1. Estrous Cycle of the Bitch Flashcards
do bitches ovulate mature eggs? how long do eggs take to become mature? does the oocyte need to be mature to be fertilized?
Do not ovulate mature eggs
◦ Takes 48 hours on average to become mature
◦ Canine oocytes have longer lifespan > extends the breeding period but fertilization can only occur once the oocytes are mature.
what hormone level rises before ovulation?
Progesterone levels begin to rise prior to ovulation
◦ Use progesterone to determine when ovulation occurs
◦ Hormones are the same pregnant or not
The stages of the canine estrous cycle
proestrus, estrus, diestrus, anestrus
are canines poly or mono estrus?
monoestrus, non seasonal
proestrus+ estrus =
heat
when is bitch puberty?
When the first proestrus occurs
Occurs earlier in small breeds vs. large breeds
◦ Average 8-14 months (range 6 – 26 months)
should we breed on first heat?
no
how is the first heat likely to differ from subsequent heats?
Likely to be “irregular” compared to other cycles ◦ Split or silent heats common
what is a split heat?
Split heat = heat starts then stops without ovulation. Starts again later.
what is a silent heat?
Silent heat = very little vaginal discharge.
4 strategies we can use to determine the stage of estrus
Vaginoscopy
Vaginal cytology
Progesterone levels
Behavior/receptivity
average length of proestrus?
Average length = 9 days (0-27 day range)
what day of heat do we see the first drop of blood?
day 1
what hormone level rises during proestrus? how does this effect the vagina and vulva?
Estrogen levels are rising
◦ Edema of vaginal epithelium; edema of the vulva
external cues of proestrus?
◦ Swollen vulva
◦ Serosanguineous vaginal discharge
◦ May start “flagging”
behavioural changes during proestrus?
Males are interested in the bitch
*Bitches are typically not receptive yet
*Bitches may mount other bitches
*Bitches in heat may become aggressive towards other bitches
vaginal epithelium changes during proestrus?
Vaginal epithelium > goes from 5-10 cell layers to 10-20 cell layers
Cytology of vaginal swab
*Parabasal cells, intermediate cells
average length of estrus
Average length = 9 days (4-24 day range)
hormone changes during estrus
Stage at which LH surge occurs, ovulation occurs and fertile period occurs = when breeding occurs “standing heat”
Estrogen levels elevated initially; peak; starts decreasing at LH
Progesterone levels start to rise at LH, continue to elevate at ovulation & remain elevated
how can we estimate the LH surge?
We can use progesterone to estimate the LH surge
◦ Coincides with the initial progesterone rise
Or can use in house LH test (Witness® LH)
◦ Usually reserved for important breedings; frozen semen breedings
◦ Can get costly, time consuming
◦ More accurate
how does LH surge timeline relate to ovulation?
LH surge occurs 48 hours before ovulation
how do we measure progesterone?
Ran on SERUM (ideally separated 20-30 mins after blood draw)
Place in red top tube
◦ No serum separator tubes
vulva and vagina changes during estrus
Vulva becomes less turgid as estrogen decreases, serosanguineous discharge can diminish, can become lighter
Edema of vaginal epithelium decreases = crenulation
what behaviours will the female engage in during her fertile period?
Female should be receptive to male during fertile period ◦ Flagging
◦ Seeks out the male
vaginal epithelium characteristics during estrus?
Vaginal epithelium > 20-30 cell layers at estrogen level peak
Cytology of vaginal swab
◦ Cornified epithelial cells
length of diestrus?
Length = average 2 months (range 56-58 days if pregnant; if not pregnant 56-90 days)
◦ If pregnantà62-64 days from ovulation (canine gestation = 63 days +/- 1 day)
is bitch receptive to breeding during diestrus?
Bitch is no longer in “heat”
◦ No longer receptive to breeding
when does diestrus occur relative to ovulation?
Occurs 6 days after ovulation (or 8 days from the LH surge)
vulva and vagina changes during diestrus?
Vulva diminishes in size, vaginal discharge subsides, vaginal epithelium flattens
hormone profile during diestrus?
Period of time when progesterone is high; estrogen is low
vaginal epithelium characteristics during diestrus?
Vaginal epithelium peels off > goes back to 5-10 cell layers > 2-4 cell layers
Cytology of vaginal swab
◦ Parabasal cells
◦ Intermediate cells
◦ Neutrophils
length of anestrus?
Length = average 4 months (range 4-12 months)
what hormone drops during anestrus?
Progesterone drops
what is anestrus? what is it important for? vaginal and vulvar character?
Period of reproductive quiescence Important stage for uterine involution
◦ Uterine involution is a necessary process Bitches are not receptive to breeding
Vulva small, no vaginal discharge
Reproductive Consultation - why is it important?
◦ Our responsibility to educate clients on responsible breeding
◦> Time commitment
◦> $$$
◦ Should only be breeding mature, healthy, good dogs
◦> Clearances
◦>Representative of the breed
Bitch breeding management considerations
History
◦ Medical
◦ Reproductive (Brucella canis status)
Physical exam
Reproductive exam
◦ Digital palpation
◦ Vaginal swab for cytology ◦ Vaginoscopy
Serum progesterone levels
◦ Usually blood taken every 2 days
Breeding methods
Natural
Vaginal artificial insemination (AI)
◦ Plastic pipette ($)
◦ MAVIC catheter ($$)
Transcervical insemination (TCAI)
◦ $$$
◦ Semen is directly deposited in uterus ◦ Can usually do without any sedation
Surgical insemination (SAI)
◦ $$$$
◦ Semen is directly deposited in the uterus
◦ More invasive than TCAI – surgery under general
anesthesia
Pregnancy rates equivalent for TCAI as they are for SAI
Types of semen
Fresh
◦ Can breed with standard vaginal AI, MAVIC catheter or TCAI
Fresh chilled
◦ Semen collected, evaluated (hopefully), processed elsewhere & shipped
◦ Is stored cool, not frozen
◦ Increased timing is required > need to give stud dog owner 24-48hrs notice
◦ Should be shipped 24hr priority > allows for semen from the US or in other parts of Canada to be used
◦ Standard vaginal AI, MAVIC or TCAI
Frozen
◦ TCAI or SAI only
◦ More in depth timing is required (confirm ovulation date with LH witness test)
◦ Progesterone timing every 2 days
◦ Stored in liquid nitrogen
◦ Can be shipped internationally (Europe, Australia, etc.).
Take home points: estrogen levels during heat and effect, pogesterone surge timiing, LH surge timing, fertile period. More processed semen means what?
Estrogen is elevated in heat
◦ Edema of vulva
◦ Edematous vaginal epithelium
◦ Cornification on cytology
Progesterone rises prior to ovulation
◦ Use progesterone to determine ovulation date
◦ Rise typically coincides with LH surge
LH surge occurs 48 hours prior to ovulation Dogs ovulate immature eggs
◦ Fertile period = 2-4 days post ovulation
The more ”processed” the semen is = more precise timing required
