13 Canine Anatomy and Estrous Cycle

DOGS: have shorter uterine horns but *long* vagina

COWS/HORSES: have *long* uterine horns but short vagina

How are dogs different from horses and cows in terms of vaginal and uterine horn lengths?

Clitoris

What part of the repro tract is poorly developed in bitches?

Anus

What is 1?

Cutaneous bridge (LONG)

What is 2?

Vulva

What is 3?

Dorsal commissure (this is where you orient your swab towards)

What is 4?

Ventral commissure (clitoris sits just inside here)

What is 5?

Right labia

What is 6?

Left labia

What is 7?

Under developed clitoris

What is the red dot showing?

External uterine bifurcation

What is 1?

Uterine body (TINY)

What is 2?

Uterine horns

What is 3 and 9?

Ovaries

What is 4?

Cranial vagina (LONG)

What is 5?

Vestibule

What is 6?

Vulva

What is 7?

Broad ligament

What is 8?

Adipose tissue

What is 10?

Cranial vagina (opened)

What is 1?

Cervix

What is 2?

Uterine body

What is 3?

Broad ligament

What is 4?

Dorsal median vaginal fold, good to orient yourself when using a scope

What is this? What is it good to use for?

Dorsal median vaginal fold

What is the green dot?

Vaginal fornix (be careful not to get stuck here when breeding)

What is the red dot?

Cervical canal cut open

What is the arrow pointing to?

They have LOTS OF FAT. Arrow pointing to fallopian tube (infundibulum opening to uterine tube)

What is this showing you about bitches?

Internal uterine bifurcation

What is 1?

Urethral tubercle

What is 2?

Clitoral fossa

What is 3?

Labia

What is 4?

When capability of reproduction is attained

How do you describe puberty?

Based on weight

What is puberty related to?

Small: 6-12 mo

Giant: 2 years

What is the typical difference in large and small dog breeds reaching puberty?

2nd, 3rd, or even 4th estrus, around 3 years of life

How long might it take some bitches to reach maximum reproductive capabilities at puberty?

Exhibit signs of bleeding then stop, then start up again maybe 1 month later and finish their heat. Estrus may not occur immediately afterward

Bitches are more likely to exhibit split or false heats during puberty. What does this mean?

Silent heat

This occurs in bitches going thru puberty, where ovulation occurs in the absence of proestrus-estrus behavior or signs

Monestrus. Typically 1-2 estrous cycles per year (normally 3 cycles in 2 years). Non seasonal, peak coming into heat in late winter and early spring but litters are born each month in dogs in general

What is the estrous cycle like in bitches? Describe how many times and when they cycle

Proestrus

This phase of the estrous cycle is the initiation of overt activity, like they start bleeding

Estrus

This phase of the estrous cycle is the time for breeding, when estrogen increases, there are large follicles, they are ready to mate, and some progesterone is present

Diestrus

This phase of the estrous cycle is when pregnancy or pseudopregnancy occurs

note: remember dogs don't have maternal recognition of pregnancy, so this phase of the cycle is the same length of pregnancy

Anestrus

This phase of the estrus cycle occurs when there is a period of quiescence, repair of the repro tract, and noncyclicity

Proestrus: 9 days

Estrus: 9 days

Diestrus: 60 days

Anestrus: 90 days

note: remember these times can vary SEVERELY so it is important to remain flexible. Like pro and estrus can range 2-21 days, anestrus range from 90-150 days

How long does each phase of the estrous cycle typically last in bitches?

Ranges from 90-150 days (3-5 months)

How long does anestrus last?

Estrous cycle lasts for 5-7 months before another begins (168-228 days)

ABOUT how much time is between one cycle to the next in dogs?

Anestrus steady, then peak again at beginning of estrus

When is FSH highest in the estrous cycle in bitches?

Proestrus (though there is a low peak in anestrus, right before proestrus)

note: remember estrogen is decreasing and progesterone is increasing in estrus in bitches because they need BOTH in estrus unlike other animals

When is the largest estrogen peak in the estrous cycle in bitches?

Diestrus

When is progesterone the highest in the estrous cycle in bitches?

Spiking in anestrus, some spikes at the end of diestrus, MAJOR spike right between proestrus and estrus

When is LH spiking in the bitch's estrous cycle?

Interestrus period

note: it says "ESTRUS" not "ESTROUS" so this is literally the time period from one estrus to the next, NOT the time BETWEEN ESTROUS cycles.

This is the time from the end of one estrus to the beginning of the next estrus. How long does it last?

7 months but ranges from 4 months (rottweilers) to 12 months (basenjis)

note: i know this is about as long as the actual estrous cycle itself, however, remember there is a huge variability between dogs, and actual estrus only lasts 9 days so of course the interval is going to be long

On average, how long is the interestrus period in dogs

SHORTER

Larger dogs tend to have *longer or shorter* interestrus periods

LONGER

Older dogs tend to have *longer or shorter* interestrus periods

MINIMUM: 4 months

MAX: 12 months

How long is the absolute MINIMUM estrous cycle length? MAXIMUM?

