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VET 410: Reproduction > Equine Cyclicity > Flashcards

Equine Cyclicity Flashcards

1
Q

are horses seasonal or non seasonal breeders

A

seasonally polyestrous - long day (breed in spring/summer)

21 day cycle that repeats during season

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2
Q

seasonal transition period

A

the first cycle after entering the breeding season has an abnormally long estrus period with irregular inter-estrous intervals

NO ovulation occurs during this time (follicles will just regress) = infertile

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3
Q

what stages of the cycle do horses have

A
  1. estrus
  2. diestrus
  3. seasonal anestrus (enter when out of season)
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4
Q

estrus

A

“horsing”; female is receptive to the male

LONG - 6-7 days

high estradiol
low progesterone

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5
Q

how big are horse follicles

A

VERY large

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6
Q

when does ovulation occur in horses

A

before the end of estrus

mare can be bred and still be in estrus afterward due to long length of estrus

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7
Q

where does ovulation occur in the ovary

A

ovulation fossa only

cortex and medulla are inverted (medulla outside, cortex inside) and follicles ovulate from the cortex, so there is only one site that ovulation can occur at

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8
Q

can hormones can be used to induce ovulation in mares

A

GnRH or hCG

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9
Q

can horses super ovulate

A

NO because ovulation can only occur at the ovulation fossa and follicles are too large to ovulate multiple at a time

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10
Q

does double ovulation occur in mares

A

yes decently often, but mares can NOT support twins so they usually reduce to a single fetus

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11
Q

is the corpus luteum palpable in mares

A

no - does not expand from the outer surface

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12
Q

are the follicles palpable in mares

A

yes - large and extend from outer surface

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13
Q

diestrus

A

occurs after ovulation and estrus ends, no longer “horsing”

low estradiol
high progesterone

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14
Q

diestrus ovulation

A

second ovulation NOT associated with LH surge that occurs during the luteal phase (2-12 days after regular ovulation) despite high luteal progesterone

extends the length of the interestrus interval

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15
Q

is estradiol alone enough to induce estrus in horses

A

NO requires:
- high estradiol
- LOW progesterone (from luteolysis)

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16
Q

function of progesterone in horses

A

primes the next estrus
suppresses receptivity/ovulation

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17
Q

is luteolysis in horses spontaneous or senscent

A

spontaneous - relies on placental production of PGF2a and CL production of OT (+/+ feedback) to regress CL

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18
Q

is luteolysis in horses local or systemic

A

systemic - PGF2a released from one uterine horn CAN affect the contralateral ovary

NO vascular architecture to support local luteolysis

reduced metabolism of PGF2a in the lungs allows higher concentrations to reach both ovaries

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19
Q

do horses ovulate a primary or secondary oocyte

A

secondary oocyte - can be fertilized immediately after ovulation

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20
Q

do sperm have a long or short lifespan in the female repro tract

A

long BUT oocyte does not - still want sperm present at the time of ovulation

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21
Q

what is unique about unfertilized oocytes in horses

A

unfertilized oocytes will accumulate in the oviduct - do NOT get released into uterus

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22
Q

what hormone is used to facilitate the transport of fertilized embryo into the uterus

A

PGE2 secreted by the embryo

relaxes the oviduct papilla

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23
Q

embryonic capsule

A

blastocysts form a hard capsule within the zona pellucida before entering the uterus
- forms at day 6 and maintained even after embryo hatches zona pellucida
- maintains spherical shape to protect embryo during transplacental migration

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24
Q

transplacental migration

A

spherical, encapsulated embryos migrate extensively between uterine horns from day 11 to 16
- driven by PGE2 that is secreted by the embryo

NO elongation in uterine horns

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25
Q

is MRP in horses local or systemic

A

systemic - unknown signal from embryo will prevent PGF2a secretion from both uterine horns

26
Q

embryo fixation

A

embryos become fixed at the base of one uterine horn on day 16-17

remains in embryonic capsule until day 21

27
Q

what method is used to diagnose pregnancy in mares

A

ultrasound - embryos detectable by day 12-14
- twins detected by day 16
- recheck day 28

28
Q

why can an equine placenta not support twins

A

limited surface area/capacity for nutrient exchange

blood flow is HIGH enough to support twins, but need more surface area to allow nutrient exchange

29
Q

choriovitelline placenta

A

primary placenta formed by the yolk sac to sustain fetal development until the chorioallantoic placenta forms

fully vascularized

regresses day 35-40 once CA placenta forms

30
Q

how do hormone concentrations in pregnant mares vary from those in non-pregnant mares

A

do NOT differ until day 45-60 of gestation when estrone sulphate starts to increase in association with the development of the CA placenta and formation of endometrial cups

31
Q

endometrial cups

A

colonies of chorionic girdle cells (specialized trophoblasts) that form within the endometrium

maintains progesterone secretion during early pregnancy (before CA placenta)
- secrete eCG
- stimulates ovulation or luteinization of follicles to form a secondary CL

degenerates around day 60-70 and eCG levels drop to 0
- sloughs off and becomes allantoic pouches

