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VET 410: Reproduction > Bovine Cyclicity > Flashcards

Bovine Cyclicity Flashcards

1
Q

are cows seasonal or nonseasonal

A

nonseasonally polyestrous

cycle every 21 days

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2
Q

is anestrus normal in a cow

A

NO unless:
- pregnant
- prepubertal
- suckling

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3
Q

is luteolysis in cows spontaneous or gradual/senescent

A

spontaneous
can shorten luteal phase if pregnancy is not established via uterine prostaglandins

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4
Q

how long is the follicular phase in cows

A

SHORT (2-3 days)

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5
Q

what are signs of estrus in cows

A

stands to be mounted
clear secretions from vulva
increased uterine tone

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6
Q

when does ovulation occur

A

12 hours AFTER estrus ends

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7
Q

when does luteinization occur

A

AFTER ovulation

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8
Q

what are the stages of the bovine cycle

A
  1. proestrus
  2. estrus
  3. metestrus
  4. diestrus

NO anestrus unless pregnant/prepubertal/suckling

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9
Q

proestrus

A

mounting/chasing other females

short - 12-24 hours

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10
Q

estrus

A

stands to be mounted, clear secretions from vulva

short - 12-24 hours

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11
Q

metestrus

A

period of CL formation that occurs after ovulation

bloody discharge from vulva

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12
Q

diestrus

A

luteal phase

long - 19-20 days

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13
Q

is follicular development from primordial to tertiary follicles FSH dependent or independent

A

FSH independent - follicles can grow prior to puberty but oocyte will NOT ovulate

follicles will undergo atresia

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14
Q

is follicular development from tertiary to Graafian follicles FSH dependent or independent

A

FSH dependent - can only occur after puberty

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15
Q

how many oocytes ovulate per cycle

A

1-2

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16
Q

do cows ovulate a primary or secondary oocyte

A

secondary oocyte - can get fertilized immediately after ovulation to induce the resumption of meiosis

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17
Q

do follicules get recruited throughout the cycle or only during follicular phase

A

follicles get recruited in waves throughout the cycle

if recruited during luteal phase: undergoes atresia due to high progesterone

if recruited during follicular phase: 1 will ovulate (progesterone is low)

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18
Q

progesterone and estradiol levels during estrus/ovulation

A

HIGH estrus
LOW progesterone

unlike dogs - do NOT need progesterone to trigger estrus

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19
Q

is the LH surge long or short

A

SHORT and sharp - ovulation is rapid and occurs 12 hours after estrus

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20
Q

is there an FSH surge along with LH surge in response to GnRH

A

NO because growing follicles also release inhibin B - negative feedback on FSH prevents FSH surge

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21
Q

post ovulatory luteinization

A

LH surge stimulates granulosa cells to express LH receptors –> starts secreting progesterone

occurs AFTER ovulation due to rapid estrus and ovulation

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22
Q

what hormone is responsible for inducing spontaneous luteolysis

A

prostaglandin F2a (PGF2a)

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23
Q

spontaneous luteolysis in cows

A

at the end of the luteal phase, if no fertilization:
- ipsilateral uterine horn releases PGF2a
- PGF2a travels in uterine vein then diffuses into ovarian artery
- PGF2a travels back to the ipsilateral ovary
- induces regression of the CL

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24
Q

can local induction of luteolysis occur in other species besides cows

A

NO because the vascular architecture allows the UV and OA to be closely related for PGF2a to diffuse across easily

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25
Q

can PGF2a released from one uterine horn affect the contralateral ovary in cows

A

NO because PGF2a that enters systemic circulation gets metabolized in the lung (pulmonary epithelium)

insufficient amounts make it back to the contralateral ovary - not enough to induce luteolysis

26
Q

what is the +/+ feedback loop of OT and PGF2a

A

corpus luteum will produce OT to aid in inducing luteolysis

  1. CL produces OT
  2. OT binds receptors on endometrium
  3. stimulates PGF2a release from uterus
  4. PGF2a travels from UV to OA back to the ipsilateral ovary
  5. induces luteolysis of the CL
27
Q

superovulation

A

exogenous administration of FSH during the luteal phase can “rescue” follicles that would otherwise become atretic

FSH will NOT stimulate follicle growth, only rescue existing follicles from atresia

28
Q

AM/PM rule of cows

A

when cows are in heat in the morning, inseminate them in the evening (12 hours later) and vice versa because ovulation occurs 12 hours post-heat

want sperm present at time of ovulation because secondary oocytes have a short lifespan once ovulated and sperm has short lifespan in female repro tract

29
Q

cycle synchronization/shortening

A

exogenous PGF2a can be administered 5-6 days after ovulation to shorten the cycle and synchronize the herd

must be administered once CL is fully formed and responsive to PGF2a (5-6 days)

30
Q

what hormone prepares the endometrium for pregnancy during early luteal phase

A

progesterone

stimulates endometrial secretions in order to synchronize embryonic and endometrial development (ensures adequate environment for embryo to grow)

