Front Cover
 Specialized glossary
 Male reproductive organs
 Female reproductive organs
 Pregnancy and birth

Title: 4-H horse program : horse science
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00078697/00005
 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: VID00005
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
    Specialized glossary
        Page 3
    Male reproductive organs
        Page 4
    Female reproductive organs
        Page 5 (MULTIPLE)
    Pregnancy and birth
        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: Principles of Reproduction in Horses

The birth of a foal is the end of a wondrous process. It
starts with the merging of two tiny cells one from the
female animal (mare), one from the male (stallion). With the
joining of these cells, a new animal is conceived.
The cell from the female is called an egg, or ovum. The
cell from the male is a sperm. The egg and sperm are both
sex cells, the very special cells that contain the genetic
material an animal inherits from its parents. Two
microscopic cells will completely determine the genetic
makeup of the offspring. See the discussion of genes and
chromosomes in the guide sheet entitled "How Inheritance
Works in Horses".
The production of sex cells is a unique and interesting
process. Each of the two sexes has special organs to produce
sex cells and carry out the process of reproduction. These
are called the reproductive organs. Much of the reproductive
process is regulated by secretions from the body's mature
gland, the pituitary. A knowledge of many specialized terms
are essential for you to properly understand and discuss this
reproductive process.
Study This Specialized Glossary Before Proceeding


Accessory glands (ak-ses-o-ri). These glands are located
along the urethra of the male. They produce fluids that
nourish and preserve sperm.
Birth canal The birth canal includes the cervix and the
vagina of the female. They are the organs through which the
unborn animal passes at birth.
Cervix (sur viks). This is the narrow passage or doorway
between the female's vagina and uterus.
Corpus luteum (kor pus lu te-um). A solid mass that forms
in the follicle after the egg has left. It produces a hormone
which helps maintain pregnancy. It prevents other follicles
from developing while the unborn animal is growing in the
Epididymis (ep I-did I-mis). A mass of tubes connected to
the testicle. Its main function is to store sperm.
Estrogenic Hormones Hormones that stimulate the
development and maintenance of feminine sexual characters.
The principal estrogenic hormones are:
a) estradiol; b) estrone; c) estriol.
Estrus (es trus). The estrus period is commonly called
Fetus (fe tus). The unborn animal as it develops in the
Follicle (fol I-k 1). A bubble-like structure on the ovary
which contains an egg.
Follicle stimulating hormone (FSH). Comes from the
pituitary and causes follicle growth.

Page 3

Hormone (hor mon). A body-regulating chemical secreted
by a gland into the blood stream.
Infundibulum (in fun-dib u-lum). The funnel-like
membrane that surrounds the ovary. It catches the egg when
it is released by the ovary.
Luteinizing hormone (LH). Comes from the pituitary and
regulates corpus luteum in female and testosterone secretion
in male.
Nucleus (nu kle-us). The dense center of a cell. It contains
the genetic material.
Ovary (o va-ri). A female organ that produces eggs. There
are two ovaries.
Oviduct (o vi-dukt). The tube which carries the egg from
the ovary to the uterus.
Ovulation (o vu-la shun). The time when the follicle bursts
and the egg is released.
Ovum (o vum). Scientific name for egg.
Placenta (pla-sen ta). The membrane by which the fetus is
attached to the uterus. Nutrients from the mother pass into
the placenta and then through the navel cord to the fetus.
When the animal is born, the placenta is expelled. It is
commonly called the "afterbirth."
Pituitary This gland located at the base of the brain
secretes hormones which regulate the body.
Progesterone A steroid hormone secreted by the
hypertrophied cells of the corpus luteum. It inhibits the
action of estrogens. It aids in the development of the uterus
for implantation and effective nutrition of the embryo.
Prolactin A hormone produced in the anterior pituitary
gland. It initiates lactation or in the case of nursing mothers
milk secretion is stimulated.
Sex cells The egg and the sperm. They transmit genetic
material from the parents to the offspring.
Scrotum (skro tum). The sac-like pouch that suspends the
testicles outside the male animal.
Sperm Male sex cells produced in the testicles.
Semen (se men). Sperm mixed with fluids from the
accessory glands.
Testicle (tes ti-k 1). A male gland which produces sperm.
There are two testicles.
Urethra (u-re thra). The tube through which both semen
and urine pass through the penis of the male.
Uterus (u ter-us). The muscular, spongy organ of the
female where the unborn animal develops. It is commonly
called the womb.
Vagina (va-ji na). The canal which leads from the uterus to
outside the female. Sperm is deposited there by the male,
and the fetus passes through the vagina at birth.
Vas deferens (vas def e-renz). The tube that carries sperm
from the epididymis to the urethra in the male.

