Equine Reproduction Flashcards
what is the female germ cell called?
ovum
where is the ovum produced and nurtured?
in the ovary
what does it mean when an ovum is ovulated?
it is released into the oviduct
how long does the ovum remain in the oviduct? where does it go after this?
until fertilization occurs; then passes into the uterus
where does the fetus develop?
in the uterus until parturition
upon parturition, describe the route the fetus takes (5)
through the cervix, vagina, vestibule, and vulva to the exterior of the mare and a hopefully healthy foal is born
what shape and size is the ovary?
kidney bean shapes; generally 60-80mm (3in) length, 25-40mm (1.5 in) wide, and 20-30mm (1 in) tall
where is the mare ovary usually in a nonpregnant mare?
generally located between the last rib and the tuber coxae
what is the tuber coxae?
the point of the hip
where is the ovary found in pregnant mares?
pulled down deeper into the abdomen due to weight of the enlarging uterine contents; pulls down further as pregnancy progresses
what 3 things affect the position of the ovary in mares?
- age of mare
- parity number (number of foals the mare has had)
- contents of the GI tract (more fiber shifts the tract around)
what fixes the repro tract to the body wall?
the broad ligaments
generally describe the broad ligaments
layers of serous membranes of the peritoneum that originate from the sub-lumbar region (3-4 LV to 4SV)
what is the physical role of the broad ligaments?
hold ovary, uterus, and oviduct in place and position/support them
what is the functional role of the brtoad ligaments?
corridors for blood vessels, lympahtic vessels, and nerves
what are the 3 parts to the broad ligament? describe what they support
- mesovarium: supports ovaries
- mesometrium: supports uterus
- mesosalpinx: supports oviducts
what 4 structures are associated with an active ovary?
- follicles
- corpus hemorrhagicum
- corpus luteum
- corpus albicans
what is a follicle?
a fluid filled blister that develops on the surface of the ovary
what are the 2 purposes of the follicle?
- to protect and maintain the growing ovum
- to produce the excitatory hormone estrogen
what does estrogen do?
causes the mare to exhibit signs of estrus
what is the main difference between a horse and a humna ovary?
in humans, the cortex is on the outside and the medulla is on the inside, but in mares, the cortext is on the inside! and the medulla is on the outside
what happens to the follicle as it matures?
the follicle increases in size until it softens and finally ruptures, releasing the ovum (ovulation)
where does ovulation occur in a mare?
in a specialzed area of the ovary called the ovulation fossa
describe the average size of the ovary when ovulation occurs
between 40-45mm, but can be up to 51mm
once the ovum is released, what happens to it?
it is picked up by the fibriae of the infundibulum of the oviduct
what forms are the point of rupture as the follicle collapses during ovulation?
a small hemorrhage called the corpus hemorrhagicum
can you plapate the corpus hemorrhagicum? does it stick around for long?
no; it is difficult to palpate and short-lived for only 2-3 days
what does the corpus hemorrhagicum become after 2-3 days?
the corpus luteum
what is the corpus luteum? what does it do?
yellow body; produced progesterone
what does progesterone released by the corpus luteum do? (2)
- inhibits or stops the mare’s estrus behavior
- acts to maintain pregnancy
how long is progesterone produced from the corpus luteum if the mare is not pregnant? what happens to the CL after this amount of time if not pregnant?
corpus luteum will produce progesterone for about 12 days, then regress if the mare is not pregnant
if a mare is pregnant, how long will the CL be maintained and then what will happen to it?
CL will be maintained for approx 180 days before regression
since the CL is only maintained for approx 180 days of pregnancy, and a mare is pregnant for approx 340 days, what takes over to produce progesterone after the CL regresses?
the placenta
what happens as the CL regresses? (3)
- it is invaded by connective tissue that appears as white areas on the ovaries at the site of the CL
- the remaining scar is known as the corpus albicansm which serves no known function and disppears in approximately 6 months
if a mare is not producing enough of her own progesterone, what can be given? what are the drawbacks with this?
can give regumate, a synthetic progesterone, but it is expensive and must be handled incredibly carefully, especially by women, as it can absorb through the skin and mess with human cycling
why would a mare who must be given regumate to maintain her pregnancy continue to be bred?
if she has great genetics
what is the oviduct called in humans?
fallopian tube
in mares where is the oviduct located?
extends from the ovulation ofssa of ovary to the uterus
describe the oviduct in mares
a tortuous (twisty) tube 20-30cm (8-12in) long
what is the function of the oviduct? (2)
- site of fertilization
- carries fertilized ovum to uterus
what are the 3 parts of the oviduct?
