22 Pregnancy and Twinning

To provide an extra progesterone boost and to maintain the pregnancy until the fetal placenta can take over

Why would horses need a secondary or supplemental corpora lutea in pregnancy?

Endometrial cups release equine chorionic gonadotropin (eCG) or Pregnant Mare Serum Gonadotropin (PMSG)

These hormones help to form the secondary corpora/segmental corpora lutea

Secondary and segmental corpora lutea in horses are used to provide an extra progesterone boost in pregnant mares. How are these created?

Days 40-120 of pregnancy

When do the endometrial cups in horses release equine chorionic gonadotropin (eCG) or Pregnant Mare Serum Gonadotropin (PMSG)?

After 90-100 days, no longer dependent on corpora lutea progesterone

Mares are no longer dependent on the corpora lutea (which produces progesterone) at what day in pregnancy?

After day 80

note: you would use this as a pregnancy diagnostic test, NOT to be used as an indicator in early pregnancy

When does estrone sulfate concentration rise in pregnant mares?

11 months = 340 days

How long is equine pregnancy?

Ventral aspect of the horn

Where do you feel on the uterine horns in horses to feel the "pregnancy bulge"?

Fetus is over pelvis and difficult to reach

SO, fetus only palpable up to day 150 (5 mo.)

You will have a more difficult time palpating a mare pregnancy at 5-7 months. Why?

1. days 5-6: embryo enters uterus

2. day 17: fixation of embryo or prostaglandin release

3. day 25: heartbeat detectable

4. day 35-40: implantation and endometrial cup formation, placenta begins to form

5. day 90-100: no longer CL dependent

6. day 100-120: endometrial cups fully regressed

Name the clinically important events in equine pregnancy for the following days:

1. days 5-6

2. day 17

3. day 25

4. day 35-40

5. day 90-100

6. day 100-120

a. days 5-6

There are several clinically important events in equine pregnancy.

During which day does the embryo enter the uterus?

a. days 5-6

b. day 17

c. day 25

d. day 35-40

e. day 90-100

f. day 100-120

b. day 17

There are several clinically important events in equine pregnancy.

During which day is there fixation of the embryo or prostaglandin release?

a. days 5-6

b. day 17

c. day 25

d. day 35-40

e. day 90-100

f. day 100-120

c. day 25

There are several clinically important events in equine pregnancy.

During which day is the heartbeat detectable?

a. days 5-6

b. day 17

c. day 25

d. day 35-40

e. day 90-100

f. day 100-120

d. day 35-40

There are several clinically important events in equine pregnancy.

During which day is there implantation and endometrial cup formation?

a. days 5-6

b. day 17

c. day 25

d. day 35-40

e. day 90-100

f. day 100-120

d. day 35-40

There are several clinically important events in equine pregnancy.

During which day does the placenta begin to form?

a. days 5-6

b. day 17

c. day 25

d. day 35-40

e. day 90-100

f. day 100-120

e. day 90-100

There are several clinically important events in equine pregnancy.

During which day is the pregnancy no longer CL dependent?

a. days 5-6

b. day 17

c. day 25

d. day 35-40

e. day 90-100

f. day 100-120

f. day 100-120

There are several clinically important events in equine pregnancy.

During which day are the endometrial cups fully regressed?

a. days 5-6

b. day 17

c. day 25

d. day 35-40

e. day 90-100

f. day 100-120

Up to about 30 days

note: around 35-40 days the placenta begins to form

It is difficult to abort the equine fetus once the placenta forms. So, up to what day can you use prostaglandin F2alpha alone to abort?

Twinning

Hydrops

Twisted Umbilical cord

Uterine body pregnancy

Trauma

Treatments

Nutrition

Endocrine Dysfunction

Define the most common causes of non-infectious abortions in horses

Monozygotic or dizygotic (there are two different types of dizygotic)

What are the different types of twins that can happen in horses?

One egg, one ovulation (identical twins)

What are monozygotic twins?

1. two eggs, two ovulations (fraternal twins)

2. two eggs, one ovulation

What are the two different types of dizygotic twins?