June 1989

Horse Science: Principles of Reproduction in Horses


The primary sex organ of the stallion is the testicle.
(There are 2 testicles.) The testicles produce sperm in the
mature individual and also produce a hormone called
testosterone. Testosterone regulates and maintains the male
reproductive tract in its functional state. Testosterone is also
responsible for the masculine appearance and behavior of
the stallion.
Each testicle contains a mass of minute, coiled tubules.
The inner walls or surface of these produce the sperm. The
numerous thousands of minute tubules merge into a series of
larger ducts which pass out of the testicle to a larger, coiled


tube located adjacent to the testicle. This tube, the
epididymis, is the place where sperm are stored while they
mature. Sperm formation in the male is a fairly continuous
The testicles and epididymides are located in the
scrotum which regulates the temperature of these structures.
The scrotal temperature is several degrees cooler than that
of the body cavity which is necessary for the normal
development of sperm.
From the epididymis, the sperm move through a tube,
the vas deferens, into the urethra. The urethra is the tube that
carries urine from the bladder through the penis. The urethra
also carries sperm from the junction with the vas deferens to
the end of the penis.
Along the urethra are the accessory glands. Their names
are the prostate, the seminal vesicles and cowpers gland.
They produce fluids that nourish and preserve the sperm.
During mating, the accessory glands discharge their fluids
into the urethra. This washes the sperm forward through the
penis. The combined fluid and sperm is called semen.
Puberty, or the capacity to produce sex cells, occurs in
the stallion at the age of approximately one year. This is not
a period of mature breeding capacity. Two-year-old stallions
may be used for limited breeding service. Breeding use of
the stallion should be deferred until after the age of two. Ask
your veterinarian or an experienced horseman to explain
care and management of the mature stallion to you.


June 1989

Page 4

Horse Science: Principles of Reproduction in Horses


The mare's reproductive organs are quite different from
the stallion's. The female produces the ova or eggs, receives
the sperm from the male, and provides a place for the
unborn animal to develop.
The primary sex organ of the mare is the ovary. Each of
the two ovaries is usually 2 to 3 inches long and somewhat
bean-shaped. The other portion of the female reproductive
tract is known as the duct system. It consists of the oviducts,
the uterus, the cervix, and the vagina. The various parts of
the duct system are connected together and attached
internally to the upper body wall by a series of ligaments.
The ovaries produce the eggs. Each egg is contained in
a bubble on an ovary. This bubble is called a follicle. There
are hundreds of follicles on each ovary. At the same time by
a process not completely understood, one or more follicles
begin to grow while the others remain small. The follicle
grows until it is about an inch in diameter. It is filled with a
fluid. The egg is suspended in the fluid. Near the time of
mating, a hormone causes the follicle to burst.
The fluid gushes out of the follicle, carrying the egg
with it. The egg is then trapped in a very thin membrane that
surrounds the ovary. Shaped like a funnel, this membrane is
called the infundibulum. The infundibulum narrows into a
tube called the oviduct. The oviduct carries the egg to the
uterus, or womb. The largest of the female reproductive
organs, the uterus is where the unborn young (the fetus) will
The uterus has a thick wall with heavy layers of
muscles. At birth, these muscles will contract with great
pressure to force the new animal through the cervix and
vagina (birth



Page 5

canal) and into the world. The lining of the uterus is soft
and spongy, containing a vast network of blood vessels. This
network of blood vessels provides a "bed" for the fertilized
egg to settle into and develop.


The estrous cycle of the mare may be divided into
phases, i.e., diestrus (quiet period); proestrus (preparation);
estrus (heat period). The average length of the estrous cycle
for mares is 22 days but may vary from 17 to 30 days.
Individual mares tend to retain their individual cycle
characteristics with regard to length of cycle and length of
The mare is called polyestrus because she cycles
continuously throughout the breeding season in the absence
of conception. The mare is called seasonally polyestrus
because there is seasonal fluctuation of the estrous cycle
with regard to length, intensity and regularity. Most mares
that exhibit no outward signs of estrus during winter months
are said to be anestrous (without estrus) during that time.
The estrous cycle may be irregular in the early spring.
The most easily recognized phase of the estrous cycle
is estrus (heat period) or the period of male receptivity. It is
caused by the relatively large amount of a hormone, estrogen
secreted during this state of rapid and maximum follicle
growth. The average length of estrus is 6 days but often
varies from 2 to 11 days. Periods usually decrease in length
as the summer progresses. Ask your veterinarian or an
experienced horseman to explain the external signs of estrus
and for instructions on management of your mare during the
breeding season.


