Front Cover
 Large intestine

Title: 4-H horse program : horse science
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00078697/00007
 Material Information
Title: 4-H horse program : horse science
Physical Description: Book
Creator: 4-H Youth Development Program, Florida Cooperative Extension Service, University of Florida
Publisher: 4-H Youth Development Program, Florida Cooperative Extension Service, University of Florida
Subject: University of Florida.   ( lcsh )
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00078697
Volume ID: VID00007
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida

Table of Contents
    Front Cover
        Page 1
        Page 2
        Page 3
        Page 4 (MULTIPLE)
    Large intestine
        Page 5
        Page 6
        Page 7
        Page 8
Full Text


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida

horse science








This educational material has been prepared for 4-H use by the Cooperative Extension Services of the U.S.
Department of Agriculture and State Land-Grant Universities in cooperation with the National 4-H Council and the
American Quarter Horse Association.

Trade or brand names used in the publications are used only for the purpose of educational information. The
information given herein is supplied with the understanding that no discrimination is intended and no endorsement
of products or breeds of horses by the Federal Extension Service or State Cooperative Extension Services is
implied, nor does it imply approval of products or breeds of horses to the exclusion of others which may also be

This material was originally published by the National 4-H Council, 7100 Connecticut Avenue, Chevy Chase,
Maryland 20815.

Programs and educational materials of National 4-H Council are available to all persons regardless of race, color,
sex, age, religion, national origin or handicap. Council is an equal opportunity employer.

Horse Science: The Digestive System of the Horse

The digestive system of the horse is different from that
of the other farm animals. Although the horse has a single
compartment stomach like man, the pig, and the dog, the
horse can utilize roughages like the cow which is a ruminant.
This is possible because the horse has a special type of
The digestive system is composed of the alimentary
canal and its accessory organs. The alimentary canal is a
hollow tube which extends from the mouth to the anus and
has the following parts: mouth, pharynx, esophagus,
stomach, small intestine, large intestine, and anus. Teeth,
tongue, salivary glands, liver, and pancreas are the accessory
Digestion is the process of preparation of food for
absorption from the alimentary canal into the blood stream
and elimination of the unabsorbed residue from the body.
The digestive process includes the combined effects of
mechanical, secretary, chemical, and microbiological
factors. The mechanical factors are chewing (mastication),
swallowing deglutitionn), movements of stomach and
intestines, and elimination of residue (defecation). The
digestive glands secrete digestive juices. Bacteria and
possibly protozoa are the microbial influences.
Understanding the structure (anatomy) and function
(physiology) of the unusual digestive system of your horse
helps you appreciate proper feeding of your horse.


The mouth is the first part of the tract, and the first act
of digestion is grasping of food prehensionn) to convey it
into the mouth. The horse's upper lip is the main structure in
grasping food because it is sensitive, strong, and mobile. In
grazing the action of the lip places the grass between the
front (incisor) teeth which cut the grass off. In manger
feeding, the loose food is collected by the lip with the aid of
the tongue. Water and milk are drawn into the mouth by
suction caused by a negative pressure in the mouth created
largely by the action of the tongue. SMALL INTESTINE
4-5 FEET 48 QTS.

Page 3

Mastication (chewing) is the mechanical reduction of
food into finely divided particles which provide a greater
surface area for the action of digestive juices. Mastication
also mixes the food with saliva which moistens the food thus
facilitating chewing and swallowing. This is especially
helpful with dry foods such as hays. Saliva is a secretion
from 3 sets of paired glands parotidd, submaxillary, and
sublingual) and other small glands found in the mouth.
Water makes up 99% of the horse's saliva with the other 1%
composed of inorganic salts (ions), and proteins. There are
no enzymes in the saliva of the horse. The secretion of saliva
in the horse is stimulated by the scratching (mechanical
action) of food on the mucous membrane of the inner
cheeks. It has been estimated that a horse will secrete about
10 gallons of saliva in 24 hours. Hay will absorb 4 times its
weight of saliva while oats will absorb about its own weight:
6 lbs. hay + saliva = 30 lbs.; 6 lbs. oats + saliva = 12 lbs.
The horse is well equipped for chewing tough, coarse
feeds with a set of 40 upper and lower teeth in the male: 12
incisors or front, 4 canines, and 24 premolars and molars or
cheek teeth. Mares have 36 teeth since they usually do not
have canine teeth which in the male are located in the space
between the incisors and premolars. Jaw movement is
vertical (up and down) and lateral (side to side). Because of
this, the upper jaw is wider than the lower; therefore,
mastication can occur on only one side of the mouth at a
time. The cheek teeth wear sharp edges on the inside of the
lower teeth and on the outside of the upper teeth because of
the lateral movement. These sharp edges cause damage to
the tongue and cheek resulting in the horse eating slowly and
wasting feed. Floating the teeth will remove these sharp
edges. An annual check-up will prevent this and other dental
problems. The lower incisors serve another useful function -
the detection of age. (see section 4)



130 OTS

June 1989

Horse Science: The Digestive System of the Horse

The horse is a relatively slow eater and chews food
thoroughly requiring 15-20 minutes to eat a pound of hay
and 5-10 minutes to eat a pound of grain.
Deglutition (swallowing) is the complex act, involving
a number of muscles and nerves, of conveying food from the
mouth through the pharynx and esophagus to the stomach.


