Lecture 1: Pregnancy hormones and twins equine

Why would a lower MHz might be preferred over a higher MHz?

Provides a deeper scan

What type of US prob is preferred for rectal pregnancy scans?

5.0 MHz

What does the secondary CLs provide during pregnancies?

Extra P4 boost

A?

LH

B?

FSH

C?

CG

D?

Relaxin

Where is eCG or PMSG released from?

Endometrial cups

When does eCG or PMSG start to be produced?

~day 40-120

What is the function of eCG or PMSG?

acts like LH to help form secondary CLs

When are horses no longer CL dependent?

~day 100

When does estrone sulfates rise during pregnancy?

~day 80

P4 stays low from mid to late pregnancy, when does it rise again?

Before foaling

What is the size of the embryo at 25-30 days?

Golf ball, hen’s egg

How big is the embryo at 45-50 days?

Softball, grapefruit

How big is the embryo at 35-40 days?

Tennis or baseball

When preg checking what do you have to feel?

The ventral aspect of the uterine horn

How long is the fetus palpable for?

Up to day 150

When is the fetus over the pelvis and may be unreachable for rectal palpation?

5-7 months

16 day US

21 day embryo

What happens at day 5-6?

Embryo enters uterus

What happens at day 16?

Fixation or prostaglandin release

What happens about day 25?

Heartbeat detectable

What happens on day 35-40?

Implantation, endometrial cup formation and placental formation starts

What happens about days 90-100?

No longer CL dependent

What happens at day 100-120?

Endometrial cups regress

Day 18

Days 22

Day 24

Day 26

Day 29

Day 36

Day 40

Day 45

What hormone test can you run on unhandled pregnancy horse?

Estrone sulfate (high=pregnant). More reliable than P4

A?

Uterus

B?

Amniotic cavity

C?

Allantoic cavity

D?

Allantoamnion

E?

Allantochorion

One egg, one ovulation twins. Identical genomes and result from splitting a fertilized ovum.

Monozygotic twins

Why are gestations longer if due in spring time?

She is most fertile in summer and there is a longer daylight length in summer

What causes the “pinching effect”?

During the hatching of the blastocyst the zona pellucida can cause splitting of egg

Two eggs, two ovulation twins

Dizygotic twins

Two eggs, one ovulation twins

Dizygotic twins, rare

How can you tell the difference between a fetus and cyst?

Speculation reflection on embryo before day 20 of pregnancy.

What kind of twins are equine twins?

Dizygotic

Why are most equine twins dizygotic?

Results of asynchronous ovulations within 24 hours. The capsule of equine embryo is through to prevent pinching effect.

Why do ansynchrous ovulations occur more than 24 hours apart?

the hormonal signals that trigger ovulation can vary in timing, potentially due to fluctuations in follicle development, hormonal imbalances, or underlying medical conditions, causing one follicle to mature and release its egg significantly later than the other

A?

Capsule

B?

Trophoblast?

C?

Blastocoele

D?

Inner cell mass

When do twins have to be dealt with by?

In the first 40 days of pregnancy

What causes a higher incidence of twinning in the mare?

• Ovulatory drugs

• Mares who previously twinned

• Thoroughbreds and draft mares

• 6-10 years of age

• Bred within 80 days of foaling

When is the US view half allantoic sack and half yolk sac?

Day 30

What are the possible outcomes of twins?

• Single foal birth (60%)

• Loss of both pregnancies (31%)

• Carry both to term (9%)

How often are both twins born alive?

1.26% of the time

Why are win pregnancies undesirable?

• Placental insufficiency

• Rare that both fetuses survive

• Mares may require more assistance

• Surviving foals are weaker

• Higher incidence of retained placenta

What are you checking for day 14-16?

• Bilateral or unilateral attachement

Why is it harder to freeze horse eggs?

Capsule makes it difficult for freezing all the way through egg

When can transabdominal ultrasound be performed?

After day 80

How effective are natural reduction mechanisms post-fixation?

• Less efficient when ovulations are asynchronous

• Coincident with cessation of embryonic mobility

• Related to orientation of twin vesicles writhing uterine lumen

• Associated with nutrient deprivation of one twin

• Less efficient when twins are bilateral

Why do unilateral fixations have 85% natural reduction?

• Early development of non-functional membrane of membrane contact

• Reduced nutrient exchange from endometrium

Why do you have to wait till 14-16 days to check for twins?

Because the second embryo may be too small to see before day 14.

Why does bilateral fixation often have lower natural reduction?

