Stallion-Reproductive Anatomy Flashcards
what does a stallion’s reproductive organs consist of? (6)
- 2 testes
- scrotum
- epididymis
- two ductus deferens
- accessory sex glands
- penis
what is each testis suspended by? (2)
spermatic chors and external cremaster muscle
what are the 3 accessory sex glands?
- paired vesicular glands/seminal vesicles
- one prostate gland
- paired bulbourethral/cowper’s glands
why are the testes held outside the body cavity?
so that the sperm can be held at cooler-then-body temperature in order to not kill sperm
what is the function of the bulbourethral/cowpers glands? (2)
- contribute gel fraction of ejaculate
- causes seminal plasma to coagulate following ejaculation
what is the function of the testes? (2)
- production of spermatozoa
- production of androgens
what is the function of the scrotum? (3)
- support the testes
- temperature control of the testes
- protection of the testes
what is the function of the spermatic chord (2)?
- support the testes
- temperature control of testes
what is the function of the epididymis? (4)
- concentration of spermatozoa
- storage of spermatozoa
- maturation of spermatozoa
- transport of spermatozoa
what is the function of the vas deferens?
trnasport of spermatozoa
what is the function of the urethra?
transport of semen
what is the function of the vesicular glands/seminal vesicles?
contributes fluid, energy substrates, and buffers to semen
what is the function of the prostate gland?
contributes fluid and inorganic ions to semen
what is the function of the penis?
male organ of copulation
what is the scrotum?
an outpouching of the skin, divided into 2 sacs
what does each sac of the scrotum contain, located where?
a testis, located on either side of the penis
where should testes descend and when?
from the abdominal cavity through the inguinalcanal into the scrotum, during the last 3 weeks of gestation up to the first two weeks after birth
at what point should you get worried if your colt’s testes haven’t descended?
if you can’t palpate them at 18months, be worried; then act if can’t feel by 2 years old
what is the temperature of the testes? compare to body temp
testes: 30.5-32.5C or 86.9-90.5F
body: 38C or 100F
what is a cryptorchod testis?
one that stays in the abdomina cavity or inguinal canal
what are the 2 major functions of the male reproductive organs?
- produce testosterone to allow sperm production
- produce, store, and deliver mature viable sperm
where does sperm production begin?
with the seminiferous tubules of the testes
where does sperm production end?
with the urethral orifice of the penis
where are spermatozoa produced and begin to mature?
in the seminiferous tubules of the testes
after spermatozoa are formed where do they go? give general and then the next 4 places in the path after leaving seminiferous tubules
pass through remaining tubules of the testes
1. seminiferous tubules
2. straight tubules
3. rete tubules
4. efferent tubules/ductules
5. then reach the duct of the head of the epididymis
what is the epididymis made up of?
head (caput), body (corpus), tail (cauda)
what happens in the epididymis?
final maturation of spermatozoa into motile, viable sperm
where are mature sperm stored and until when?
mature sperm stored in the tail of the epididymis until ejaculation
how long is spermatogenesis in the stallion from start to finish?
57-58 days
what happens to sperm shortly before ejaculation?
they are carried to the pelvic urethra from the epidiymis by the ductus deferens
what happens as sperm reach the pelvic urethra before ejaculation?
they are mixed with seminal fluid and secretions from the accessory sex glands
what do the secretions of the accessory sex glands do? (3)
- provide required nutrition (energy and protein) for the sperm
- act as a buffer
- prepare the lumen of the pelvic urethra for favorable passage of the sperm (lubricant)
what makes up the majority of the ejaculate volume?
the seminal plasma
what is the proposed function of seminal plasma? what is the known drawback?
appears to be important to sperm function, but long-term exposure to seminal plasma components may be detrimental to sperm survival of some stallions
in fresh or chilled programs, what happens to plasma?
it is diluted with extenders
what is done to remove seminal plasma in frozen semen?
centrifugation; will get a sperm pellet once you remove the supernatant
what kind of response do all mares have to frozen semen?
some level of inflammatory response
list the 5 aspects of neuroendocrine control of stallions
- hypothalamus
- pituitary gland
- pineal gland
- testes
- vomeronasal organ
what causes the hypothalamus to release GnRH in the stallion?
response to neural and hormonal inputs
what is the vomeronasal organ? what is it also called? describe and give its location
also called the Jacobson’s organ; is an accessory olfactory organ that is a duct lying beneath the nasal mucosa
what is the vomeronasal organ connected to?
connected to 2 small openings in the anterior roof of the mouth just behind the upper lip
how do chemicals enter the vomeronasal duct? what happens next?
through the oral cavity by the nasopalaitne ducts, that lead to the vomeronasal organ, where sensory neurons in the vomeronasal organ evaluate the material aspirated
describe the flehman response in stallions (3)
- direct air across the openings conveys olfactory information from pheromones to the hypothalamus
- this causes GnRH to act on the anterior pituitary, which regulates production and release of LH and FSH
- these gonadotropins act on cells of the testes, regulating spermatogenesis and steriodogenesis
what is the source of the pheromones that cause stallions to exhibit the flehmen response?
estrogen is released in the urine when a mare in heat urinates as an estrus behavior
are stallions the only animals that can exhibit the flehman response? if not, provide 4 others
no;
1. mares and foals
2. cats
3. dogs (esp bloodhounds)
4. cows
what does FSH do in stallions?
regulates compounds produced by sertoli cells, which are nurse cells that are important in sperm production
what does LH do in stallions?
regulates the Leydig cells of the testes, stimulating production of testosterone and estrogen
what is testosterone mainly important for?
normal spermatogenesis
give 3 functions other than normal spermatogenesis that testosterone is important for
- maintaining accessory sex organs
- development of secondary sex characteristics of stallion
- maintain libido
give 2 examples of secondary sex characteristics in stallions
- they are more muscular
- thick neck (cresty neck)
what does estrogen do in stallions?
may also function in maintenance of accessory sex gland function and libido via feedback on the hypothalamus and anterior pituitary gland to regulate LH release
how can you tell a cryptorchid without ever palpating it?
cryptorchids have the highest estrogen levels of any make horse! this can help you tell if that “gelding” actually has a retained testicle
is the photoperiod important to a stallion? compare to mare
yes, but the importance of the pineal gland and influence of season is less obvious in stallions than mares, since stallions produce sperm throughout the year
describe when the max values of testicular size, semen production, libido, and hormone concentrations are observed in stallions
in spring and summer, or May-July, which is also the peak period of cyclicity for mares
describe stallion repro activity in December-February (2)
- spermatozoal output is 50% of peak
- volume ejaculated is 50% of peak
what does exposure of stallions to 16 hours of artificial light and 8 hours of dark do intially? then after a while?
results in early attainment of peak production, but prologned exposure to artificially long days does not maintain peak production, as these stallions will experience a photorefractory period and display earlier than normal regression of testicular size
at least how old must a stallion be before he is producing viable sperm to be bred?
at least one year old
when do some start sparingly breeding a stallion and why?
at 2 years old but only if has great genetics and conformation, as is not old enough to have proved himself as great in any other way yet
what is the risk in breeding a young stallion live cover? (2)
- may be savaged by mares
- may start to savage mares himself
when are most stallions put into full service?
at four years old
how many mares can a 2 year old stallion breed per season?
6/7
describe the breeding schedule of a three year old stallion
either 4-6 services/week or 12 mares/season
describe the breeding schedule of a mature stallion
serviced daily for 7-8 days a week with one day off, or twice daily, 3-4 days in a row
