Canine Cyclicity Flashcards by Jessica Hodson

cyclicity

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

achieved once cycles are reliably timed

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are dogs seasonal or nonseasonal breeders

non seasonal

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how long is the interval between canine estrous cycles

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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what stages of the estrous cycle do dogs have

proestrus
estrus
metestrus
diestrus
anestrus

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proestrus

female becomes sexually attractive but will not stand to mount

estradiol dominant; ~9 days

bloody discharge from vulva

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estrus

standing for mating

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

~9 days; ends with ovulation

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metestrus

formation of the corpus luteum

high progesterone, low estradiol

short; ~1-2 days

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diestrus

fully functional corpus luteum

progesterone dominant

~60 days (progesterone peaks around day 35)

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anestrus

period of no cyclicity (complete ovarian inactivity)

length of anestrus determines interestrus interval

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effect of estradiol in proestrus and estrus

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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what is a vaginal cytology

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

mostly used in dogs

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parabasal epithelial cells

vaginal epithelial cells

indicates ANESTRUS

gross appearance: red/pink mucosa

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cornfield/keratinized epithelial cells

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

indicates ESTRUS

gross appearance: white/folded (crenelation) mucosa

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what does the present of neutrophils on vaginal cytology represent

indicates ANESTRUS

disappears during proestrus and estrus

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metestrual cell

neutrophil within a parabasal cell

indicates the reappearance of neutrophils during DIESTRUS

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effect of progesterone in estrus, diestrus, and pregnancy

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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when does lutenization of granulosa/theca cells occur in dogs

pre-ovulation

increases progesterone to induce estrus and ovulation

(both estradiol and progesterone required for estrus)

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are dogs spontaneous or induced ovulators

spontaneous (induced by hormones)

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what are the feedback mechanisms involved in canine ovulation

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
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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does progesterone have positive or negative feedback on GnRH secretion

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

what do granulosa cells secrete and what stimulates their secretion

estrogens and inhibins

stimulated by FSH

what do theca interna cells secrete and what stimulates their secretion

androgens (testosterone)

stimulated by LH

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

how does the LH surge induce ovulation

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

how does the LH surge induce luteinization

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

steps of oocyte development

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

oogenesis

mitosis of primordial germ cells into diploid oogonia occurs during fetal development

oocyte maturation

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

puberty

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

fertilization

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

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

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

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

NO because luteolysis is not spontaneous

function of prolactin in dogs

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

prolactin, progesterone, and prostaglandin levels during whelping

high prolactin - stimulates nesting behavior, mammary development, and lactation low progesterone - "progesterone withdrawal"; initiates lactation high prostaglandin - stimulates myometrial contraction and placental separation

how is cardiovascular function altered during pregnancy

increased blood flow to uterus by increasing CO, SV, and HR decreased vascular resistance to prevent hypertension

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

embryos will migrate to equal out the amount in each uterine horn allows blood flow to be equally distributed

what disease are pregnant dogs predisposed to

diabetes mellitus pregnancy --> high progesterone --> stimulates mammary tissue development --> increases GH secretion GH is an insulin antagonist (insulin resistance)

canine pseudopregnancy

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)

canine ovarian remnant syndrome (ORS)

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

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

variable (6-15 months)

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

proestrus (sometimes into estrus)

DOG THING 3: when does progesterone start increasing in dogs

PRE OVULATORY - in response to LH surge

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

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

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

days - beneficial due to ovulation of a primary oocyte

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

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

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

prolactin

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

GH - leads to insulin resistance and diabetes mellitus

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

biliverdin - released as placenta detaches indicates second stage labor

DOG THING 10: what causes overt pseudopregnancy

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

DOG THING 11: what hormone is diagnostic for ORS

AMH - should be 0 in spayed females