diary of two mares

A Mares Pregnancy

We often think of pregnancy as a delicate and fragile condition. When it comes to horses, this perception is perhaps due to the mare's relatively poor reproductive performance in comparison to other domestic animals. However, in a natural setting, the mare does comparatively well reproductively. Therefore, this seemingly poor performance is due as much to improper management as to any reproductive deficiency. Fortunately, management is something we can control.

The earliest days of an embryo's existence are perhaps the most precarious. During the first 30 days, there is a 10-15% chance that the embryo will be resorbed. Stress, illness, uterine infection, hormonal abnormalities, the presence of twins, and other factors have been implicated in early embryonic loss. Often, the cause remains undetermined.

When the mare conceives, the fertilized egg (zygote) travels down the fallopian tubes and enters the uterus around day 6-7. It migrates throughout the uterus until about day 16 and typically implants into the uterine wall at 6-8 weeks. By day 12-13, the embryonic vesicle is usually large enough to be detected by ultrasonic examinations, during which an image is made by bouncing sound waves off tissues. Ultrasound checks are extremely important at 14 t- 16 day checks. This is the first day you can make sure the mare is no in foal with twins. If possible the vet will pinch off one of the follicles and will check again at day 28 to make sure all is well with the remaining follicle.

Neither teasing, palpation, nor ultrasound has been shown to harm the developing embryo or endanger the pregnancy. However, because of the embryo's uncertain beginning. This is one reason the early checks are so important as it allows you to breed again if she did not settle in foal.


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