Monozygotic twins (aka one embryo splits in half)

Which type of twin has identical genomes resulting from the splitting of a fertilized ovum?

Dizygotic = two eggs, two ovulations

Which type of twin has different genomes?

Asynchronous ovulations

What is the most COMMON cause of dizygotic equine twins?

Often iatrogenic from the hormones we use to induce ovulation aka ovulatory drugs

Asynchronous ovulation (which often leads to dizygotic twins), occurs when ovulations are greater than 24 hours apart. Why does this occur?

Twinning

What is the MOST COMMON cause of non-infectious abortion in mares?

Thoroughbreds and Drafts

Which equine breeds are said to have higher incidences of twinning?

b. 6-10 years

Is equine twinning more likely to occur in horses aged:

a. 2-5 years

b. 6-10 years

1. single = 60%

2. losing both = 31%

3. both to term = 9% (but even the most likely outcome here is they're both born dead)

What are the odds of horses:

1. birthing a single foal in twinning

2. losing both pregnancies in twinning

3. carrying both to term in twinning

1. placental insufficiency is often cause of death

2. both fetuses rarely survive

3. mares require birthing assistance

4. surviving foals are weak

5. higher incidence of retained placenta

What makes equine twin pregnancies undesirable?

At 14-16 days post-ovulation

When can you diagnose equine twins via rectal ultrasonography?

PRIOR TO FIXATION (remember this process occurs at 17 days)

You can diagnose equine twins via rectal ultrasound at 14-16 days post-ovulation. What is this before?

Unilateral fixation = when embryos are touching each other, there is reduced nutrient exchange and 85% of these cases undergo natural reduction with each other

Describe this fixation. What issues does it cause?

Bilateral fixation = these eventually weaken due to compromised contact, though natural reduction is almost-nonexistent

Describe this fixation. What issues does it cause?

UNILATERAL

Which occurs in EARLY development of non-functional membrane to membrane contact, where 70% of twinning cases are this type of fixation:

Unilateral or bilateral fixation

BILATERAL

Which occurs in LATE development of non-functional membrane to membrane contact, where 30% of twinning cases are this type of fixation:

Unilateral or bilateral fixation

Unilateral

Which type of fixation commonly results in natural reduction of twins, Unilateral or bilateral fixation

Singleton

Describe this pregnancy

Type A - twins dissimilar in size

Describe this pregnancy

Type B - twins about equal size

Describe this pregnancy

Type C - one twin undergoing mummification

Describe this pregnancy

Type A - twins dissimilar in size

Describe this pregnancy

Type B - twins about equal size

Describe this pregnancy

Type C - one twin undergoing mummification

Describe this pregnancy

Breed all mares and examine for twins regardless if double ovulation is detected. At 14-16 days, can manually reduce

How do you manage equine twins?

Fetal reduction techniques

Manual crushing, pinching, ultrasound assisted crushing, membrane "slip", fetal cranio-cervical dislocation, ultrasound guided intra-cardiac puncture and termination of pregnancy in horses are all ways of doing WHAT?

Day 14

At what day in the equine pregnancy can you attempt manual reduction or crushing of twins?

Bilateral fixation

In which type of twin fixation must you commonly manually reduce twins, Unilateral or bilateral fixation

Manual or ultrasound assisted crushing

What is the easiest mechanism of twin reduction in mares?

Done prior to fixation around day 16

What day must ultrasound assisted embryo crushing be done before?

Trans-vaginal ultrasound guided aspiration

This mechanism of twin reduction is invasive, typically a last ditch effort after 35 days, or at least after fixation

Fetal cranio-cervical dislocation

This is typically done between 60-110 days of gestation, with a 71% success rate, but takes 1-3 weeks for the fetal heartbeat to stop

Ultrasound guided intra-cardiac puncture (with procaine penicillin or potassium chloride)

Pre-treatment of the mares with progesterone, clenbuterol, banamine, and antibiotics is necessary for WHICH twin reduction technique?

Because the mare cannot return to estrus until endometrial cups regress

Why is it important to know endometrial cups regress around 100-120 days of gestation?

Oxytocin

What hormone is IMPORTANT TO GIVE when you are terminating a mares pregnancy?