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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 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

 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

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