Fertility decreases (because repair period is necessary after prolonged luteal phase aka diestrus and pregnancy)

What is happening to fertility if anestrus does not occur for at LEAST 90 days?

MINIMUM = shorter interestrus periods

Rottweilers and German shepherds are known for having *minimum or maximum* length estrous cycles

MAXIMUM = around 12 months

African basenjis and sight hounds are known for having *minimum or maximum* length estrous cycles

Vaginal cytology

How do we determine where dogs are in their estrous cycle?

Low estrogen = thinner (2-4 layers)

High estrogen = thicker (20-40 layers)

How does the stratified squamous epithelium of the cranial vagina respond to estrogen?

To protect the vagina against trauma and entrance of bacteria during copulation

Estrogen causes the vagina to grow thicker cell layers. Why?

CAN: if bitch is progressing and still in her fertile period

CAN'T: time of receptivity, LH, or ovulation

What can cornification of vaginal cells in a cytology in bitches tell you? What can it NOT tell you?

Coordinate vaginal cytology with hormone concentration (progesterone) and speculum exam

How can you figure out the estrous cycle and where bitches are in it?

Introduce DRY sterile cotton swab into DORSAL VESTIBULE (straight up) to avoid clitoral fossa and urethra, then go parallel to the ground once you hit to dorsal wall

note: remember vaginas are VERY LONG so the swab will be basically all the way in even with 6 inch ones and that is correct

How do you take a vaginal cytology?

Red: proestrus

What does it mean if the vaginal swab is red versus a brown/clear color?

ROLL

You should *roll or flick* vaginal swab onto microscope slide for cytology

Oil immersion

What setting are you going to view the vaginal cytology on? What view?

Early Proestrus, diestrus, anestrus

Parabasal cells are visible on cytology in what stage of estrous?

Inc. estrogen concentration

What causes larger, more intermediate cornified cells, mostly without nuclei?

*TURGID* swelling of vulva, hemorrhagic vulvar discharge

Name the physical changes that occur to a dog in proestrus

Starting to move away from parabasal cells --> by mid to late proestrus superficial and large intermediate cells (CORNIFIED CELLS) are increasing and parabasal and small intermediates are decreasing.

Also see RBC, WBC (decrease by late proestrus) and *DEBRIS* in back

Name the vaginal cytology changes that occur in a dog in proestrus

Attracts male but not accepting. In early proestrus, aggressively declines, in late proestrus, passive response like sitting down

Describe the behavior changes that occur in a dog in proestrus

Estrogen --> negative feedback to decrease LH and FSH. Progestrone is also low

Which hormone dominants in proestrus? What does this have negative feedback to?

Proestrus = swollen labia and hemorrhagic discharge

What phase of estrous is this dog in?

Proestrus

What phase of estrous is this dog in?

Diestrus = significantly smaller, not turgid

What phase of estrous is this dog in?

Proestrus = still nuclei but becoming angular. looks "dirty"

What phase of estrous is this dog in?

Proestrus

What phase of estrous is this dog in?

Proestrus

What phase of estrous is this dog in?

Proestrus

What phase of estrous is this dog in?

Estrus = softer vulvar swelling, less blood in discharge

What phase of estrous is this dog in?

100% cornification (or very close) and 50% anuclear. NO WBC, FEW RBC, LITTLE TO NO DEBRIS

Name what a vaginal cytology would look like in bitches in estrus

Late max shrinkage (crenulation) and angled mucosa

Describe what you would see in a vaginal speculum in estrus

Stands to be mounted, tail deviates side to side and elevates, muscles around vulva contract and raise vulva, stiff back legs, rolling of skin on back

Talk about the behavior changes that come with bitches in estrus

1. winking (upward tipping of vulva for alignment)

2. curvature of rear legs (lean to the side male is approaching from)

3. flagging (deviation of tail opposite to where male is touching)

What are the *3 main sexual responses* bitches have during estrus

FLAGGING = ESTRUS

What phase of estrous is this dog in?

Estrogen begins to fall and progesterone begins to rise. *first rise of progesterone correlated with LH peak*. BOTH estrogen and progesterone necessary for standing behavior in bitch

Describe what the hormones are like during estrus in bitches

Lutenization of follicles during estrus = *estrual lutenization*

What causes the preovulatory rise of progesterone in bitches?

Diestrus

What phase of estrous is this dog in?

Estrual lutenization

This process causes preovulatory rise of progesterone in bitches, where there is lutenization of follicles during estrus

Diestrus

What phase of estrous is this dog in?

Anestrus

What phase of estrous is this dog in?

LEFT: proestrus = rounded mucosa

RIGHT: estrus = angled or crenulated mucosa

What is the difference in the speculum here?

Estrus

What phase of estrous is this dog in?

Estrus

What phase of estrous is this dog in?

Estrus

What phase of estrous is this dog in?

Estrus

What phase of estrous is this dog in?

Changes in behavior = no acceptance of male

What begins diestrus of bitches?

Progesterone

What hormone dominates during diestrus

Luteal

Is diestrus part of the *luteal or follicular* phase