4. therio- equine pregnancy and parturition

what is the average gestation length of the mare?

338-343 days

normal gestation can range from 320-412 days

do unfertilized oocytes enter the uterus in mares?

no, unfertilized oocytes do not enter the uterus

unfertilized oocytes stay in the uterine tube until fertilized

how long after ovulation are oocytes viable?

18 hours

how many days after fertilization does the embryonic vesicle enter the uterus?

5.5-6 days after ovulation

growth of the embryo occurs at the same rate regardless of breed up until how many days?

up to 28 days

when does maternal recognition of pregnancy occur in the mare?

day 14-15

what is embryo fixation?

the embryo becomes too large and uterine tone is too great that the embryo mobility ceases

what day does embryo fixation occur?

day 16

if the mare is postpartum, which horn does embryo fixation occur in?

embryo fixation occurs in the base of the non-gravid horn if mare is postpartum

how does pregnancy palpation differ between mares and cows?

unlike the cow, until the fetus is palpable, there are no other cardinal signs besides uterine asymmetry in the mare

when does embryo implantation occur?

day 35-42

what occurs during embryo implantation?

microvillous attachment of the embryo, now considered a fetus

what type of placentation does the mare have?

microcotyledonary epitheliochorial diffuse placentation

when are endometrial cups present?

present from days 35-150 of gestation

what do endometrial cups secrete?

secrete eCG (equine chorionic gonadotropin) from days 35-150

what does eCG do in mares? other species?

eCG in mares has LH like activity, resulting in supplemental CL formation

in other species eCG has FSH-like activity

is evaluating eCG levels in mares a good diagnostic test for detecting pregnancy?

yes and no- it is sensitive, but not specific

if a mare is pregnant and the fetus dies/aborts, the endometrial cups may still persist and secrete eCG (so the test may be positive even when the mare is no longer pregnant)

when are the primary and secondary CLs present during pregnancy in mares?

primary CL: day 5-180

supplemental CL: day 40-180

no CLs present from day 180-term

what stage of pregnancy can eCG useful to confirm pregnancy?

day 35-150

what stage of gestation is estrone sulfate useful to confirm pregnancy?

days 180-220

what is estrone sulfate an indicator of? where does it come from?

comes from the fetal gonad, it is an indicator of fetal well-being

what day of gestation can sexual differentiation begin to be identified ultrasonographically?

days 59-68

what is a premature foal?

foals born under 320 days

what is a dysmature foal?

foals born full-term but have premature characteristics

how often should pre-partum mares be vaccinated during pregnancy for equine herpes virus?

3-4x during pregnancy, at 5,7 and 9 months gestation

what changes in the colostrum occur when the mare is close to foaling out?

1. sodium concentrations decrease

2. potassium concentrations increase

3. calcium concentration increases >250ppm

4. milk pH decreases <6.8

what are the peak hours of parturition for mares?

11pm-4am

what is the 1, 2, 3 rule relating to mare parturition?

foals should be standing within 1 hour, nursing within 2 hours, and the placenta should be passed in 3 hours

where does the mare most commonly retain a piece of placenta?

the missing piece is usually the tip of the non-gravid horn

what is the difference between tetanus anti-toxin and tetanus toxoid?

TAT: serum of horses vaccinated for tetanus (contains anitbodies for immediate protection)

tetanus toxoid: contains modified toxin (creates immunity in 1-2 weeks following vaccination)

when does uterine torsion occur during pregnancy in the mare and cow?

mares: 1-2 months before foaling

cows: usually at term

what should be evaluated via transrectal/transabdominal ultrasound in high risk pregnancies?

fetal heart rate and rhythm (bradycardia results from hypoxia)

uteroplacental thickness (CTUP) for signs of placentitis

what is a red bag delivery?

premature placental separation

Placenta is presented at delivery instead of amniotic sac. Red velvet colour is the chorioallantois. EMERGENCY! Need to cut this layer immediately!

predisposing factors: dystocia, induced parturition, placentitis, placental edema

what are the criteria to induce parturition in mares?

- over 320 days of pregnancy

-relaxation of sacrosciatic ligaments and vulva

-full udder with colostrum filling teats

-cervical dilation

-assessment of fetal maturity (Ca, Na, K)

what are 2 drugs used to induce parturition in mares?

oxytocin and cloprostenol (Estrumate)

what is the mechanism of action of oxytocin to induce parturition?

increases myometrial contractility, 2nd stage completes within 1 hour

what is the mechanism of action of cloprostenol to induce parturition?

completes 2nd stage within 4 hours