ANIMAL REPRODUCTION

1. Animal Reproductive System
THE reproductive system is the only sys-
tem in animals that is different
between genders. Breeders and others in
the animal industry need a thorough under-
standing of the female and male reproduc-
tive tracts.
Objective:
þ Explain the functions of the female reproductive tract and the male reproductive
tract.
Key Terms:
Ñ accessory glands
cervix
clitoris
Cowper’s gland
ejaculation
fallopian tubes
infundibulum
ovary
oviducts
penis
prostate gland
scrotum
testicle
testosterone
urethra
uterus
vulva
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2. Female Reproductive Tract
The reproductive system of the female produces egg cells, is the site of fertilization, and
develops the fetus. Its structures are significantly different from those of the male reproductive
system.
The vulva is the external opening of the female reproductive and urinary tracts. Inside the
vulva is the clitoris, which is the sensory organ of the female. Anterior to the vulva is the
vagina. The act of copulation, or mating, occurs in the vagina. During natural mating, semen
from the male is deposited in the vagina. The vagina is part of the birth canal. The fetus passes
through the vagina during birth.
The cervix is a muscular structure between the vagina and the uterus. The annular rings
and gel-like mucus substance seal the uterus during pregnancy to protect the developing fetus
from infection. During birth, hormones cause the cervix to relax, allowing the young to pass
through.
The uterus is the location where the embryo develops. The uterus is a Y-shaped structure
with two uterine horns. The size of the uterine horns is dependent upon the typical number of
offspring produced in one pregnancy. An animal such as the horse that usually has only one
offspring per pregnancy has small uterine horns and a large uterine body. An animal such as
the pig that has large litters has large uterine horns and a small uterine body.
The oviducts, or fallopian tubes, are tubular structures that connect the ovaries and the
uterus. The reproductive tract has two oviducts, one joining each ovary to a uterine horn. The
union of the sperm and the egg cell occurs in one of the oviducts. The resulting zygote travels
through the oviduct for implantation into the uterine wall. The infundibulum is the funnel-
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Cervix
Rectum
Vagina
Vulva
Bladder
Ovaries
Oviduct
Uterine
horns
FIGURE 1. Cow reproductive system.

3. shaped opening of the oviduct. As the ovary releases an egg cell, it is directed into the oviduct
by the infundibulum.
The ovary is the structure that produces the egg cell. It is also responsible for the produc-
tion of the hormone progesterone. Each female mammal has two ovaries. In some animals, like
chickens, only one ovary functions. Each ovary contains a predetermined number of follicles
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Rectum
Vagina
Vulva
Clitoris
Cervix
BladderOvaries
Infundibulum
Oviduct
Uterine horn
Uterine body
FIGURE 2. Sow reproductive system. (Courtesy, Gary Stegman, Crookston, MN)
Ovary
Follicles
Magnum
Vagina
Cloaca
Rectum
Rudiment of oviduct
Intestine
Mature ovum
Infudibulum
Isthmus
Uterus (shell gland)
FIGURE 3. Hen reproductive system. (Courtesy, Gary Stegman, Crookston, MN)

4. when the animal is born or hatched. For instance, a female chick normally has around 4,000
immature follicles, while a heifer has 75,000 immature follicles.
Male Reproductive Tract
The reproductive system of the male produces and stores semen and deposits it into the
female reproductive tract.
The penis is the organ that deposits semen, the fluid containing sperm cells, in the female
reproductive tract. During copulation, the natural act of mating, ejaculation occurs, expel-
ling the semen. The end of the penis serves as the sensory organ, which stimulates ejaculation.
The penis is normally relaxed and housed in a protective sheath. However, when stimulated,
the retractor muscle relaxes, and the sigmoid flexure allows the penis to extend from the
sheath. The penises of different species are physiologically different. The penis of the stallion
contains erectile tissue, while the penises of most other species do not. The boar has a uniquely
shaped penis that resembles a corkscrew but fits the sow’s reproductive tract perfectly. The
urethra is the tube that extends through the penis and allows for the excretion of urine. A
male fowl has no penis; instead, it has an undeveloped copulatory organ to deposit semen in
the oviduct of the hen. A fish expels semen through the urogenital pore.
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Cowper’s gland
Spermatic cords
Sheath, laid open
Prostate gland
Seminal
vesicles
Penis
Ureters
Bladder
Vas deferens
Testicles
Scrotum
Tail
Body
Head
Epididymis
Sigmoid
flexure
FIGURE 4. Bull reproductive system.

5. The accessory glands produce fluids that benefit the sperm cells. The Cowper’s
gland creates a fluid that cleans and neutralizes the urethra prior to ejaculation. The pros-
tate gland secretes a fluid that provides the transportation medium for sperm. A fluid
secreted by the seminal vesicles provides nourishment for the sperm.
The testicle produces the male gametes and the male hormone testosterone. The two
testicles of a male mammal are held in the scrotum, while in fish and poultry the testicles are
held internally. Cryptorchidism is the condition in which one or both of a mammal’s testicles
do not descend into the scrotum but are instead held in the body cavity. This causes sterility in
the affected testicle(s). In a mammal, the scrotum is necessary to provide an environment that
encourages sperm production, since its temperature is slightly below the body temperature of
the animal.
Summary:
2 The female reproductive tract includes the vulva, vagina, cervix, uterus, fallopian
tubes, and ovaries. The male reproductive tract includes the penis, urethra, acces-
sory glands, testicles, and scrotum. Copulation is the natural act of mating.
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Cowper’s gland
Retractor penis
muscle
Epididymis
Scrotum
Testes
Vesicular glands
Prostate gland
Rectum
Ampulla
Vas deferens
Bladder
Ureter
Glans penis
Sheath
FIGURE 5. Stallion reproductive system. (Courtesy, Gary Stegman, Crookston, MN)

6. Checking Your Knowledge:
´ 1. List the structures of the female reproductive tract. Explain the function of
each.
2. List the structures of the male reproductive tract. Explain the function of each.
Expanding Your Knowledge:
L Interview a livestock producer. If you are unable to find one locally, check with a
livestock breed association to obtain the necessary contact. Determine from your
interview why a complete understanding of animal reproduction is important to the
producer’s success. Identify what combination of on-the-job experience and educa-
tional training contributed to the person’s overall knowledge of the subject.
Web Links:
: Reproduction in Farm Animals—Oklahoma State University
http://www.ansi.okstate.edu/course/3443/study/
Bird Reproductive System
http://www.birdsnways.com/wisdom/ww32eiv.htm
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