Exam II: Equine Repro Flashcards
Equine Repro I-IV: Carnevale
Mare Breeding Objectives
Understand the anatomy and reproductive cycle
Be prepared to use these concepts to solve clinical cases
Cyclicity
Seasonally polyestrous: Long daylight
Cycle of 21 to 23 days: 1 week “in” and 2 weeks “out”
Estrus from 5 to 7 days
Receptive:
Stands for stallion, leans, lifts tail, urinates
Diestrus from 14 to 16 days
Not receptive:
Walks away, ignores stallion, swishes tail, ears back, bites or kicks
Mare Breeding Objectives
Predict ovulation based on follicle size and growth
Be prepared to use these concepts to solve clinical cases
Follicles
* Usually, single ovulation
* Increases ~3-5 mm in
diameter per day during
estrus
* ~45 mm diameter before
ovulation
*
Criteria for induction of ovulation
35 mm follicle
Estrus
Uterine edema
Relaxed tone uterus
Open cervix
Estrous behavior
Mare Breeding Objectives
Identify on ultrasound images the follicle, corpus luteum, and uterus during estrus and diestrus
What do ovaries look like on ultrasound during estrus? Diestrus?
What do
Be prepared to use these concepts to solve clinical cases
Uterine Echotexture
Estrus – estrogen causes edema within uterus:
Dark and light pattern
Most pronounced early estrus
Diestrus – progesterone
“Sweatshirt grey”
Follicles
Round
Black (anechoic)
Multiple follicles will be present on ovaries (Growing and regressing)
Dominant (ovulatory) follicle:
Grows 3 to 5 mm per day
Usually, single ovulation
~45 mm diameter
Early Corpus Luteum
Echoic
Moderate to bright grey or white
Easy to image
Can have central, trabeculated area
The CL is considered “mature” at 5 days
Moderate gray
Can have “trabeculated” center
Progesterone
Closed cervix
Toned uterus
No edema
Mare Breeding Objectives
Know when and how to induce ovulation and luteolysis
Be prepared to use these concepts to solve clinical cases
Induction of ovulation
Timing of induction drugs
Too early – will not respond
Too late – can ovulate too early
Criteria for induction of ovulation:
35 mm follicle
Estrus (Uterine edema, Relaxed tone uterus, Open cervix, Estrous behavior
Lysis of the CL (Short cycle)
Time, shorten or synchronize cycles
Mare Breeding Objectives
Understand the basics of seasonality
Be prepared to use these concepts to solve clinical cases
Seasonally polyestrous
Cycles during periods of long daylight
Winter anestrus
Does not cycle
Minimal ovarian activity
Flaccid uterus
More pronounced in colder climates and further from equator
Increase in day length stimulates:
Hypothalmic-pituitary-ovarian axis
Spring (vernal) transition:
2 to 3 months in length
FSH increases prior to LH
Waves of follicular growth (Increasing follicle diameters, No ovulation)
Estrus (Long, variable periods)
Natural breeding season
Varies with location
April to September
Longer as closer to equator
Artificial breeding season
February 15 through July 15
January 1 considered ‘birth date’
Many show/performance breeds
A foal born anytime during the year is considered 1 year old
on January 1 of the following year.
What drugs are used for induction of ovulation?
HCG
Long half life
LH surge vs peak
LH not effective
Acts at follicle
~36 h (1.5 days)
Reduced response with repeated use in same breeding season
SucroMate Equine (GnRH)
Deslorelin acetate
Approved by FDA
Pituitary release of endogenous LH
~40 h (~1.5 days) from administration until ovulation
Luteolysis:
Estrus in 2 to 5 days
Ovulation ~9 days (average)
Varies depending on follicle sizes
If administer with smaller (~20 mm) diestrus follicles, most mares will be ready to breed in ~1 week
Often, ovulation induction in 5 or 6 days
Timing dependent on follicle growth and regression – remember waves
What drugs are used to short cycle a mare?
