorders

Because of the complex nature of the
digestive system, horses are predisposed
to digestive disorders

Susceptible to twisting and impaction of
the large intestine
Disorders

Sensitive to gases produced by microbial
digestion

Rapid fermentation may cause excessive
gas or lactic acid to be produced

can cause colic or laminitis
Colic

“Colic” - many painful digestive
disturbances with various causes

Improper feeding such as feeding too
much grain or suddenly changing the diet
can cause colic
Colic

Usually caused by gaseous products that
are part of microbial digestions

May cause swelling in digestive tract

Ingesting low quality, poorly digestible
feed can cause impaction of cecum and
colon
Colic

To avoid digestive disturbances, allow one
to two weeks to change from one feed to
another.
Laminitis

Occurs when inner hoof wall becomes
inflamed

Rapid changes in diet can cause certain
type of bacteria in cecum to die

Release large amounts of endotoxins
Laminitis

Endotoxins enter bloodstream and
decrease the amount of blood flow to
lamina

Commonly occurs when a horse is
switched from winter hay to pasture in the
spring
Summary

Purpose of digestive system is to process
feed into component nutrients for
absorption and utilization by the body

Very complex

Many digestive disorders
Summary

Monogastric

Eat relatively simple-looking foods that are
transformed to an easily digestible form
ALL RIGHTS RESERVED
Reproduction or redistribution of all, or
part, of this presentation without
written permission is prohibited.
Instructional Materials Service
Texas A&M University
2588 TAMUS
College Station, Texas 77843-2588
http://www-ims.tamu.edu
2008