Mare Reproduction

Question 1

In which part of the ovary will ovulation ALWAYS occur in the mare?

Answer 1

The ovulation fossa

Question 2

What is the length of the mare’s oestrus cycle?

Answer 2

21-22 days

Question 3

WHat is the timing of ovulation in the mare?

Answer 3

1-2 days before the end of oestrus. A small percentage of mares will ovulate after oestrus.

Question 4

What cyclic seasonal changes do mares go through?

Answer 4

Vernal transition –> Breeding season –> Autumn transition –> Anoestrus

Question 5

Ovulatory follicles in mares range in size from what to what?

Answer 5

35 - 70mm diameter

Question 6

List behavioural characteristics displayed by a mare in estrus:

Answer 6

• Raising tail
• Squatting
• Urinating
• Everting clitoris (winking)

Question 7

WHich hirmone would you test for to determine a mare is in diestrus?

Answer 7

Progesterone

Question 8

What are two methods of artificial lighting to bring forward the onset of estrus?

Answer 8

Constant lighting: 14-16h a day - lights on until 10pm

Intermittent lighting: 1hr of light during the night (10h after onset of dark)

Question 9

What is the aim of treatment with a dopamine antagonist such as domperidone in the lead up to estrus?

Answer 9

To increase prolactin secretion -> increased LH receptors on ovary

Question 10

How many days post-ovulation is the corpus luteum responsive to PGF2-a

Question 11

How can you improve fertility at foal heat?

Answer 11

Delay heat by administering altrenogest from day of foaling for 8 days, then give PGF2-a injection on day 9

OR

Skip foal heat then give PGF2-a 6 days post ovulation to ‘short cycle’ the mare

Question 12

Recommend methods for inducing estrus in anoestrus mares:

Answer 12

• artificial lighting
• dopamine antagonists
• GnRH
• progestins

Question 13

Recommend methods for synchronising estrus:

Answer 13

• Terminate the luteal phase (PGF2-a)
• Lengthen the luteal phase (progesterone)
• Induce ovulation (hcg / deslorelin)
• Inhibit follicular development

Question 14

Recommend methods for inducing ovulation:

Answer 14

*must mimic the LH surge in presence of mature enough follicle (>35mm)

• hCG
• Deslorelin

Question 15

Recommend methods for suppressing estrus:

Answer 15

• Hormonal (progestins - work within 1 day)
• Surgical (ovariectomy - permanent)
• Immunological (GnRH vacc - lasts for 1yr, not recommended if breeding in future)
• Abortion after formation of endometrial cups
• Galss marbles in uterus???

Question 16

What are the advantages of using AI in mares?

Answer 16

• access to a wider rage of stallions
• disease control / reduced contamination
• safety
• prevents overuse of stallion
• more regular semen evaluation

Question 17

What is a major disadvantage of AI in horse?

Answer 17

Thoroughbreds cannot be bred by AI

Question 18

What components are included in semen extendors?

Answer 18

• buffers
• energy
• proteins
• antibiotics

Question 19

What is the goal time period for insemination with frozen semen?

Answer 19

12h before to 6h post ovulation

Question 20

Approximately how long after a hCG / deslorelin injection does ovulation occur?

Answer 20

~36h

Question 21

What advantages does embryo transfer offer?

Answer 21

• Enables breeding at earlier age
• Production of offspring from endangered species
• Pregnancies from mares still in competition
• Potentially >1 foal per mare each year
• Removes risks of foaling in valuable mares

Question 22

When does the reciepient mare need to ovulate for embryo transfer?

Answer 22

Needs to have ovulated 1 day prior or up to 3 days after the donor mare

Question 23

List some ultrasonographic signs of early embryonic loss:

Answer 23

• irregular shape of embryonic vesicle
• prolonged mobility of vessel (>day 16)
• excessive endometrial oedema
• fluid within uterine lumen
• undersized embryo for age
• no heartbeat by day 30 / loss of heartbeat

Question 24

Is hydrops amnion or hydrops allantois more common in mares?

Answer 24

Hydrops allantois

Question 25

How would you treat hydrops of foetal fluid in a mare?

Answer 25

Induction of abortion - foetus usually non-viable. Pre-treat mare with fluid and gradual siphoning of fluid to avoid shock.

Question 26

If a mare has had hydrops, is it likely to reoccur?

Answer 26

Nope

Question 27

What are some complicating sequelae of hydrops?

Answer 27

* rupture of the prepubic tendon / abdominal musculature * uterine rupture * inguinal herniation * abortion * hypovolaemic shock

Question 28

How would you treat ventral abdominal rupture if the goal is to save the mare vs foal?

Answer 28

To save mare: induce parturition To save foal: apply support wraps and nurse mare until parturition can be induced

Question 29

What is the minimum concentration of progesterone required to maintain pregnancy?

Answer 29

4.0ng/mL

Question 30

What should you tell clients about twin pregnancies?

Answer 30

\<15% of twin pregnancies will result in the birth of live twin foals that are likely to survive

Question 31

When an aborted foetus is smaller than expected for gestation length what does this suggest?

Answer 31

A chronic placental disease (mycotic placentitis) causing intra-uterine growth retardation

Question 32

What is the most common cause of sporadic abortion in mares?

Answer 32

*Streptococcus zooepidemicus*

Question 33

A mare starts lactating 2 weeks before she is due to foal and upon rectal palpation her uterus feels thickened. What condition do you suspect?

Answer 33

Placentitis / late pregnancy failure

Question 34

Does TMS cross the placenta?

Answer 34

Yes!

Question 35

After how long is the placenta considered retained?

Answer 35

If itis not expelled within 3hrs of birth

Question 36

How can you treat retained foetal membranes?

Answer 36

dilute oxytocin into 1-2L of saline and infuse IV over 30-60min NSAIDs and systemic antibiotics (TMS) should be given to every mare with retained membranes +/- tetanus prophylaxis

Question 37

What defines persistent mating induced endometritis?

Answer 37

retention of \>2 cm depth of fluid in the uterus \>18 h after breeding