The pharynx is a 6-inch muscular, funnel-shaped sac
belonging to the digestive and respiratory tracts whose
passages cross in this region. Food must move through the
pharynx quickly so that it will not enter the larynx
(windpipe) or be forced into the nasal passages. Once food
and water enter the pharynx, it cannot return to the mouth
due to the blocking action of the soft palate. Horses for this
same reason cannot breathe through the mouth.


The esophagus is a muscular tube about 50 to 60 inches
in length which extends from the pharynx down the left side
of the neck to the stomach. Solid and semisolid food moves
down the esophagus by wave-like contractions (peristalsis),
while liquids are squirted down. These movements can be
seen by observing a horse eating and drinking. Choke can
occur in horses when food, especially dry grain, and other
materials become lodged in the esophagus. Food and water
will be observed returning through the nostrils. Peristalsis is
a one-way action in the horse from the pharynx to the
stomach; because of this, it is very difficult for the horse to
vomit. The act of vomiting usually results in the rupture of
the stomach or pneumonia from the vomited material being
forced into the larynx then to the lungs.


The opening of the esophagus into the stomach, the
cardia, is closed by a powerful involuntary ring-like muscle
(sphincter). This also reduces the occurrence of vomiting
since it is very difficult for material to pass from the stomach
back into the esophagus. The horse has the smallest stomach
compared with other farm animals. With only a capacity of
8 to 17 quarts, the horse should be fed portions of the daily
ration 2 or 3 times daily rather than one large feeding.
Several types of glands and specialized cells are found
in the stomach walls. Gastric juice and mucous secretions
are produced by these specialized glands and cells. Gastric
juice contains hydrochloric acid (HC1) and two enzymes,
pepsin and gastric lipase. Pepsin is the enzyme which helps
digest proteins. Gastric lipase helps digest fats into
constituent fatty acids and glycerol; however, fat digestion
is mainly by pancreatic lipase in the small intestine.

Page 4

Hydrochloric acid (HC1) activates pepsin and cooperates
with pepsin in the breakdown of protein. The rate of
secretion of gastric juices is a continuous process with the
rate increasing when food is eaten.
In the horse's stomach food has a tendency to arrange
itself in layers. The first food passes into the bottom region
of the stomach with subsequent food lying on or around the
first food to form layers. The partially digested food does
not leave the stomach until it has reached two-thirds of its
capacity. Excess food consumed beyond the capacity of the
stomach along with partially digested food pass on into the
intestine. The emptying of the stomach is a continuous
process during digestion. It requires a 24 hour fast to
completely empty a horse's stomach. Stomach movement
due to muscular contraction mixes the food with gastric
juices and passes the ingesta into the duodenum.
When to water a horse has always been an important
question. It has long been recommended never to water a
horse during or immediately following eating because the
water will wash food out of the stomach. This is not true.
Drinking during or following a meal has no harmful effect
on digestion since most of the water passes directly from the
esophageal opening to the intestine opening which are
located quite close together due to the U-shaped form of the
Horses are prone to digestive disorders originating in
the stomach. Feeding ground grains which are easily packed
into a doughy mass, sudden changes in feeding, failure to
reduce the grain ration during idle periods, and ingestion of
excessive amounts of water are a few causes of stomach


The small intestine is 70 feet in length and 3 to 4 inches
in diameter; it extends from the stomach to the large
intestine; it has three parts the duodenum, jejunum, and
ileum. The capacity of the small intestine is 48 quarts. The
material leaving the stomach and entering the small intestine
is known as chyme, and it is a fluid or semi-fluid. Two main
types of factors influencing digestion in the small intestine
are movements of the intestinal wall and secretions from the
pancreas (pancreatic juice), the liver (bile), and the intestinal
glands (intestinal juice).
The pancreatic juice is produced by the pancreas gland
and contains several enzymes. Trypsin (activated
trypsinogen) converts proteins and partly hydrolyzed
proteins into peptides and amino acids. Pancreatic lipase
hydrolyzes fats to fatty acids and glycerol, and pancreatic
amylase which breaks down starch to maltose. Bile, a
secretion from the liver, activates pancreatic lipase, assists
in fat emulsification, and aids in absorption of fatty acids.
The bile duct and pancreatic duct empty into the 3 to 4 feet
long duodenum about 5 to 6 inch from the pylorus, the
stomach opening into the intestine. In

