Lecture 13: Canine Anatomy & Estrous Cycle

What are these important anatomical structures?

A – ANUS

CB – CUTANEOUS BRIDGE

DC – DORSAL COMMISSURE

LL – LEFT LABIA

RL – RIGHT LABIA

VC – VENTRAL COMMISSURE

What are these important anatomical structures?

Ad – Adipose tissue

BL – Broad Ligament

CV – Cranial Vagina

O – Ovary

EUB – External Uterine Bifurcation

UtB – Uterine Body

UH – Uterine Horn

Ve – Vestibule

Vu - Vulva

What are these important anatomical structures?

EUB – External Uterine Bifurcation

UH – Uterine Horn

IUB – Internal Uterine Bifurcation

UB – Uterine Body

BL – Broad Ligament

UtB – Uterine Body

CX - Cervix

CV – Cranial Vagina

UT – Urethral Tubercle

Ve – Vestibule

L – Labia

CF – Clitoral Fossa

What is this structure in a bitch?

dorsal-median vaginal fold

What are these important anatomical structures?

Dorsal median vaginal fold (green dot), vaginal fornix (red dot), cervical canal cut open (arrow)

What tissue normally surrounds the ovary?

significant amounts of adipose tissue

When are dogs considered in puberty?

• When the capability of reproduction is attained

• Timing related to reaching a certain plateau in growth

• 6 to 12 months in smaller breeds (Corgi ~9 months)

• Nearly 2 years for some giant breeds (Great Dane – up to 18 months)

• Can be quite variable in some breeds (English Setter 7-20 months)

• Maximum reproductive capability may not be reached until 2nd, 3rd or 4th estrus or ~ 3 years of life

True or false: Pubertal bitches may be less likely to demonstrate estrus when ovulation occurs.

true - more likely to have split or false heats (Exhibit signs of proestrus (bleeding), but estrus may not occur immediately afterwards – may be days or weeks) or silent heats (Ovulation occurs in absence of proestrus-estrus behavior or signs)

What is the timing of the canine estrous cycle?

• Monestrus (bitch, wolves, bears)

• Typically 1-2 estrous cycles per year - May have one to four

• Non-seasonal typically: Environment may influence, Peak in late winter and spring (Feb to May), Litters born during each month though

What are the stages of the canine estrous cycle?

• Proestrus - initiation of overt activity

• Estrus - time for breeding

• Diestrus - pregnancy or pseudopregnancy

• Anestrus - period of quiescence and repair

What is the average duration for proestrus and estrus in dogs?

• Average duration for each is 7-9 days (total 14-18 days)

• Range: 2-21 days (bitches don’t read the book)

• Take-home message - must remain flexible when managing individual bitches for breeding

How long is canine anestrus?

usually 90-150+ days

How long till next canine cycle (inter-estrus period)?

5-7 months

True or false: larger dogs tend to have shorter inter-estrus periods and older dogs tend to have longer inter-estrus periods.

true

What is the minimum estrous cycle length?

• Absolute requirement of 4 months

• Fertility is low if at least a 90 day anestrus is not achieved

What is the maximum estrous cycle length?

12 months

How is cycle pattern determined by use of vaginal cytology?

• Response of stratified squamous epithelium of (cranial) vagina to estrogen

  • Normally (low estrogen) thin: 2-4 cell layer thickness in anestrus

  • Estrogen response of the vagina causes growth to 20-40 cell layer thickness by end of proestrus

• Protection of vagina against trauma and prevent entrance of bacteria

What needs to be coordinated with vaginal cytology to figure out cycle?

hormone concentration and speculum examination

What can cornification of vaginal cells tell you?

Period of maximum cornification varies between bitches

• Can’t be used to accurately predict time of receptivity, LH surge, or ovulation

• Can tell you if the bitch is progressing and if she is still in her fertile period

What is the procedure for taking vaginal cytology?

1. Introduce dry sterile cotton-tipped swab into dorsal vestibule or caudal vagina

2. Pre-moisten swab if bitch has dry secretions, but most of the time she has adequate moisture

3. Avoid clitoral fossa and urethra → Go straight up with the swab until reaching the dorsal wall of the vestibule, then re-orient swab to parallel to the ground and go straight in; Remember very long vagina (even in small dogs), so the swab should go in pretty far

How do you evaluated a vaginal cytology?

• Make note of color of swab: More red – she is in proestrus, Stops being red in estrus

• Roll swab gently on clean microscope slide → Make 2-3 lines of cells

• Air dry slide

• Use Diff-Quik to stain

• Scan on 40x and 100x objectives (400x and 1000x)

• Use oil immersion

What are these three cells seen on a vaginal cytology?

What are the physical changes seen during proestrus (coming into heat)?

• Turgid swelling of vulva

• Hemorrhagic vulvar discharge - Diapedesis of RBC’s through uterine vessels – variable in individuals

What are the vaginal cytology changes seen during proestrus (coming into heat)?