June 1989

Horse Science: Principles of Reproduction in Horses

The period when a mare is out of estrus is generally
called diestrus. This phase or stage usually varies from 10 to
18 days. The first part of diestrus involves corpus luteum
development. In the absence of conception, the corpus
luteum regresses within a few days and new follicle
development once again takes place under the influence of
a hormone (FSH) from the pituitary gland. The period of
rapid follicle growth at the termination of diestrus is
commonly referred to proestrus.
Many mares are capable of first reproduction at 4 years
of age. Regular annual foaling is conducive to total life-time
production. In most cases it is advisable to have mares
examined for reproductive status prior to breeding. Policies
regarding general sanitation, safety, and medical aspects
should be observed in all equine breeding programs.
Fertilization is the process of the uniting of the sperm
and the ova. The tubular or duct portion of the female
reproductive tract undergoes rhythmic contractions during
estrus and this activity is stimulated by mating at which time
the sperm is deposited in the tract. This pulsating action plus
the locomotion of the sperm in a fluid medium transport the
sperm through the cervix and uterus into the oviducts. The
sperm and the egg unite in the oviduct.
Only one sperm fertilizes a single egg although several
million sperm may be present in the reproductive tract of the
female. Only one egg is usually present per conception in
horses. Sometimes a mare will produce two eggs and if both
are fertilized, twin embryos will start to develop. Identical
twins result from a different situation. In this case a single
egg divides into two independent cells or cell masses at a
very early stage of development. Twin embryos are
undesirable in horses because they are generally aborted
The egg produced by the mare is small in size although
it is much larger than a sperm. The egg has a nucleus which
contains the genetic material. The sperm has a much
different shape than the egg which is basically round. The
sperm has a head, a middle section and a tail. The physical
movement of the latter structure gives the sperm cell its
property of locomotion in a fluid medium. The genetic
material of the sperm cell is contained in the head section.
Upon fertilization, a sperm penetrates the outside
membrane of the egg and the head section is drawn into
contact and union with the nucleus of the egg; thus the
genetic composition of the new individual is established.
Fertilization is also the stimulus for the egg to divide and
grow to form the new individual.
The fertilized egg usually undergoes its initial cleavages
or divisions in the oviduct. Meanwhile, it is transported to
the uterus where development progresses.

Page 6


Pregnancy is the time during which the fertilized egg
develops in the uterus. This process is also known as
gestation. For a period of about six weeks, the cell mass
resulting from the fertilized egg grows as a "free floating"
object in the uterus. During this time, the fetal membranes
commence to form. Nourishment of the new individual
during this early stage is provided for by uterine secretions.
The hormone progesterone secreted by the corpus luteum
assist in regulating the reproductive tract during pregnancy.
At approximately 6 weeks of pregnancy, the placenta
attaches to the wall of the uterus and then provides for the
nourishment of the fetus. Nutrients and oxygen are carried
from the mare to the fetus and waste products from the fetus
are eliminated through the placenta. The navel cord connects
the fetus to the placenta.
The process of gestation in the mare requires about 340
days; however, it may vary from approximately 300 to more
than 400 days following breeding. The fetus develops
gradually although the most rapid period of growth takes
place during the last 3 or 4 months of pregnancy.
Successful pregnancy ends in birth or parturition. At the
proper time due to hormone action, the strong muscles of the
uterus contract forcing the new animal through the birth
canal and into the world. Until, now, the young animal
received nutrients and oxygen from its mother's blood
stream. But at birth the navel cord is broken. The animal
must live on its own. Apparently the breaking of the navel
cord stimulates the animal to breathe. This solves the
problem of oxygen. As for nutrients, the mother's body has
been preparing them for many weeks. The hormones
produced during pregnancy have stimulated the milk glands.
By the time of birth, they are ready to provide milk. Later,
the mare will expel the remainder of the fluids and placenta
to the completion of parturition. The entire process may
require several hours.
Milk production and "letdown" is initiated by hormones
secreted by the pituitary gland. The first milk or colostrum
is seen just prior to or after parturition. Colostrum is very
high in proteins and other nutrients which provide the foal
with resistance to infections. It is very important to the new
born foal that it receives the colostrum. The colostrum is
exhausted and replaced gradually with normal milk by about
two days after the initial nursing.
There will always be reproductive problems among
horses but interference may be minimized by good
management practices. An understanding of some of the
basic principles of the processes of reproduction can aid
horse breeders materially in dealing with difficulties likely
to be encountered.

June 1989

Horse Science: Principles of Reproduction in Horses


June 1989

Page 7

1. This document is section 5 of 14 of 4HHSG01, 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

2. Walter Smith, Kansas 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.

Cooperative Extension Service
Institute of Food and Agricultural Sciences

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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