Male Reproductive Anatomy and Physiology
Lesson 1-Reproductive Anatomy of Bull
The primary reproductive organs of the bull consist of two Testes. The secondary organs
are Epididymis, Vas Deferens, and Penis, and the Accessory glands are Seminal Vesicles,
Ampullae, Prostrate Glands, and Cowper’s Gland. These organs work in concert for
formation, maturation and transport of spermatozoa
Figure: Reproductive organs of the bull. (Source: Bogart & Taylor, 1983)
Testis
Testes: are bean-shaped organs enclosed within a sac like structure called Scrotum or
Scrotal Sac. The testes comprised mainly of tiny tubules called Seminiferous Tubules,
which are lined, by germinal epithelium cells. These epithelial cells lining the
seminiferous tubule produces the male sex cells called Sperm or Spermatozoa that
fertilizes the eggs, or Ova, of the female. There are interstitial cells found in between the
seminiferous tubules. These cells are called the Leydig Cells, which secrete the male
hormone called the Testosterone. The testosterone conditions the male sexual
characteristics.
Semineferous tubule
Semineferous tubule enlarged
Testicle showing semineferous tubule
Scrotum: The scrotum is a two-lobed sac that contains and protects the two testicles. It
acts as a thermo-regulatory organ by regulating the temperature of the testicle,
maintaining them at a temperature lower than a body temperature. For example, it is 1.6
C to 3.9 C lower in the bull and 5 C to 7 C lower in ram and goat. When the
environmental temperature is low the tunica dartos muscles of the scrotum contracts,
drawing the testicle towards body and its warmth, and when the environmental
temperature is high, this muscle relaxes, permitting the testicles to drop away from the
body and its warmth. This heat-regulating mechanism of the scrotum begins at about the
time of puberty when the testicular hormones starts to function.
When the environment temperature is so hot that the testicles cannot cool sufficiently, the
formation of sperm is impeded and a temporary condition of lowered fertility is
produced. Therefore, providing shade for the male animals during hot day, cold water to
drink and at the same time providing cool air to breath over the cold water or even
providing air conditioning are ways to manage and prevent this temporary sterility.
Secondary Organs
Epididymis: It is a very long tube (30-35 m in the bull, longer in the boar & stallion)
held in a covering applied closely to the exterior to the testicles. It is the site of the site
where the sperm cells that enter from the seminiferous tubules get matured. The sperm
cells acquire more and more capacity to fertilize ova as they move through this tube.
According to the study, sperm taken from the part of the epididymis nearest the testicle
are not likely to be able to fertilize the ova, whereas those taken from areas farther along
this long, winding tube increasingly show the capacity to fertilize (Bogart & Taylor,
1983).
The sperm is moved to vas deferens. If not moved and not ejaculated, the sperm get
degenerated and absorbed in the part of the epididymis farthest from the testicle.
Ductus deferens: are essentially transportation tubes that carry the sperm-containing
fluid from each epididymis to the urethra. The vas deferens joins the urethra near its
origin as the urethra leaves the urinary bladder. In the mature bull, the vas deferens is
about 3 mm in diameter except in its upper part where it widens into a reservoir, or
ampulla, about 10 to 17 cm long and 1 cm wide. The ampulla of the vas deferens is
profusely supplied with nerves from the pelvic plexus of the sympathetic nervous system.
Under the excitement of anticipated mating, the secretion loaded with spermatozoa from
each epididymis is propelled into each vas deferens and accumulates in the ampulla of the
deferent ducts. This brief accumulation of semen in the ampulla is an essential part of
sexual arousal. The sperm reside briefly in the ampulla until the moment of ejaculation
when the contents of each ampulla are pressed out into the urethra and then through the
urethra and the penis en route to their deposition in the female tract.
Accessory glands
Seminal Vesicles:
Sizable organs found at the base of the urinary bladder and on either side of the pelvic
urethra opening into the urethra near the place where the deferens ducts open into it. In
the bull the seminal vesicles are about 10 cm long and 2.5 cm in diameter. The boar’s
seminal vesicle are large, thin-walled, pyramid-shaped glands in which the apex points
posteriorly. The combined weight of the two glands varies from 150-850g and the content
from 38 to more than 500g.
To the semen (the fluid that contains the sperm), the seminal vesicles contribute ascorbic
acid, citric acid, inorganic phosphorous, acid-soluble phosphorous, and the bulk of the
seminal fructose, and in the case of the boar, much ergothionine. Seminal vesicle are
prominent in the bull, stallion, ram, and goat, but are absent in the dog and cat.
Prostate Gland:
Prostrate gland is also found at the base of the urinary bladder and is composed of a
group of some twelve or more glandular tubes, each of which empties into the urethra,
also near the opening from the urinary bladder and dorsal to it.
In the bull the main part of the prostate is about 37 mm across (left to tight) and 12 mm in
diameter. Additional prostate tissue is scattered among the muscles of the pelvic urethra.
The prostate empties into the urethra through a small opening in the muscular wall of the
urethra. It supplies antiagglutin and minerals to semen plasma.
Bulbourethral Glands:
Sometimes referred to, as Cowper’s Glands, are located on either side of the pelvic
urethra, just posterior to the urethra-penis where the urethra-penis dips downwards in its
curve. The bulbourethral glands are covered by fibrous tissue. Except for the boar, they
are small in farm animals. In the bull, they are about 25 by 12 mm, but in the boar they
are comparable in shape and size to a banana (15 by 3 to 5 cm). The secretion from the
bulbourethral glands is thick and viscous, very slippery, or lubricating, and whitish in
colour. It has high sialoprotein content. This sialoprotein is involved in the formation of
the gelatinous fraction of the semen in the boar and probably in the stallion. The seminal
vesicles, prostate, and bulbourethral gland are known as the accessory sex glands. Their
primary functions are to add volume and nutrition to the sperm-rich fluid coming from
the epididymis.
Penis:
The penis is the organ of copulation. It also provides passageway for the escape of urine.
It is a muscular organ characterized especially by its spongy, erectile tissue that fills with
blood under considerable pressure during periods of sexual arousal, making the penis
rigid and erect. The penis in bull is about 1 m long and 3 cm in diameter, tapering to the
free end. In the bull, boar, and ram the penis is S-shaped when relaxed. This is S-curve or
sigmoid flexure, is eliminated when the penis is erect. The curve is restored after
copulation when a pair of retractor muscles draws the relaxing penis back into its sheath.
The stallion penis has no S-curve and it is enlarged by engorgement of blood in the
erectile tissues.
Triple role of Penis:
 Passage for urine
 Passage for products originating in other organs of reproduction
 Organ of copulation
The free end of penis is termed the glans penis.
All these accessory male sex organs depend on testosterone for their tone and normal
condition. This dependence is especially apparent when the testicles are taken away (as
castration); the usefulness of the accessory sex organs is then diminished or even
terminated.
Urethra
It is a large, muscular canal extending from the urinary bladder. The urethra runs
posteriorly though the pelvic girdle and curves downwards and forwards through the full
length of the penis. Very near the junction of the bladder the urethra, the tubes from the
seminal vesicles and the tubes from the prostate gland join this large canal. The
bulbourethral gland joins the urethral at the posterior floor of the pelvis. The urethra is
lined with many tiny glands whose watery secretion is clear and high in mucoproteins.