Male Reproductive System
Reproductive system include primary, secondary and accessory sex
organs. Primary sex organs include two testes which are normally
located in an external sac of skin called the scrotum. Secondary sex
organs include duct system, epididymis and the penis. The
penis is transversed by urethra, which is the common passage
for urine and semen. The accessory organs include prostate gland, a pair of seminal vesicles,
and a pair of Cowper’s glands or bulbo-urethral glands.
Scrotum is a two-lobed sac developed from the invagination of
inguinal skin to accommodate the testes. Although it is apparently
divided into two almost equal halves by the median vertical band,
the left half is slightly longer and more voluminous than the right
Main function of scrotum is to support and protect the
testes suspended by the spermatic cord in the scrotal sac. The
scrotum functions as a heat-regulating mechanism in the male. It
keeps the testicles 4-5°C below normal body temperature. This
lowered temperature is essential for sperm formation. The large
number of sebaceous and sweat glands on the scrotum help in lowering
the scrotal temperature. During the hot season, the thermoregulatory
action causes the tunica dartos muscle to relax, allowing the
scrotum to elongate, dropping the testes far from the heat of the
body. During the cold season, the scrotal muscle contracts,
retracting the scrotum and bringing the testes nearer to the body.
This thermoregulatory action, however, does not begin until the
animal approaches puberty.
testes are primary sex organs in the male. They are found in
pairs suspended in the scrotal sac by the spermatic cord outside the
abdominal cavity in the inguinal region. Each testis is an
independent unit, separated from the other in the scrotal sac. The
testes are firm and compact masses of parenchymatous tissue.
testes develop within the abdominal region near the kidneys. They
commence their descent from the abdomen into the scrotal pouches
during fetal development. Migration is normally completed by the
time of birth or soon after birth. Sometimes one or both of the testes may fail to descend into the scrotum during maturity. This
condition is known as unilateral or bilateral cryptorchidism.
Bulls affected by bilateral cryptorchidism are sterile. This
condition is thought to be an inherited trait, hence such bulls are
not selected for further breeding.
Testes consist of a mass of coiled tubes called seminiferous tubules
which produce spermatozoa from the germinal epithelial layer by a
series of cell divisions. The seminiferous tubules join to form the
rete testes in the mediastinum, and these, in turn, lead into a
dozen efferent ducts, the vasa efferentia, which finally converge at
the dorsal part of the mediastinum to form the beginning of the
main functions of the testes are production of viable, potentially
fertile spermatozoa, and androgens or male
hormone. Main sex hormone, testosterone, is secreted by the Leydig cells or
interstitial cells of the testes. The secretion of this hormone is
regulated by the luteinizing hormone of the anterior pituitary
gland. Testosterone is responsible for the development and
maintenance of the functions of the male reproductive tract,
secondary sex characteristics, and sexual behavior.
epididymis emerges from the joining of the vas efferentia at
the dorsal part of the testis. It is a very long single duct, highly
convoluted and appearing as a mass of tubes. It is comprised of
three parts: the caput epididymis (head), the corpus epididymis
(body), and the cauda epididymis (tail). The tail of the epididymis
opens into the vas deferens.
Throughout most of its length, the epididymal tube is lined with
secretary cells. Spermatozoa accumulate in the epididymis and mature
during their passage through it. In epididymis, spermatozoa
mature and become
able to move
spontaneously and fertilize the ovum (egg) when they come in contact
Deferens (Ductus Deferens):
The vas deferens is a tube emerging from the tail end of the
epididymis. It starts from the base of the testes, extends upward,
and in association with the spermatic cord runs through the inguinal
ring, where it separates itself from the arteries, veins, nerves,
and other cord tissues. (Spermetic cord consists of testicular
artery, testicular vein, testicular nerve, vas deference, lymphatic
and cremaster muscles). Vas deference passes through the abdominal
cavity towards the pelvis and finally empties into the urethra. The
lumen of the vas deferens is narrow and lined with mucous membrane.
The wall is made up of longitudinal and circular layers of
involuntary muscles covered by the outer layer of the peritoneum.
The muscles of the vas deferens contract involuntarily during
ejaculation of semen and help in the expulsion of spermatozoa. In
the pelvic region, the vas deferens enlarges to form the ampulla of
Henle. The ampulla has numerous glands, and spermatozoa often
accumulate here before ejaculation. The glands of the ampulla
secrete fructose and citric acid which provide nutrition for the
The urethra is the common passage for the excretion of urine and
semen. It extends through the pelvis and the penis and ends at the
tip of the glans penis as the external urethral orifice. In the
urethra, spermatozoa mix with the seminal plasma of the accessory
sex fluids at the time of ejaculation.
The penis is essentially composed of erectile tissue. It is divided
into three portions: the attached portion is called the root, the
main portion is called the body, and the free portion is called the
glans penis. The erectile tissue is a sponge-like system of blood
vessels which becomes filled with blood under pressure when the bull
is sexually stimulated. This helps the penis to enlarge and become
rigid, thus enabling it to enter into the vagina of the female.
