Equine pregnancy Flashcards
Where is semen deposited by the stallion?
Uterus
Where does fertilisation of the ovum occur?
Ampulla of the oviduct
When does the conceptus enter the uterus (days post-OV)
d5-6 post-OV
What happens to unfertilised ova?
Retained in the oviduct as don’t secrete PGE2 (which relaxes ampullary-isthmic jcn
Timeline of conceptus from fertilisation to implantation
Fertilisation = 12hr post-OV
Entry to uterus = d5-6 post-OV
Mobile conceptus in uterus = d6-d15 (mat recognition of pregnancy)
Fixation = d16 post-OV (at base of uterine horn)
Implantation = d35
Mechanism of maternal recognition of pregnancy in mares
Conceptus is mobile in uterus (d6-15) > contacts every cm of uterus multiple times/day > prevents endometrial release of PGF2a (luteolysin) > maintains CL/high P4 for pregnancy
When/where does fixation of the conceptus occur? Why?
d16/17 at base of uterine horn (jcn w uterine body)
- grows too big to migrate so gets stuck
- implants in either horn (irrespective of side of OV)
What is the nutritional source for the conceptus before & after implantation (d35)?
Before = histiotroph (uterine milk) + yolk sac
After = diffusion of nutrients across placenta
Until what day is loss of the embryo considered EEL? When does it most commonly occur?
EEL = loss before d35 (implantation)
- most often before d11 (before pregnancy dx)
What are some causes (+ eg’s) of EEL in mares?
Intrinsic mare factors = endometritis, endometriosis, P4 deficiency, poor nutrition
Extrinsic mare factors = heat, stress, transport
Embryonic factors = chromosomal abnormalities
What is the role of eCG in equine pregnancy? From what structure is it derived?
eCG = luteotrophic > causes formation of accessory CLs on ovaries > maintains high P4 from d40-120 of pregnancy TF maintains early pregnancy
Source = endometrial cups (discrete raised areas of the placenta which invade the maternal endometrium)
What are the 3 sources of P4 in mares during pregnancy & when are they functional?
Primary CL (≤d180)
Accessory CLs (d40-120)
Placental 5-a-pregnanes (≥d100)
When is the first US pregnancy Dx?
d14 –> follicle-like spherical structure in uterus
When are the routine US pregnancy exams in mares + what do each check?
d14 (post-OV) = conception
d25-28 = viability (hearbeat)
d40 = endometrial cups/amnion formed > stud fee due
d60-70 = foetal sexing
What presumptive signs of pregnancy may be considered?
Served by a stallion
Oestrous periods have stopped (test w teasing)
Change of temperament
Abdo enlargement (>5mo)
Foetal movements
Udder enlargement (last month)
Relaxation of sacro-sciatic lig’s (last 2-3wks)
Why do twins occur (usually)?
Where does fixation of twin conceptuses usually occur?
Double OV (>90%)
- 50% = unilateral double OV (hard to spot on US)
- 50% = bilateral double OV (always check both ovaries)
>70% unilateral implantation
What must be considered in checking for twins at the d14 pregnancy dx exam?
Asynchronous OV (1-4 days)
- size difference ≤ 4mm of conceptuses
- TF smaller conceptus is easily missed (as could be as young as d10 TF undetectable)
What is the cause of abortion in equine twin pregnancies?
Lack of placental area to support both foetuses
- smaller foetus (w less placental area) dies
- drop in 5-a-pregnane causes abortion of both
If born alive, both twins will be weak/runty
Signs of a double OV
Mare displaying signs of oestrus (winking etc.) after 1st OV
If a double OV is confirmed, when should preg dx exam be?
d14 post-OV
- look for 2 concepta
- if concepta are separated > crush one
What actions should be taken in the event of double concepta being visible at the d14 exam (before fixation)?
Crush one of the concepta
- only if concepta are sufficiently separate (may damage both if together)
- once start crushing one, finish the job!
- re-examine at d33-34 (before endometrial cups form) - spontaneous reduction may have occurred
What is spontaneous twin reduction?
When does it occur?
What factor is most important in determining whether it will occur?
Natural loss of one of the twins
B/w d17-40 of gestation
Dependent on location of fixation
- Unilateral fix = >80% spontaneous reduction
- Bilateral fix = very low % spont. red
What management options are available in the event of unilateral twins after fixation?
Manual crush one before d35 (low success rate)
PGF2a (luteolysis) > kill both embryos + start again
Transvaginal US-guided needle aspiration (50% success of one reaching term)
What measures can be taken to ensure twins aren’t missed?
Always scan both ovaries for a dominant follicle
Look for 2 dom follicles on the same ovary
If single OV recorded but 2 CL seen at preg exam (d14), recheck for a 2nd conceptus 2 days later (d16 = d12-14 of 2nd conceptus)