return to estrus
Short Cycle
Prostaglandin
Will cause lysis of CL
Return to estrus
Shorten cycle about a week
*CL not fully susceptible to luteolytic effects of prostaglandin until 5 days after ovulation
Prostaglandin
Cloprostenol (Estrumate)
Most often used
250 μg, IM
Analogue
Dinoprost (Lutalyse)
5 to 10 mg, IM
Native prostaglandin
More side effects
Side effects:
Short duration
Sweat
Scour
Mild colic
Stallion and Early Pregnancy Objectives
Understand how seasonality affects stallions
Seasonal breeder, like the mare, but no cessation of sperm production
Lower number sperm during short daylight
Important for stallions producing limited sperm or breeding a lot of mares
Reduced GnRH secretion
Lower LH and testosterone
Effect of artificial lighting:
Same concept as mare
Will alter timing of peak sperm
Feb 15 usually start “season”
July end of “season”
Stallion and Early Pregnancy Objectives
Know semen types and how they impact timing of insemination
- Live cover: 2 days
- Fresh AI: 2 days
- Cooled: 1 day
- Frozen: ½ day
Stallion and Early Pregnancy Objectives
Determine best breeding schemes based on your knowledge of semen type and mare management
Criteria to induce ovulation:
35 mm follicle, Endometrial edema, Estrus, Relaxed uterine tone, Open cervix
Induction of ovulation
hCG and/or GnRH analog
~1.5 to 2 days until ovulation
induced ovulation takes +/- 40 hrs. The oocyte remains viable for less than 12 hrs. Therefore:
When fresh semen is deposited into the reproductive tract of the mare, the sperm cells will usually remain viable for at least 48 hours. Therefore, a generally recommended breeding strategy consists of depositing fresh semen into the reproductive tract at least once every 48 hours while the mare is in heat, with at least one dose of semen being deposited within 48 hours prior to ovulation.
Spermatozoa that have been** cooled** for 24 hours will generally remain viable for an additional 24 to 48 hours after deposition into the reproductive tract of the mare. It is therefore recommended that the mare be inseminated with cooled semen within 24 to 48 hours prior to the anticipated ovulation.
If the amount of frozen semen available is not limited, a common breeding strategy is to deposit one dose of frozen semen in the uterus within 12 hours prior to the expected ovulation and deposit a second dose within 6 to 8 hours after ovulation has been detected. Alternatively, if only dose of frozen semen is available, a common strategy is to induce a timed ovulation by administration of a GnRH agonist (i.e. deslorelin or histrelin) at 8:00 pm when the mare is in heat and has a dominant follicle of the appropriate diameter; ovulation would be anticipated 40 hours later (or at approximately 12:00 noon).
Stallion and Early Pregnancy Objectives
Identify early stages of pregnancy based on ultrasound images
Equine Embryo
5-6 days in oviduct
5.5 days, longer old mares and frozen semen
Rapid growth of embryo within uterus
Embryo flush 6 to 8 days
Capsule formation
Motility phase: Embryo rapidly increases in size, round, and changing locations.
Palpation
Detect at 25 to 35 days (on ultrasound can see heart beat at day 25)
Earlier will feel toned uterus and tight cervix
Fail to return to estrus (~16 day)
Ventral bulge at base of uterine horn (fixation)
Careful not to confuse with bladder (60 to 90 days)
Tight cervix
Ovaries pulled central
Later will feel fetus
Intermittent movement
Motility phase: Embryo rapidly increases in size, round, and changing locations.
Management of the Pregnant and Foaling Mare Objectives
Understand the importance of endometrial cup formation and eCG, primary and secondary CLs
Endometrial Cups
Produce eCG (PMSG)
Equine chorionic gonadotropin
Pregnant mare serum gonadotropin
Maintained until programmed cell death
~Days 35 to 120
Individual variation
Regardless of fetal survival after uterine invasion
Prevents rebreed of mare until about 4 months from initial conception if pregnancy lost after cup formation. Failure of normal ovulation.
Management of the Pregnant and Foaling Mare Objectives
Understand hormonal changes associated with pregnancy and treatment options to aid in pregnancy maintenance
Equine Chorionic Gonadotropin
* Use for pregnancy diagnosis
– Blood assay
* Positive test
– Cups are present
* False negative
– Time of sample collection
* False positives
– Fetal death after cup formation
– Note: Most pregnancy losses occur prior to cup formation
Placental Progestins
Placental progestins maintain pregnancy after ~120 days (90 to 150 days)
Minimal ovarian activity
Progesterone Assay:
Not diagnostic
Variable results
Depends on cross reactivity
Estrogen-based Pregnancy Tests
Estrone (E1) and estradiol (E2) produced by the fetal-placental unit
Increase ~ Day 90 of pregnancy
Estrone sulfate (ES):
Initial increase on Day 45 of pregnancy
From ovaries of mares stimulated by eCG
Management of the Pregnant and Foaling Mare Objectives
Be able to identify diagnostic signs of pregnancy loss
low progesterone
going back into estrus
Luteal insufficiency
Uterine inflammation
Uterine fibrosis
Embryo defects
Delayed fertilization
Embryo insult
Infectious/disease/miscellaneous
Return to estrus
May retain CL
Formation of endometrial cups
Palpation or ultrasound
Developmental delay or failure
No or abnormal heartbeat
Disrupted membranes or abnormal appearance
Changes in echogenicity
No foal
Management of the Pregnant and Foaling Mare Objectives
Be able to identify premature placental separation and retained placenta in the foaling mare
placenta considered retained after 3 hours.
Premature Separation of Placenta
‘Red Bag Delivery’
Chorioallantoic membrane fails to rupture, and placenta separates from endometrium
Emergency condition
Loss of blood supply to fetus
