The Reproductive System of the Mare
- the mare's reproductive organs are supported by the broad
ligament
- the main organs of the female reproductive system are the
ovaries, oviducts, and uterus
- the ovaries are the gonads of the female animal, and
there are two of them in each animal
- the two main functions of the ovary are the production of
eggs (ova) and hormones
- each ovary is kidney shaped, with a length of two inches
and a width of an inch and a half
- developing ovum are surrounded by follicles
- when the follicle bursts, ovulation occurs
- ovulation refers to the release of the egg by the ovary
- oviducts carry the egg from the ovary to the uterus, and
are the sight of fertilization if it is to occur
- the oviduct is 8 - 12 inches long
- the oviduct may also be called the fallopian tube
- the uterus, or womb, is where the unborn fetus grows
- the uterus may be divided into the uterine body, the
right horn, and the left horn
- the three layers of the uterine wall are the serous
membrane, the myometrium, and the endometrium
- the uterus and birth canal join at the cervix
- an ovum = an egg, the plural is ova
- fertilization refers to the union of the egg and sperm
- the period between fertilization and parturition is
called gestation
- in the mare, gestation lasts about 340 days
- gestation lasts longer in the jenny (female donkey)
- immediately after fertilization, the offspring is known
as a zygote
- after 6 - 8 days, the zygote implants itself on the
uterine wall, in either the right or left horn, and it is
an embryo; after the first trimester it is called a fetus
- parturition = birth
- the placenta is the structure which surrounds the unborn
fetus, through which nutrients and oxygen are passed from
the dam (mother)
- the three layers of the placenta are the allantois,
amnion, and chorion
- after birth, the mare nourishes her foal with milk
- the mammary glands of the mare are found in the udder
- lactation means the production of milk
- colostrum is the antibody rich first milk of the mare,
which provides passive immunity to the foal
- mastitis is a swelling of the udder
The Reproductive System of the Stallion
- the testicles, or testes, are the gonads of the male
animal, and are the primary organs of the stallion's
reproductive tract
- the testes produce hormones and sperm cells
- sperm cells, or spermatozoa, are the male sex cells
- in the male fetus, the testes are located on the upper
abdominal wall
- soon after birth, the testes drop down through the
inguinal ring and into the scrotum
- if only one teste drops into the scrotum, and the other
is permanently retained, the horse is referred to as a
cryptorchid
- the normal adult stallion has two testes located in the
scrotum
- the testes are suspended from the abdomen by the
spermatic cord, which also contains nerves and blood
vessels
- the blood vessels in the spermatic cord are arranged so
that the blood is cooled before it reaches the testes,
since heat inhibits sperm production
- the muscles in the spermatic cord and scrotum control
testicular temperature by positioning the testes close to
the body in cold weather and farther away when they are
warm
- the muscles within the spermatic cord are called the
cremaster muscles
- the muscles within the scrotum are called the tunica
dartos muscles
- the tissue which separates the two testes is the septum
scroti
- each teste is surrounded by a fibrous capsule called the
tunica albuginea
- each teste is divided into several lobules called lobuli
testis
- within each lobuli testis are the seminiferous tubules,
which contain the primary germ cells, which are
eventually to become viable spermatozoa
- Sperm production (spermatogenesis):
- the change from germ cell to spermatid
(immature sperm cell) lasts about 60 days
- begins in the seminiferous tubules, where
germ cells reproduce by meiosis, or sex
cell division
- an immature spermatid migrates from the
seminiferous tubules to the epididymis
- as the spermatid migrates it gains
maturity, losing cytoplasm and gaining a
tail, or flagellum
- final maturation occurs within the
epididymis
- the epididymis is a long, U-shaped structure attached to
the top (long axis) of each teste
- while in the epididymis, sperm are nourished by the fluid
around them, and chemicals prevent them from moving their
flagellum while they mature, thus forcing energy
conservation
- the vas deferens, or ductus deferens, is the duct which
carries mature sperm from the epididymus to the urethra
- the accessory sex glands secrete seminal fluid into the
vas deferens, forming semen
- the accessory sex glands of the stallion are the seminal
vesticles, the ampulla, and the prostate gland
- the seminal vesticles, or vesicular glands, secrete a
large portion of acidic seminal fluid, which contains
high levels of protein and potassium
- the ampulla is the enlarged glandular portion of the vas
deferens, and secretes a large amount of fluid very
similar to that of the seminal vesticles
- the prostate gland produces alkaline fluid that contains
proteins, compounds that break up proteins, citric acid,
and zinc
- the bulbourethral glands produce a clear fluid that
flushes the urethra of urine and bacteria before
ejaculation
- semen, carrying sperm, exits the body through the urethra
- ejaculation is the forcing of semen from the body
- the urethra is found within the penis
- the male copulatory organ is the penis, which rests in
the sheath, or prepuce
- the path of a sperm cell:
- from the seminiferous tubules (within the testes)
- to
the epididymis
- to the vas deferens
- to the urethra
and out of the body
- geldings are not capable of reproduction