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VET 410: Reproduction > Canine Cyclicity > Flashcards

Canine Cyclicity Flashcards

1
Q

cyclicity

A

predictably recurring egg release every few weeks (livestock) or months (dogs)

achieved once cycles are reliably timed

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2
Q

are dogs seasonal or nonseasonal breeders

A

non seasonal

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3
Q

how long is the interval between canine estrous cycles

A

6 to 15 months (cycles 1-2x per year)

varies by the length of anestrus between cycles (age and breed dependent)

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4
Q

what stages of the estrous cycle do dogs have

A
  1. proestrus
  2. estrus
  3. metestrus
  4. diestrus
  5. anestrus
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5
Q

proestrus

A

female becomes sexually attractive but will not stand to mount

estradiol dominant; ~9 days

bloody discharge from vulva

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6
Q

estrus

A

standing for mating

estradiol and progesterone dependent (estradiol peaks, progesterone starts to increase)

~9 days; ends with ovulation

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7
Q

metestrus

A

formation of the corpus luteum

high progesterone, low estradiol

short; ~1-2 days

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8
Q

diestrus

A

fully functional corpus luteum

progesterone dominant

~60 days (progesterone peaks around day 35)

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9
Q

anestrus

A

period of no cyclicity (complete ovarian inactivity)

length of anestrus determines interestrus interval

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10
Q

effect of estradiol in proestrus and estrus

A
  • secreted by follicles as they grow (inc size = inc amount secreted)
  • causes females to be attractive to males
  • females start to show interest BUT NEED PROGESTERONE for receptivity
  • increases vaginal secretions and cervical relaxation
  • increases vaginal cornification (thickening of mucosa)
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11
Q

what is a vaginal cytology

A

sampling of the cell types present on vaginal mucosa to determine stage of cyclicity

mostly used in dogs

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12
Q

parabasal epithelial cells

A

vaginal epithelial cells

indicates ANESTRUS

gross appearance: red/pink mucosa

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13
Q

cornfield/keratinized epithelial cells

A

thickened and keratinized epithelial cells in response to estradiol or chronic irritation

indicates ESTRUS

gross appearance: white/folded (crenelation) mucosa

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14
Q

what does the present of neutrophils on vaginal cytology represent

A

indicates ANESTRUS

disappears during proestrus and estrus

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15
Q

metestrual cell

A

neutrophil within a parabasal cell

indicates the reappearance of neutrophils during DIESTRUS

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16
Q

effect of progesterone in estrus, diestrus, and pregnancy

A

secreted by luteinized follicles (pre-ovulation) and corpus luteum (post-ovulation)

in the presence of estradiol: signals receptivity –> estrus

in the absence of estradiol: suppresses receptivity –> diestrus
- peaks during diestrus (luteal phase)
- suppresses ovulation
- decreases vaginal secretions and induces cervical closure
- stimulates oviduct and endometrial secretions (supports pregnancy)
- inhibits neutrophil activation

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17
Q

when does lutenization of granulosa/theca cells occur in dogs

A

pre-ovulation

increases progesterone to induce estrus and ovulation

(both estradiol and progesterone required for estrus)

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18
Q

are dogs spontaneous or induced ovulators

A

spontaneous (induced by hormones)

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19
Q

what are the feedback mechanisms involved in canine ovulation

A
  1. pulsatile secretion of GnRH –> LH/FSH –> follicle development in ovary
    - follicles secrete increasing amounts of estradiol as they grow
    - low [estradiol] = NEGATIVE FEEDBACK = prevents ovulation
  2. spontaneous surge secretion of GnRH –> LH –> ovulation
    - once follicles get large enough, the amount of estradiol secreted reaches a threshold to stimulate POSITIVE FEEDBACK on surge center neurons –> GnRH surge –> LH surge (not FSH b/c of inhibin B) –> ovulation
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20
Q

does progesterone have positive or negative feedback on GnRH secretion

A

negative - once diestrus is reached, corpus luteum forms to secrete high amounts of progesterone –> prevents ovulation during diestrus

21
Q

what do granulosa cells secrete and what stimulates their secretion

A

estrogens and inhibins

stimulated by FSH

22
Q

what do theca interna cells secrete and what stimulates their secretion

A

androgens (testosterone)

stimulated by LH

testosterone crosses the basement membrane into the follicle to get converted to estradiol

23
Q

how does the LH surge induce ovulation

A

LH binding to theca cells induces erosion by proteases of the outer follicular wall at the site of future ovulation

weakens the wall to allow oocyte to rupture through

24
Q

how does the LH surge induce luteinization

A

LH surge stimulates granulosa cells to transform from FSH responsive/estradiol secreting cells into LH responsive/progesterone secreting cells
(loss of FSH receptor, gain of LH receptor)

occurs BEFORE ovulation in dogs to increase progesterone to induce estrus/ovulation

