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.