• Cornification of squamous epithelial lining of vagina

• By mid to late proestrus, parabasal and small intermediate cells decrease, superficial and large intermediate cells increase, erythrocytes, neutrophils

What are the changes seen on a vaginal speculum exam during proestrus (coming into heat)?

• Early vaginal mucosa edematous

• Late starts shrinking, less edema

What is the behavior associated with proestrus?

• Attracts male, but not accepting: Sex pheromones in vaginal secretions, anal sac secretions or urine

• Early Proestrus: Negative responses - growling, snapping, aggression

• Late Proestrus: Passive responses - sits down when dog attempts mounting - tucks tail

What are the proestrus hormone profiles?

• Estrogen Dominates

• Gonadotropins - LH and FSH - Low

• Progesterone Low (< 1 ng/ml)

What phase of the estrous cycle is this? note the swollen labia and hemorrhagic discharge.

proestrus

What phase of the estrous cycle is this?

late proestrus

What phase of the estrous cycle is this?

diestrus

How does vaginal cytology present during proestrus?

• Cornified epithelial cells increasing: Have a “corn flakes” appearance, Large angular cells with small to no nuclei

• Red blood cells

• White blood cells - PMN’s (polymorphonuclear neutrophils): Variable in number, Decreasing in amount over time

• Debris in the background

What phase of the estrous cycle is this?

proestrus

What phase of the estrous cycle is this?

proestrus

What are the physical, vaginal cytology, and vaginal speculum exam changes during estrus?

• Physical changes: Softening of vulvar swelling, Less blood in discharge

• Vaginal cytology: Cornification continues

• Vaginal speculum: Early more shrinking of mucosa, Late max shrinkage called crenulation, angled mucosa

What are the behavior changes associated with estrus?

• Definition - “Stands to be mounted”

• Tail deviated to side and elevated

• Muscles around vulva contract and raise vulva: Helps alignment of penis

• Stiffening of back legs

• Rolling of skin on back

What are the three sexual responses associated that increase during proestrus and peak in early to mid estrus?

1. Winking

• Upward tipping of vulva to touching skin above vulva

• Aligns vulva to penis

2. Curvature of rear legs

• Same side as to tapping skin to right or left of vulva

• Leaning to the side that the male is approaching from

3. Flagging

• Deviation of tail opposite to the side of touching the skin to right or left of vulva

• Getting tail out of the way

What are the hormone profiles of estrus?

• Estrogen begins to fall

• Progesterone starts to rise: First rise of progesterone is correlated with LH peak**

• Estrogen and Progesterone are necessary for standing behavior in the bitch

• LH and FSH both peak at onset of estrus - May need both for ovulation

What causes the preovulatory rise in progresterone?

the luteinization of follicles during estrus (estrual luteinization)

What estrus cycle phase are these?

left: proestrus

right: estrus

How does vaginal cytology appear during estrus?

• >90% Cornified superficial epithelial cells (squames), lots of anuclear squames (One rule of thumb used to determine estrus is 100% cornified and 50% anuclear)

• No WBC’s - Vaginal wall too thick to cross

• Few RBC’s

• Little or no debris in background of slide

• Sometimes see bacteria

• Cells may clump (“sheeting”) just prior to cytologic diestrus

What phase of the estrous cycle is this?

estrus

What phase of the estrous cycle is this?

estrus

What phase of the estrous cycle is this?

anestrus

What phase of the estrous cycle is this?

diestrus

What phase of the estrous cycle is this?

diestrus

What phase of the estrous cycle is this?

diestrus

What occurs during canine diestrus?

• The female begins to refuse the male - Although she may still be attractive to male dogs

• The uterus develops remarkable tone

• Duration of diestrus is variable: Generally about 60 days (range of 45-90)

• Mammary development in the non-pregnant bitch is subtle

• Mammary development reflects prolactin levels of the bitch

What is seen on vaginal cytology and vaginal speculum exam during diestrus?

Vaginal cytology:

• Superficial cells decrease

• Parabasal and/or small intermediate cells increase

Vaginal speculum:

• Rounding out or smoothing mucosa

• May see variegated red/white areas

What are the changes associated with diestrus?

• Vulvar swelling decreases

• Vulvar discharge disappears: sometimes see scant purulent discharge early (normal)

• Vaginal hyperplasia disappears

• Vaginal cytology: Abrupt change to non-cornified cells, Influx of neutrophils

• Progesterone peaks at 3 weeks

• Prolactin - Luteotropic

What happens during canine anestrus?

• Male shows no sexual interest in the female & Female shows no sexual interest in the male

• Vulva appears normal (not swollen)

• Vaginal cytology few cells and non-cornified: Superficial cells absent, ± neutrophils & bacteria (low numbers)

• Vaginal wall is very thin and appears pale on vaginal speculum

• Progesterone is baseline (<1ng/mL)