32
Q

eCG

A

equine chorionic gonadotropin

heavily glycosylated LH that revives the corpus luteum as it starts to regress

33
Q

what is a useful pregnancy diagnostic in mares

A

estrone sulphate

increases exponentially after day 45 (associated with eCG and endometrial cups)

34
Q

luteo-placental shift

A

the shift of progesterone production from the CL to the placenta that occurs at day 110

once CA placenta develops - progesterone secretion is independent of the CL

35
Q

what species have placentas that can produce progesterone

A
  • horses
  • cows
  • sheep
  • cats
36
Q

what species rely on CL for progesterone secretion throughout entire pregnancy

A
  • dogs
  • pigs
  • goats
37
Q

what type of progesterone does the placenta produce

A

DHP - 5a reduced progesterone

38
Q

regumate

A

oral progestin that can be given in early pregnancy if in luteal failure

NOT needed after day 110 since CA placenta develops

androgenic - can cause early onset infertility in offspring

39
Q

fetoplacental unit

A

fetal gonads become the primary source of androgen secretion (DHEA)

DHEA gets converted into estrone sulphate and equine specific estrogens

40
Q

does the oogonial cap or interstitium of the ovary produce DHEA

A

interstitium - causes ovaries to become extremely large

interstitium will eventually regress and only oogonial cap will remain; DHEA production will drop

41
Q

what are the stages of structures that support progesterone secretion in mares

A
  1. CL
  2. endometrial cups (via eCG that saves the CL)
  3. chorioallantoic placenta
42
Q

when does DHP withdrawal occur in mares

A

2-3 days before parturition; caused by both decrease in DHP and loss of progesterone receptors

leads to increase in myometrial activity (less neg membrane potential, inc OT receptors and gap junctions, inc Ca availability)

43
Q

when is the fetal HPA axis stimulated in horses

A

1-3 days before parturition
- induced fetal lung maturation

44
Q

when does normal parturition occur in horses and how long does it take

A

night time
rapid - 10-30 minutes

45
Q

what can be used to induce parturition and when it is indicated

A

oxytocin and PGF2a (sometimes glucocorticoids but difficult)

should only be done if high risk of dystocia
- need to ensure mare ready to lactate and sacral ligaments are relaxed

46
Q

EQUINE THING 1: are horses seasonal or nonseasonal

A

seasonally polyestrous long day breeders (spring/summer)

47
Q

EQUINE THING 2: are mares ready to breed during their first cycle after entering the breeding season

A

NO - have a transitional period during which the first cycle does not result in ovulation

irregular inter estrus period until first ovulation occurs

48
Q

EQUINE THING 3: what are the stages of equine cycles

A

estrus, diestrus, and seasonal anestrus

49
Q

EQUINE THING 4: is estrus long or short in horses? when does ovulation occur? how big are follicles at ovulation?

A

long estrus (6-7 days)
ovulation occurs BEFORE the end of estrus
follicles are VERY LARGE

50
Q

EQUINE THING 5: what aspects of ovulation are unique to horses

A
  • ovulation rate is limited by the ovulation fossa (can not super ovulate)
  • follicles distort the ovary but CL does NOT
  • ovulation can occur in diestrus
  • twins are rare despite double ovulations
51
Q

EQUINE THING 6: is luteolysis systemic or local

A

systemic - PGF2a from either uterine horn can induce luteolysis in both ovaries

52
Q

EQUINE THING 7: how do embryos migrate into the uterus

A

embryos stimulate their own migration via release of PGE2 to relax oviduct papilla

53
Q

EQUINE THING 8: how do embryos remain spherical

A

embryonic capsule (until day 21/22)

54
Q

EQUINE THING 9: do equine embryos implant and elongate in the uterine horn

A

NO - undergo transplacental migration via secretion of PGE2 until day 11-16 when they become fixed at the base of a uterine horn

55
Q

EQUINE THING 10: can the equine placenta support twins

A

NO - limited surface area/capacity of CA placenta to support twins despite double ovulations

56
Q

EQUINE THING 11: what structure supports pregnancy before the formation of the CA placenta

A

choriovitelline placenta (yolk sac)

regresses once chorioallantoic placenta forms at day 35-40

57
Q

EQUINE THING 12: what structure prevents premature CL regression to maintain progesterone secretion

A

endometrial cups - form at day 35

secrete eCG and stimulate formation of a 2nd CL

58
Q

EQUINE THING 13: when does the CA placenta completely take over progesterone production

A

luteo-placental shift occurs around day 110

59
Q

EQUINE THING 14: what form of progesterone is secreted by the placenta

A

DHP (5a reduced progesterone)

60
Q

EQUINE THING 15: what is unique about equine fetal gonads

A

they are extremely large and secrete DHEA that gets converted to estrone sulphate

(fetoplacental unit)

61
Q

EQUINE THING 16: aside from DHEA, what else does the fetoplacental unit secrete

A

unique conjugated equine estrogens (equilin and equilenin)

62
Q

EQUINE THING 17: what does normal parturition in horses look like

A

occurs at night
rapid
can be induced by OT and PGF2a
return to estrus in 10 days

VET 410: Reproduction (24 decks)

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