Early Embryonic Death

For all horse breeders, it is important to realize that not every mare will give birth to a live foal. Failure of the pregnancy can occur at any stage starting from the fertilization of the oocyte or egg. The oocyte develops in the fluid- filled

Share
Favorite
Close

No account yet? Register

ADVERTISEMENT

For all horse breeders, it is important to realize that not every mare will give birth to a live foal. Failure of the pregnancy can occur at any stage starting from the fertilization of the oocyte or egg. The oocyte develops in the fluid- filled follicle (Figure One). When it is mature, the oocyte is shed from the follicle into the fallopian tube. This is called ovulation. The fallopian tubes, or oviducts, stretch from the uterus to the ovaries. If the mare has been bred by a stallion or inseminated in the last two or three days, the fallopian tubes should contain sperm (Figure Two). The sperm will burrow into the oocyte and fertilize it to produce the early embryo.


In the mare, fertilization occurs in the fallopian tube and can take place through either natural or artificial insemination. It is a unique event that brings the genetic material of the parents together. It also is a very complex process in terms of both timing and management. Sperm normally live only two or three days in the fallopian tube, so the mare should not be bred too early in estrus or the sperm could be dead before the oocyte arrives in the fallopian tube. You might wonder how the sperm and oocyte ever manage to meet, but statistics show that pregnancy rates average out at 70% by the end of the season.


The fertilized embryo remains in the oviduct for five to six days. After that time, it leaves the oviduct and enters the uterus. The equine oviduct appears to have the unique ability to retain unfertilized ova. This discovery was made as long ago as 1966 and has been confirmed by many subsequent studies. The mechanism remains unclear to this day.


The next stage in the reproductive process is gestation, which begins when the oocyte is fertilized and ends at birth. During that time, the fetus develops and grows to a state where the newborn foal can survive in the outside world. There are hormonal changes during pregnancy; in particular the hormone progesterone continues to be produced

Create a free account with TheHorse.com to view this content.

TheHorse.com is home to thousands of free articles about horse health care. In order to access some of our exclusive free content, you must be signed into TheHorse.com.

Start your free account today!

Already have an account?
and continue reading.

Share

Written by:

Jonathan F. Pycock, BVetMed, PhD, Dipl. ESM, MRCVS, operates Equine Reproductive Services, a first opinion and referral private equine practice based in Yorkshire, England. He has published many papers and book chapters on a variety of equine reproductive topics, and edited the book Equine Reproduction and Stud Medicine. His main interests include ultrasonography, breeding the problem mare, and artificial insemination. Currently, he is evaluating the use of oxytocin and depot oxytocin as a post-breeding treatment for mares.

Related Articles

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from TheHorse.com

Sponsored Content

Weekly Poll

sponsored by:

What lameness issues has your horse experienced? Select all that apply.
267 votes · 534 answers

Readers’ Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form

Create a free account with TheHorse.com!