• Late development of non-functional membrane

• Both embryos grow

• Eventual weakening of one or both due to compromised contact

Type A placentation

Type B placentation

Type C placentation

Breeding strategies for management of twins

• Breed all mares

• Examine for twins regardless if double ovulation detected

• If unilateral wait for natural reduction

• If bilateral then manually reduce before d18

What is the most common method to reduce a twin?

Crushing a twin

Should you worry about multiple follicles on an ovary?

No! Go ahead and breed, can deal with twins later

When does crushing have decreased success?

After day 19

What can you give prior to crushing twins?

• NSAIDs

• pretreat with P4

When is aspiration performed?

After fixation (d20-40)

What is the success of aspiration?

~40%

What approach is needed for fetal cranio-cervical dislocation?

Flank laparotomy

When is fetal cranio-cervical dislocation performed?

d60-110.

What is thoracic compression?

Done between d55 to d65. Compress fetus against pelvis using US for extended period to compress heart. Should see heart slow dow.

When is a fetal cardiac puncture performed?

150 days

What pre-treatment is needed for fetal cardiac puncture?

• P4

• Flunixin meglumine

• Clenbuterol

• Antibiotics (TMS)

Intra-cardiac infusion of procaine penicillin.

Fetal cardiac puncture

What is the most common way to terminate pregnancy before day 35?

Prostaglandins

1. What is the primary function of equine chorionic gonadotropin (eCG) during pregnancy?
a. To stimulate milk production
b. To maintain the primary corpus luteum
c. To aid in the formation of secondary corpora lutea
d. To initiate parturition

c. To aid in the formation of secondary corpora lutea

2. At approximately what day of gestation do endometrial cups form in mares?
a. Day 20-25
b. Day 35-40
c. Day 60-65
d. Day 80-85

b. Day 35-40

3. When does a mare's pregnancy typically become corpus luteum independent?
a. Around day 50
b. Around day 100
c. Around day 150
d. Around day 200

b. Around day 100

4. Which hormone can be used as a diagnostic indicator of pregnancy after approximately day 80?
a. Progesterone
b. Testosterone
c. Estrone sulfate
d. Follicle-stimulating hormone

c. Estrone sulfate

5. What is the average gestation length for a mare?
a. 280 days
b. 310 days
c. 343 days
d. 365 days

c. 343 days

6. At what stage of gestation can the fetal heartbeat typically be detected via ultrasound?
a. Day 16
b. Day 25
c. Day 35
d. Day 45

b. Day 25

7. Which of the following is NOT a clinically important event in equine pregnancy?
a. Fixation at day 16
b. Embryo entering the uterus at day 5-6
c. Implantation at day 35-40
d. Fetal movement detection at day 10

d. Fetal movement detection at day 10

8. What percentage of equine twins are typically dizygotic?
a. Less than 50%
b. Approximately 75%
c. Greater than 95%
d. 100%

c. Greater than 95%

9. Which breed of horse has the highest incidence of twinning?
a. Arabian
b. Quarter Horse
c. Thoroughbred
d. Pony breeds

c. Thoroughbred

10. What is the most common outcome of twin pregnancies in mares?
a. Birth of two healthy foals
b. Birth of a single foal
c. Loss of both pregnancies
d. One live foal and one stillborn

b. Birth of a single foal

11. When is the optimal time to perform the first pregnancy exam for twins via ultrasonography?
a. Day 5-6 post-ovulation
b. Day 14-16 post-ovulation
c. Day 25-30 post-ovulation
d. Day 40-45 post-ovulation

b. Day 14-16 post-ovulation

12. Which type of twin fixation has the highest chance of natural reduction?
a. Bilateral fixation
b. Unilateral fixation
c. Monozygotic fixation
d. There is no difference in reduction rates

b. Unilateral fixation

13. What is the most common method used to reduce a twin pregnancy in mares?
a. Fetal aspiration
b. Crushing a twin
c. Fetal cranio-cervical dislocation
d. Thoracic compression

b. Crushing a twin

14. Up to what day of gestation is crushing a twin considered to have a high success rate?
a. Day 14
b. Day 19
c. Day 25
d. Day 30

b. Day 19

15. Which of the following is NOT a factor to consider when deciding how to manage twins in a mare?
a. Stage of gestation
b. Time of season
c. Mare's coat color
d. Subsequent fertility of mare

c. Mare's coat color

16. What is the approximate success rate of twin reduction by aspiration?
a. 20%
b. 40%
c. 60%
d. 80%

b. 40%