31
Q

days/events of embryonic development

A

day 1 to 4/5: embryo develops in oviduct
day 5: enters uterus
day 12: elongates to fill uterine horn
day 17: MRP

32
Q

maternal recognition of pregnancy

A

physiologic prevention of luteolysis resulting from embryonic secretion of interferon tau

33
Q

why does luteolysis need to be prevented in order to maintain pregnancy

A

progesterone is necessary to allow for coordinated/synchronized embryonic and endometrial development

composition of uterine secretions changes throughout pregnancy - need progesterone to control secretions

34
Q

interferon tau

A

secreted by the embryo prior to luteolysis

downregulates OT receptors to prevent the +/+ feedback loop of OT and PGF2a
- decreased stimulation of PGF2a allows CL to persist
- persistent CL continues secreting progesterone

35
Q

is MRP local or systemic in cows

A

local due to vascular architecture

embryo will prevent PGF2a secretion from the IPSILATERAL horn only - will not be affected by PGF2a from the contralateral horn

36
Q

does MRP occur in carnivores

A

NO because luteolysis is not spontaneous in carnivores

37
Q

when is the fetus able to start developing

A

once the placenta is formed (day 40)

required to allow for the exchange of nutrients and waste

38
Q

at what part of gestation does the majority of fetal development occur

A

last 1/3 of gestation

39
Q

is the placenta able to produce progesterone in cows

A

yes after day 150

CL is NOT needed from day 150-240 (is needed again from 240-280; unknown why)

40
Q

what are early signs of pregnancy on rectal palpation

A
  1. amniotic vesicle in ipsilateral horn (day 35-60)
  2. membrane slip (intercaruncular spaces; day 42+)
41
Q

what are later signs of pregnancy on rectal palpation

A
  1. fetus (day 65+)
  2. caruncles (day 90+)
  3. fremitus (day 150)
42
Q

fremitus

A

turbulent blood flow in the uterine artery causing a “fluid thrill”

43
Q

what 3 ways are used to diagnose pregnancy in cows

A
  1. rectal palpation - day 35 earliest
  2. ultrasound - day 28 earliest
  3. pregnancy specific protein B - day 24 earliest
44
Q

progesterone withdrawal

A

the drop in progesterone that occur within a few days of parturition to initiate fetal expulsion

45
Q

fetal HPA axis

A

increases in fetal cortisol secretion prior to parturition induces an increase in placental estradiol and endometrial PGF2a secretion to initiate parturition

46
Q

pre partum surge of PGF2a

A

fetal cortisol –> surge of PGF2a –> rapid luteolysis/CL regression –> decreased progesterone

47
Q

effects of high estradiol and low progesterone at parturition

A
  • induces cervical relaxation
  • increases myometrial membrane potential
  • increases oxytocin receptors
  • increases gap junctions
48
Q

what hormones can be administered exogenously to induce abortion/early parturition

A

PGF2a or dexamethasone (depends on timeline)

PGF2a alone: works during months 1-5 and 7-9
dex alone: works during months 7-9
PGF2a + dex: works during months 5-7

49
Q

Ferguson reflex

A

neuroendocrine reflex triggered by cervical stretch receptors resulting in OT secretion

oxytocin stimulates:
- myometrial contractions
- +/+ feedback with PGF2a

50
Q

tocolytics

A

administration of B adrenergic agonists to delay parturition for a SHORT period of time

increases cAMP in smooth muscle –> decreases Ca –> decreases uterine contraction

51
Q

BOVINE THING 1: are cows seasonal and do they experience anestrus

A

non-seasonal - cycle year round
anestrus is abnormal unless pregnant, prepubertal, or suckling

52
Q

BOVINE THING 2: is estrus long or short

A

SHORT (<24 hrs)

53
Q

BOVINE THING 3: when does ovulation occur

A

ovulation occurs 12 hours after estrus ENDS

AM/PM rule

54
Q

BOVINE THING 4: how long do sperm remain viable in the repro tract

A

SHORT - especially if not fresh (AI)

55
Q

BOVINE THING 5: what allows super ovulation to occur in cows

A

follicles emerge in waves throughout enter cycle (including luteal phase)

super ovulation uses FSH to “rescue” the follicles released during luteal phase

56
Q

BOVINE THING 6: is luteolysis local or systemic

A

local - uterine PGF2a only reaches the ipsilateral ovary due to vascular architecture of the uterine vein and ovarian artery

57
Q

BOVINE THING 7: what hormone stimulates uterine PGF2a to initiate luteolysis

A

oxytocin secreted from the corpus luteum (+/+ feedback)

58
Q

BOVINE THING 8: is MRP local or systemic

A

local - interferon tau secreted from the embryo suppresses PGF2a secretion from the ipsilateral uterine horn

59
Q

BOVINE THING 9: how is pregnancy maintained after day 150

A

placental progesterone

can support until day 240 (still need CL past then)

60
Q

BOVINE THING 10: what initiates parturition

A

luteolysis - induced by stimulation of fetal HPA axis –> high cortisol –> high PGF2a from endometrium

VET 410: Reproduction (24 decks)

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