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2
testes
o Attached epididymus
2
ducts
 Urethra
 Penis
 Accessory Sex glands
o Bulbourethral
o Prostate
o Vesicular
Can
be considered “master organ”
o Site for production of spermatozoa
(spermatogenesis)
o Production of Testosterone
As
testicular size increases
o Ability to produce spermatozoa increases
Size
also increase until age 12-13
 Function
of the testes starts with the hypothalamus
 Release of GnRH from hypothalamus to the
pituitary gland
o Stimulates production of FSH, and LH
• FSH  effects sertoli cells
•
•
•
•
Sertoli Cells located in the testes epithelium
Support spermatozoa development
Secrete protein which regulate FSH
Also proteins that bind testosterone
• LH effects leydig cells
• Located between seminiferous tubules
• Responsible for testosterone production
• Also secrete estrogen
 Concentrations
control release of GnRH
through a negative feedback system
o Testosterone
, system will slow down
testosterone due to inhibition of the
hypothalamus and pituitary gland
o Testosterone , there is no inhibition and
system testosterone
 Levels
reduced when given anabolic steroids
o Stallion displays normal behavior, but testicular
size and sperm production are impaired

When daylight periods are short
o Pineal Gland (located in the brain) releases melatonin
• Thought to inhibit hypothalamus from release GnRH
• Therefore inhibits LH and testosterone

Winter months male reproduction is suppressed
o Testicular size and sperm count is reduced
o Low sex drive (libido)

Can be placed under lights to increase testicular activity
o Normally exposed to 16 hours of daylight beginning in December
o Testicular size and sperm production will approach normal in approx
60 days

Spermatogenesis occurs in the seminiferous
epithelium
o Maintains population of uncommitted germ cells which future
spermatozoa can be produced
o Results in the formation of germ cells (spermatogonia) which
give rise to spermatozoa

Entire process divided into 3 stages
o Spermatocytogenesis
o Meiosis
o Spermiogenesis
o Each phase requires 18-19 days
o Entire process requires 57 days

Once spermatozoa are released
o Travels through ducts to the epididymus
• Lightly attached to the testes

Epididymus divided into 3 segments
o Head (caput)
o Body (corpus)
o Tail (cauda)

Within epididymus
o Sperm undergo maturation
• Acquire ability to swim and fertilize an egg
o Migration take approx 8 days
o Stored in the tail of the epididymis until ejaculation

Total length 65 days
 Daily
Sperm Output (DSP)
o # of spermatozoa produced within 24 hour
o Vary among stallions and testicular size
o Determined by collecting stallion for 7 days
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
Testes are suspended with the scrotum by the spermatic
cord and associated with the cremaster muscle
Scrotum is a pendulous sac that maintains temperature for
sperm production
Tunica dartos and cremaster contract during cool weather
and drop away to lower temperature
Elevated temperature will result in lower spermatozoa
A decrease in fertility may not be seen for about 2 months
 Classified
as a musculocavernous type
o Consists of:
• Root
• Attached the penis to the skeleton
• Main body (shaft)
• Glans penis
• Free end of the penis

Spermatozoa released from the tail of the epididymus
o Moved via muscular contraction through the ductus deferens in the pelvic
urethra
o Mixed with secretions of the accessory glands during ejaculation
• Referred to as semen

Seminal fluid
o Fluid portion of semen
o Consists of testicular, epididymal, and accessory sex gland secretions

Released in fractions
o First: pre-sperm
• Cleans urethra
o Second: sperm-rich
• 45% of ejaculate volume
• 75% spermatazoa
o Third: sperm-poor
• Contain gel, filtered out during sperm collection for AI

http://peer.tamu.edu/video/videovettech/equine_reproduc
tion.m4v