- infundibulum
- ampulla
- isthmus
describe the infundibulum (2)
- portion that is in contact with the ovary (beginning of the oviduct)
- funnel shaped to accept the ovum
what does the infundibulum contain to aid in its function of accepting the ovum and how do they work?
contains fibria that palpate the ovary at the time of ovulation and prevent loss of the ovum into the abdominal cavity
what does the ampulla do? (3)
- transports the ovum to the uterus
- allows time for the ovum to mature after ovulation
- site of fertilization os primary function; occurs are ampullary-isthmus junction
describe the isthmus (2)
- narrow and extremely toruous
- coils its juncture with the uterus
when does fertilization occur?
approx 4-8 hours after ovulation
how long after fertilization does it take the fertilized ovum to travel through the oviduct to the uterus and why?
takes about 5 days after fertilization; this is because the oviduct is so twisty to slow the progress to allow maturation of the fertilized ovum before it enters the uterus
describe the mare uterus
bicornuate; composed of 2 uterine horns and the body that are connected almost perpendicularly to form a T or Y shaped configuration
describe the length of the horns and body of the mare uterus
both about 8-10 inches long (horns closer to 10 inches)
what does the size of a mare uterus depend on? (3)
- age
- parity
- size of mare
describe how the uterus sits in the mare’s body
the body lies at a slightly downward angle while the horns extend upward to the ovaries
describe the mare cervix (3)
- separates the uterus from the vagina
- tapers gradually into the uterus and extends out into the vagina
- controls the entrance of materials into the uterus
describe the cervix when a mare is in heat (2)
- cervix is dilated
- produces a thin, wtaery mucus that allows semen to enter the uterus
describe the cervix when a mare is not in heat (diestrus) or pregnant)
- cervix is closed tightly to prevent contamination of infection of the uterus
- firm upon palpation
describe the mare vagina (2)
- smooth muscle, tubular structure connecting the cervix and vulva
- serves as a passageway for the foal at birth and receives the penis during copulation
describe the vuvla of the mare (2)
- external protion of the mare’s repro tract
- lips of the vulva contain contractor muscles which help keep the opening closed to prevent feces or other foreign matter from entering
describe vulva lips when a mare is in heat (3)
- swell up
- become moist
- relaxed
what happens to the vulva lips of some mares known as windsuckers
some lips lose their tone and become loose and pliable (known as a pneumovagina) and can aspirate air and foreign matter into the vagina, causing uterine infection to occur
what is done to help mares that develop a pneumovagina?
a caslick operation is performed; lips are sutured together, leaving a small opening at the bottom for urination (these stiches must be removed prior to breeding or foaling though)
what kind of breeders are mares?
seasonally polyestrous; have heat periods running from early spring through late summer/early fall
what is mare reproductive activity patterned around?
daylight length; as daylight increases, mares start cycling and ovulating
when do mares reach peak repro activity? and when are they least active?
reach peak on June 22 (longest day of the year) and least active on December 22 (shortest day)
why do mares become reproductively active in spring and early summer/fall?
since their gestation is almost a year, they will in theory have the foal during warmer months when there is good grass for mom to make more nutritious milk and the foal won’t be as cold in the first bit of life
describe the anestrous period (3)
- mares show no sign of reproductive activity
- ovaries are small and inactive
- time of quiescence (dormant)
when do mares usually show signs of estrus without artificial lighting?