25
Q

steps of oocyte development

A
  1. oogenesis (pre birth)
  2. oocyte maturation (pre pubertal)
  3. puberty
  4. fertilization
26
Q

oogenesis

A

mitosis of primordial germ cells into diploid oogonia

occurs during fetal development

27
Q

oocyte maturation

A
  1. meiosis of oogonia starts
  2. arrested almost immediately during prophase I
  3. some follicles get recruited to grow, but since oocyte is arrested, follicles will undergo atresia
28
Q

puberty

A
  1. first LH surge re-initiates meiosis in the oocytes to form a primary oocyte
    - in dogs: ovulation occurs before loss of first polar body
  2. oocytes lose first polar body
    - in dogs: occurs 2-3 days after ovulation
  3. second meiotic arrest during prophase II
29
Q

fertilization

A
  1. fertilization of the egg by the sperm induces resumption of meiosis
  2. meiosis is completed
  3. oocytes lose second polar body
  4. zygote forms
30
Q

what is the difference in progesterone concentrations in a non-pregnant dog in diestrus vs a pregnant dog

A

relatively similar progesterone concentrations during luteal phase and majority of gestation (both ~2 months long)

pregnant: progesterone drops (“withdrawal”) a couple days before whelping

diestrus: progesterone levels senesce until CL is completely regresses

31
Q

is it possible to shorten the luteal phase in dogs if pregnancy is not established

A

NO because luteolysis is not spontaneous

32
Q

function of prolactin in dogs

A

required to support pregnancy during the second half (day 35+) by maintaining the corpus luteum

CL requires prolactin to slow the rate of regression and continue secreting progesterone

33
Q

prolactin, progesterone, and prostaglandin levels during whelping

A

high prolactin - stimulates nesting behavior, mammary development, and lactation

low progesterone - “progesterone withdrawal”; initiates lactation

high prostaglandin - stimulates myometrial contraction and placental separation

34
Q

how is cardiovascular function altered during pregnancy

A

increased blood flow to uterus by increasing CO, SV, and HR

decreased vascular resistance to prevent hypertension

35
Q

how do canine embryos adjust if there is an unequal amount in each uterine horn

A

embryos will migrate to equal out the amount in each uterine horn

allows blood flow to be equally distributed

36
Q

what disease are pregnant dogs predisposed to

A

diabetes mellitus

pregnancy –> high progesterone –> stimulates mammary tissue development –> increases GH secretion

GH is an insulin antagonist (insulin resistance)

37
Q

canine pseudopregnancy

A

non-pregnant female that starts to lactate/nest/exhibit other prepartum behaviors due to high levels of prolactin

occurs in females spayed around day 35 of their cycle causing premature progesterone withdrawal
- high PRL + low PRG stimulates prepartum behaviors

can treat with dopamine agonists (dopamine inhibits prolactin)

38
Q

canine ovarian remnant syndrome (ORS)

A

small piece of ovarian tissue remaining after OVH

leads to elevated AMH - diagnostic

remanant tissue will be hyperstimulated due to loss of ovarian tissue –> loss of negative feedback on GnRH –> increase GnRH, LH, FSH –> overstimulates remnant tissue to secrete estradiol

high risk of GCTs
- if hormonally functional: can get revascularization of remnant tissue

39
Q

DOG THING 1: is the interval between estruses constant or variable in dogs

A

variable (6-15 months)

40
Q

DOG THING 2: when do blood tinged secretions occur in dogs

A

proestrus (sometimes into estrus)

41
Q

DOG THING 3: when does progesterone start increasing in dogs

A

PRE OVULATORY -
in response to LH surge

42
Q

DOG THING 4: do dogs ovulate a primary or secondary oocyte

A

primary - still has first polar body

need to lose first PB (secondary oocyte) before oocyte can be fertilized

fertilization occurs 2-3 days after ovulation

43
Q

DOG THING 5: how long can canine sperm remain viable in the female repro tract

A

days - beneficial due to ovulation of a primary oocyte

44
Q

DOG THING 6: can females shorten their luteal phase to re-enter estrus if she does not become pregnant

A

NO because luteolysis is not spontaneous; CL senesces slowly until completely regresses

45
Q

DOG THING 7: what maintains the corpus luteum after day 35 of gestation

A

prolactin

46
Q

DOG THING 8: what hormone gets secreted by mammary tissue in response to progesterone

A

GH - leads to insulin resistance and diabetes mellitus

47
Q

DOG THING 9: what pigment is released from the placental marginal hematomas and what does it indicate

A

biliverdin - released as placenta detaches

indicates second stage labor

48
Q

DOG THING 10: what causes overt pseudopregnancy

A

elevated prolactin from premature progesterone withdrawal in females spayed before day 35

49
Q

DOG THING 11: what hormone is diagnostic for ORS

A

AMH - should be 0 in spayed females

VET 410: Reproduction (24 decks)

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