STALLION
MANAGEMENT
Lesson
2
Stallion
Anatomy and Physiology
Anatomy
and Physiology of the Stallion
A very good book on the stallion is THE
STALLION, A BREEDING GUIDE FOR OWNERS AND HANDLERS by James P. McCall,
Ph.D. It is enjoyable reading and will break the monotony of some of the text
reading, when you need a break.
The Stallion Reproductive System
I. Anatomy &
Physiology (structure and function of the stallion reproductive system)
Click
Here To View a Power Point Presentation – Stallion Reproductive System Anatomy
a. External Genitalia
1. Testis
(Testicles) (2) – Which are found within the scrotum, have
a dual function. The testicles are considered both an exocrine gland (produces
a cellular component that is transferred through a duct system) and an
endocrine gland (produces a hormone that is absorbed through the blood stream
and carried throughout the tissues in the circulatory system. The exocrine
function of the testicles is the production of sperm cells. Sperm cells are
produced within the testicular tissue and require a slightly cooler environment
that normal body temperature. The scrotum acts as a thermo regulator in that it
is able to keep the testicles away from the body and therefore the temperature
of the testicular tissue is conducive to the production of live sperm cells.
The cremaster muscle, which attaches to each testicle is also a part of the
thermo-regulatory system and can contract and pull the testicles up closer to
the body during colder weather, and relax and drop the testicles further from
the body in warmer weather, thereby guaranteeing live sperm production. The pampiniform plexis, a convolution
of blood vessels supplying the testicular tissue with blood, is also part of
the thermo-regulatory system, in that it cools the blood going to the
testicles. The endocrine function of the testis is the production of the male
hormone testosterone. Testosterone initiates sperm production and development
and maintenance of masculine characteristics and is also responsible for the
libido (sex drive or sexual desire).
2. The Epididymis
connects the testicle to the vas deferens. The epididymis is where
sperm is stored. The vas deferens (deferent duct or ductus deferens) is
the channel by which the sperm are transported from the epididymis to the
urethra during ejaculation. The Urethra is surrounded by the Penis and
they are responsible for transporting sperm to mare’s reproductive tract.
3. The Prepuce
(sheath) surrounds and protects the penis.
4. Other
internal sexual organs of importance are the accessory sex glands (Seminal
Vesicles, Bulbourethral gland, prostate gland and and
the ampulla) which add fluid volume and nourishment to the sperm cells.
(Pre-ejaculate, ejaculate, gel fraction, tail end fraction of a semen sample)
Erection and ejaculation are brought on by
psychic stimulation of the brain usually brought on by a mare in heat.
b. Penis engorges with
blood which causes a rigid penis with an increase in length of about 50%.
c. Ejaculation –
expulsion of semen from the penis. Ejaculation consists of about 10 pulsations
that occur at approximately one second intervals. About 75% of the total sperm
is present in the first three to four spurts of fluid.
Puberty (attain the ability to breed a
mare) usually occurs in the light breed horses of North America at about 18 to
24 months. Puberty refers only to the presence of aggressive sex drive and
ability to produce mature sperm. The stallion does not achieve full
reproductive maturity until about 4 years of age.
Testosterone
caused male sex characteristics include:
1. Increased muscling
of the neck, head, shoulder and back.
2. Closure
of growth plates of the long bones (epiphysis)
3. Onset
and maintenance of normal sex drive
4.
Sperm production
5. Sex
drive (libido) and aggressiveness. (flehman response – curling of the upper lip)
Sex
drive is an inherited trait that determines how quickly the stallion can be
trained for breeding shed procedures and also determines how stable his
behavior will be after training. The act of breeding, in contrast, is a trial
and error - learning process.
A stallion “teasing” a mare
The
individual sperm anatomy
i. Head, neck piece, mid piece, tail.
ii. Must be seen microscopically in the
equine to determine normal anatomy and motility. (Motility of bull semen can be
determined without a microscope)
We
will go into greater detail and study of sperm cell anatomy and physiology in the
lesson on Artificial Insemination.
QUIZ:
Please answer
the following questions and send the answers to Dr. Sales at jsales@horsecoursesonline.com
Be sure to include
your full name, lesson number and email address on all work.
1. List the stallion anatomical structures and
the function of each, beginning with the production of the sperm cell and
continuing as the sperm cell travels through the stallion‘s reproduction system
and ends up within the mare’s reproductive tract, during a normal breeding act.
Include all accessory structures associated
with the stallion reproductive tract.
2. What is the difference between the endocrine
and exocrine function of the testicle in the stallion?
3. One pound equals how many grams?
4. Name the
three main structures involved with the thermo-regulation process in the
stallion.
5. Name
four sex characteristics that are found in the stallion due to the male sex
hormone testosterone.