March, then more in April, with ideal breeding times in May and June
when do regular ovulations for mares begin? describe early heats before this
regular ovulations usually do not begin until about 30 days after the first estrus period; early heats are erratic and unpredictable
what may happen the first time a mare comes into estrus after her dormant period?
she may go through a silent heat; where she is in heat without showing obvious signs
is it wise to breed a mare right when she begins cycling after her dormant period? why or why not?
no; since so erratic or could have silent estrus, may waste money if try to breed before regular ovulations begin about 30 days after the first estrus period
what is the change from inactive to active reproductivity called in mares
transitional period
describe follicles during a mares transitional period and what this means for breeding
may develop, grow, and regress without ovulating; do not try to breed these; she may not even shows signs of estrus behavior
once a mare has settled into her breeding season (after her transitional period), how long is her normal estrous cycle?
21-22 days
how long does estrus average for a mare settled into her breeding season? but what is the range? when does ovulation occur with respect to the estrus period?
average is 5 days, but can range from 2-12 days; ovulation occurs 24-48 hours after the end of the estrus period
what is diestrus for mares?
the perios during the estrous cycle when the mare is not receptive to the stallion (she is not in heat)
contrast diestrus to anestrous
diestrus occurs while the mare is cycling, just not in heat, while anestrous is a period of no reproductive activity; no cycling at all
if conception does not occur, how long does diestrus last?
about 14-15 days
due to the estrous cycle lasting 21-22 days, about how many opportunities do you have to breed a mare?
only 4-5 cycles to breed in April to July
what is the advantage of having foals born as close to january 1st as possible?
all horses born in a given year are considered yearlings by january 1st of the following year; so foals born closer to january 1st will be more mature and developed than thhose who are born later
what can be used to induce the photo period in mares and get them to start cycling earlier than normal?
artificial lighting
describe how artificial lighting is used to induce mares to start cycling earlier than normal
16 hours of light and 8 hours of dark; but the program must be started 60-90 days in advance of when you want the mare to be breedable
if you want to breed a mare if feb/march, when should you begin artificial lights?
around December 10-15
if you want your foal to be born january 1st or near to it, when should you begin artificial lights?
in november
what is the minimum amount of light necessary to illicit the response of inducing cyclicity in mares? give old timey way and then modern way
- 10-12 foot candles of light
- 200 watt bulb
what is a good rule of thumb to ensure that the amount of artificial light you are using is enough to begin inducing cyclicity in your mare?
if you can read a newspaper in the corner of the stall/pen, then the light is sufficient
what can exposure of pregnant mares to extended light for a minimum of 70 days during the last trimester do?
shorten gestation length by 10 days
once mares are placed under artificial lights, can they be taken off of the 16 hours on program? what would happen if so?
no; not until 16hr of daylight naturally occurs, or the mare may lose the foal or stop cycling because she perceives the onset of winter
how does light generate cyclicity?
alters GnRH production indirectly through the pineal gland
how is melatonin made in the pineal gland?
tryptophan is converted to seratonin which is converted to melatonin
how is melatonin regulated in mares? give external and internal
externally by photo period
internally by hormonal feedback
how does light get to the pineal gland?
light receptors in the eye relay changes in the length of daylight to the pineal gland
what happens to melatonin production as daylight decreases?
melatonin synthesis and secretion from the pineal gland increases
when is more melatonin produced in mares? what is the result of this?
more melatonin is secreted when it is darker/less daylight, so more is secreted beginning is september/october, which shuts down the mare’s repro activity
describe the process of light traveling along nerve tracts from the retina to the pineal gland (4)
- retina is stimulated by light, which travels along a nerve tract to
- an area of the hypothalamus called the suprachiasmatic nucleus
- then, via another nerve tract, light travels to superior cervical ganglion and then
- along more nerve tracts to the pineal glad
what does increased light do to the inhibitory pathway of melatonin production and what is the result?
increased light stimulates the inhibitory pathway to decrease melatonin production
what happens to the inhibitory pathway of melatonin production during dark hours?
inhibitory pathway is reduced and melatonin production is increased
what are ganglion?
a group of nerve cells bodies
what is the hypothalamus referred to as?
the master organ of the brain