June 1989

Horse Science: The Digestive System of the Horse

other farm animals, bile is temporarily stored in a
gallbladder. The horse does not have a gallbladder; there is
a direct secretion of bile into the small intestine from the
Simple tubular glands are found throughout the small
and large intestine which secrete the sugar digesting
enzymes maltase, sucrase, and lactase. Each of these
enzymes attacks the individual sugar with the name similar
to its own (maltose, sucrose, and lactose). The enzyme
breaks the sugar into glucose which can be absorbed. These
simple tubular glands also secrete a lipase similar to
pancreatic lipase.
Absorption of many nutrients (Amino acids, sugars,
fatty acids, minerals, and vitamins) occurs in the small
intestine which is well equipped with small projections
called villi. Villi increase the surface area which enhances
absorption. Intestinal movements mix the ingesta with the
digestive secretions, enhance absorption, move the material
through the intestines, expel the residues, and assist in the
flow of blood and lymph through the vessels of the intestinal
The great length of the small intestine leads to many
problems such as twisted or telescoped intestine.


Material which is not or cannot be digested in the small
intestine passes into the large intestine which is divided into
the cecum, large colon, small colon, rectum, and terminates
at the anus. The important digestive action of the cecum and
colon is due to the presence of bacteria and possibly
protozoa (one celled animals) which (1) digest cellulose, the
fibrous part of roughages, and other carbohydrates such as
starch and sugars to produce energy yielding volatile fatty
acids; (2) synthesize B-vitamins; and (3) synthesize amino
acids. Absorption of volatile fatty acids apparently occurs in
the colon.


Page 5

B vitamins are definitely synthesized by the bacteria of
the large intestine; however, in certain situations the
absorption of most of them may not be adequate to meet the
need of the horse. On normal diets, B vitamin deficiency
does not occur in the horse so adequate quantities of B
vitamins are available either (1) in the feed (diet) or (2) by
bacterial synthesis.

CECUM. The cecum, blind gut, lies between the small
intestine and large colon. Its average length is 4 feet with a
capacity of 28 to 32 quarts. It extends into the right flank.
The presence of food in the stomach causes an emptying of
the cecum into the large colon. Because of the
microorganism digestive action in the cecum, it is a
functional appendix.

LARGE COLON. The large colon with a diameter of 8 to
10 inches is 10 to 12 feet long and has a capacity of 80
quarts. The large colon extends from the cecum to the small
colon where it terminates in a funnel shaped restriction.
Because it is usually expanded with food, impactions may
occur. Impactions occur also in the cecum and small colon.

SMALL COLON. The small colon extends from the large
colon to the rectum. It is from 10 to 12 feet in length with a
diameter of 3 to 4 inches. Water is reabsorbed from the
contents of the small colon and the characteristic balls of
feces are formed. Feces is the waste matter of digestion and
contains water, indigestible and undigested food residues,
cells sloughed off of the intestinal wall, and remains of
digestive secretions.

RECTUM. The rectum extends 1 foot in length from the
small colon to the terminal part of the digestive tract, the
A horse normally voids 33 to 50 lbs. of feces per day.
Vigorous horses defecate 5 to 12 times daily.


June 1989

Horse Science: The Digestive System of the Horse


June 1989

Page 6

Horse Science: The Digestive System of the Horse


June 1989

Page 7

1. This document is section 7 of 14 of 4HHSGO1, which supersedes CO 201, one of a series of the 4-H Youth
Development Program, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University
of Florida. Date first printed August 1965. Date revised June 1989. Please visit the FAIRS Website at

Cooperative Extension Service
Institute of Food and Agricultural Sciences

2. Frederick Harper, Rutgers The State University. Debbie Glauer, member of 4-H Animal Science Design Team,
Department of Family, Youth and Community Science, Cooperative Extension Service, Institute of Food and
Agricultural Sciences, University of Florida, Gainesville, 32611.

Taylor Waddill, Director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of
the May 8 and June 30, 1914 Acts of Congress; and is authorized to provide research, educational information and other services only to
individuals and institutions that function without regard to race, color, age, sex, handicap or national origin. The information in this publication
is available in alternate formats. Single copies of extension publications (excluding 4-H and youth publications) are available free to Florida
residents from county extension offices. Information on copies for out-of-state purchase is available from Publications Distribution Center,
University of Florida, PO Box 110011, Gainesville, FL 32611-0011. Information about alternate formats is available from Educational Media and
Services, University of Florida, PO Box 110810, Gainesville, FL 32611-0810. This information was published June 1989 as CO 201, which is
superseded by 4HHSG01, Florida Cooperative Extension Service.

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