Impregnation breeding dating
Day 26 to 30 – confirms heartbeat and fact that fetus is alive.
Day 45 – elective examination that has no specific reason since endometrial cups should already be formed by this time.
Vaccinations given to the mare at foaling DO NOT PROTECT the foal since the colostrum does not have adequate time to manufacture the correct antibodies.
Ascarid larvae can be passed in the milk so the mare should be dewormed with a product containing ivermectin.
Be mindful of automatic water supplies and ice-covered troughs during the winter months.
Herpesvirus (EHV-1) can cause late-term abortion and mares should be vaccinated for this disease preferably at five, seven, and nine months of gestation.
If the mare aborts her pregnancy around Day 40-45 or after, it is unlikely she can get pregnant again the same breeding season anyway.
Day 60 – elective examination that has no specific reason, but has become more important since the advent of fetal sexing.
If the embryo does not touch all portions of the uterus by day 16 of gestation, the mare will reject the embryo, and begin showing signs of estrus to begin the next “heat” cycle.
The egg is fertilized in the fallopian tubes and does not enter the uterus until it about Day 6 of gestation.
This is important to remember since you can manipulate the uterine environment up until this stage.
If you consistently check mares at Day 14, at some point you will miss a younger twin that is 12 or 13 days old and too small to be visualized. If twins do survive, they are usually weak and/or non-viable.
Regardless of what day of gestation you check for twins, it is much easier to reduce a twin before they become fixed at Day 17 of gestation. This has only been possible since the advent of ultrasound. Fetal sexing is a revolution in the reproductive industry that had been perfected in cattle but only became available in the equine industry approximately 10 years ago.
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All horses should be examined for twins with transrectal ultrasound.