The penis of the bull contains very little
erectile tissue. The penis is a cylindrical organ with a tapering
end; the tapering portion opens at the angular end of the triangular
sheath. When the bull is not sexually excited, the penis is in an
'S'-shaped form known as a sigmoid flexure. During erection, the
longitudinal flexure straightens, thereby increasing the length of
the organ. The erector muscle
pulls the penis against the pelvis and aids in erection by
compressing the veins of the penis. The retractor muscles help to
return the extended penis to the flexed state.
Accessory Sex Glands:
The accessory sex glands of the male reproductive system are a pair
of seminal vesicles, the prostate gland, and Cowper's glands or
bulbo-urethral glands. They provide the bulk of the seminal
Seminal Vesicles -
Each of the two seminal vesicles are located on either side
of the ampulla. The seminal vesicles are lobulated and highly
secretary. They open either above or below the opening of the
vas deferens. The secretion of the seminal vesicles contains a large
amount of fructose and citric acid, which are required for the
nourishment of spermatozoa.
Prostate Gland -
The body of the prostate is situated in front of the seminal
vesicles on the dorsal surface of the pelvic urethra near the neck
of the urinary bladder. It secretes a mineral-rich fluid.
Cowper's Glands or Bulbo-urethral Glands -
The Cowper's glands are two in number and lie one on each side of
the pelvic urethra, partially buried in the transverse-cavernous
muscle. They produce a viscid, mucous-like lubricating substance.
Female Reproductive System
The female not only contributes the female sex cell (ovum) but also
provides the necessary environment in which the fetus is nourished.
These functions are performed by the primary and secondary organs of
the reproductive system. A pair of ovaries are the primary organs of
reproduction and produce not only ova but also the hormones required
for the normal sexual behavior of females. The secondary organs of
reproduction are a pair of oviducts (Fallopian tubes), the uterus,
the cervix, the vagina, and the vulva. The mammary glands are
also considered accessory sex organs as they are closely related to
the completion of reproduction by the nourishment of the young one.
The development of the reproductive organs starts before birth
during the embryonic stage, but they remain quiescent. After birth,
the reproductive organs develop gradually until the female attains a
specific weight at a certain age when she becomes sexually mature,
i.e. capable of producing viable gametes. The age at which a female
becomes sexually mature is called puberty.
There is a pair of ovaries. These are source of ovum which is
produced through the process of oogenesis and ovulation. These are
also concerned with production of ovarian hormones as estrogen,
progesterone and relaxin. Ovary is supported dorsolaterally by broad
ligament and medially by proper ligament. Size, shape and location
of ovary vary with species, stage of estrus and stage of gestation.
Oviduct or Fallopian Tube:
The oviduct is a tortuous, tubular structure of muscular and
epithelial tissues. It reaches from the ovaries to the tapered end
of the uterine horn. The oviduct consists of three parts: the
isthmus or narrow portion which adjoins the uterine horns; the
ampulla, which is slightly wider; and the infundibulum, which opens
into the peritoneal cavity.
The uterus consists of a body and two horns. It is a muscular and
irregularly tubular organ, the size of which increases during
It is sphincter like segment of reproductive tract which
anatomically and physiologically separates the uterine lumen from
vagina. Externally it has thick wall and internally has constricted
lumen. Function is to close uterine lumen against micro and
macroscopic intruders. It remains close at all the time except
during estrus and at the time of parturition. At estrus cervix
serves as passage way for sperm. In pregnancy the cervical mucous
hardens and seals off the canal by forming cervical plug and
cervical seal which liquefy shortly before parturition. At
parturition cervix dilates and allows passage to fetus and fetal
The thin but elastic-walled tubular connection of the cervix with
the vulva is called the vagina. It is a common passage for the
reproductive and the urinary tract. The epithelial lining of the
vagina undergoes changes during the estrus cycle.
The external opening of the female genitalia is called the vulva. It
includes the clitoris and the vestibule. The clitoris is a structure
of erectile tissue (homologous with the male penis) located just
inside the lower junction of the vulvular lips. The external
opening of the reproductive tract of the cow lies just below the
anus. The thick labia majora are covered with fine hair.
It is located between vulva and vagina and is comprised of two
labia. The dorsal and ventral comissure and clitoris form the caudal
termination of genital tract. Urethra opens into cranial ventral
portion of vestibule. Vestibule has several circular or sphincter
like muscles that close the genital canal to the outside. These
muscles attach to the perinial body, the sphincter muscle of anus
and caudal and last sacral vertebrae. Just during parturition the
vestibule acts as the point of attachment of the entire genital
tract to contract when expelling the fetus.
Puberty in Females
Puberty is the age when animal attains the
ability to release the gametes and manifest complete sexual
behavioral sequences. Puberty age is very important parameter for
the successful livestock farming. Those animals which attain puberty
earlier give more production.
Factors affecting Puberty in Females:
Genetic makeup of the animal - Exotic breeds attain puberty
earlier as compared to local breeds. Exotic dairy breeds attain
Puberty in 12 – 15 months. Exotic Beef breeds attain puberty in 15 –
18 months. Local breeds attain puberty at the age of 18 – 24 months.
Nutrition - In underfed animals, puberty is delayed. On
balanced diet puberty is attained earlier. When the animal gains 55
– 60% of adult body weight, then animal attains puberty.
Temperature - In summer the temperature is very high, due to
heat stress growth rate is low and puberty is delayed.
Management - When males and females are kept together then
puberty comes earlier and vice versa. It is due to sight and