Equine pregnancy

Question 1

Average gestation in the mare?

Answer 1

336 (can be highly variable)

Question 2

Outline the key events which occur during equine pregnancy

Answer 2

• Fertilisation occurs in ampulla of oviduct
• Day 5-6 embryo enters the uterus
• Embryo migrates around the uterus to day 15-16 - stimulates MRP and prevents PG release
• On day 15-16 embryo fixes in position
• Placental attachment begins at 36 days
• Production and attachment of endometrial cups
• Foetus grows into uterine body after 70-80 days, found mostly in the body until 6-7 months , after which it is so large it occupies part of the horn again.

Question 3

How long do endometrial cups support pregnancy?

What is their role?

Answer 3

From day 35 to five months pregnancy

Release eCG which maintains the primary CL and encourages secondary CLs to form - P4 release

Question 4

From what day is the equine pregnancy maintained by foetal progesterone?

Answer 4

By around day 200 (when endometrial cups and CLs have regressed)

Question 5

Why should attempts to abort foals be done before 35 days of pregnancy?

Answer 5

At this day endometrial cups begin to develop, they are maintained even if the foal dies and maintain progesterone levels in the reproductive tract ceasing cyclicity (probably won’t cycle until next season)

Question 6

Around what day would you tease a mare as a PD tool?

Answer 6

day 14-20 - check with stallion and receptivity

Question 7

What endocrine tests are used for pregnancy diagnosis is horses?

Answer 7

Blood eCG – from days 45-90 (beware, they persist even with foal death)

Oestrone sulphate – days 120 onwards – also indicates foetal viability

Urine sample – Oestrone sulphate in urine after day 150

Faecal samples for oestrone sulphate

Question 8

At what day should you be able to ballot the foal on rectal palpation?

Answer 8

day 120

Question 9

How can you distinguish a uterine cyst from a conceptus on ultrasound exam?

Answer 9

The conceptus is migratory from day 0-16

Question 10

Outline a possible scan routine for PDing a mare.

Answer 10

• First scan 15-16 days post mating – Check for pregnancy or return to oestrus, check for twins – can reduce whilst embryos motile and can be separated
• Second scan day 24-26 - heartbeat visible, chance of embryonic death lessened, still can reduce twins (more difficult), before cups established – can terminate pregnancy
• Third scan 6 weeks (optional) - embryonic death unlikely now

Question 11

Distinguish between early embryonic death, abortion and still birth.

What can cause them?

Answer 11

• Early embryonic death – from fertilisation to day 40
  
  • Foetal abnormalities, breeding on foal heat, uterine fibrosis/ inflammation
• Abortion – from day 40-300
  
  • Herpes - EHV1
• Stillbirth – from day 300 onwards

Question 12

What virus causes late abortion in horses?

Answer 12

EHV1 - 5 months onwards

Oral/ inhalation contamination (foetal membranes)

Vaccinate at 5, 7 and 9 months pregnancy

Question 13

This notifiable disease causes t cell shedding in stallions

Answer 13

Equine Viral arteritis

Stallions and mares (bred 14 days previously) MUST be reported

There is a vaccine BUT seropositive semen would not be USA accepted!

Question 14

Bacterial abortion

Answer 14

E.coli, streps, staphs, Salmonella

Introduced by ascending infection, at breeding or by haematogenous spread

Question 15

Fungal cause of abortion in horses?

Answer 15

RARE

Aspergillus

Question 16

Why do twin pregnancies often result in foetal mortality?

Answer 16

A foal requires around 70% placental attachment to survive, if there are two foals there won’t be enough to support both

Question 17

Embryo reduction

Answer 17

Manual crushing of an embryo as with twin pregnancies

REMEMBER to give NSAIDs afterwards to prevent inflammatory damage to the other conceptus

Question 18

What can cause failure of pregnancy?

Answer 18

Infectious disease

Twin pregnancy

Cord torsion

Systemic illness

Congenital disease

Idiopathic

Question 19

What can be clinical signs associated with abortion?

Answer 19

• None
• Mare often perfectly well in herself.
• If mare off colour – maybe cause of abortion, not due to abortion.
• Vaginal discharge.
• Running milk.
• Colic/foaling signs.

Question 20

What methods could be used to induce abortion before 3 months pregnancy?

After 3 months?

Answer 20

• Before - Prostaglandin injection - abortion 5-8 days afterward. If endometrial cups present – mare will not return to oestrus this breeding season
• After - Euth foal, dislocate neck, repeated prostaglandins

Question 21

How can foaling be induced in the mare?

Answer 21

Inject 10-20iu oxytocin (1-2ml) every 15-20min until delivery starts

REMEMBER to check milk etc beforehand and beware of risk of uterine rupture, dystocia and RFM