Four Foals Produced using Genotyped, Cryopreserved Embryos

Scientists from the French National Equestrian School (IFCE) and the French National Institute for Agricultural Research (INRA) have announced that, for the first time in Europe, four foals were successfully born as the result of the transfer of genotyped and cryopreserved embryos.

The goal of this work is to better understand embryonic development, control livestock reproduction, and maintain breed genetic diversity. Furthermore, it could be advantageous for the horse industry to be able to determine the traits of a future foal.

The genotyping and cryopreservation took place at the INRA Val de Loire center at Nouzilly. Then, last summer, the embryo transfer took place at the IFCE Haras du Pin Stud Farm, located in the French department of Orne. The partnership between the two institutions has now been cemented by the birth of the healthy foals.

What were the steps leading up to the birth of these foals?

Seven days after fertilization, researchers collected embryos from Welsh ponies that are part of INRA’s livestock herds. The embryos were genotyped, meaning scientists sampled some of the embryos’ cells to analyze their genomes. In this experiment, embryos were selected based on sex, the idea being to use sex-based selection to test the technique’s feasibility. The embryos were then cryopreserved in liquid nitrogen.

Last summer, they were transferred into saddle horse mares at the Haras du Pin center. After an 11-month gestation period, the foals were born last month. As expected, two females and two males were born.

This is the first time that such an event has taken place in Europe, and it is the product of more than 10 years of various types of embryonic research carried out by INRA and IFCE scientists.

What made it so difficult to apply this technique to horses?

Although embryo preservation techniques are already well developed for bovines, small ruminant species, and even humans, preserving equine embryos is a very complex process. For instance, horse embryos vary greatly in size; for example, 7-day-old embryos range in diameter from 200 to 700 micrometers.

Additionally, it is very difficult to cryopreserve embryos on the larger end of that scale because the liquid inside them forms ice crystals when the embryos are frozen at very cold temperatures. What’s more, horse embryos are surrounded by a capsule that interferes with successful cryopreservation.

Why genotype the embryos?

Genotyping allows veterinarians and breeders to choose the embryos we want to use based on different criteria, such as sex (like in this experiment), the absence of known genetic disorders, or, perhaps in the future, other traits that are tied to behavior, such as emotivity or sociability. It could be advantageous for the horse industry to be able to determine the traits of a future foal. Researchers will next aim to simplify the process to make this technology more accessible and user-friendly.

What is the significance of this event?

There are several reasons why being able to successfully cryopreserve embryos is important. For example, it allows veterinarians and researchers to maintain breed genetic diversity, particularly that of breeds with small population sizes, such as the Landais or the Poitevin Mulassier.

Furthermore, the factor that currently limits the use of embryo transfer is its cost: The transfer center has to maintain a team of recipient mares that are reproductively synchronized with the donor mares. Cryopreservation, however, means that the transfer doesn’t have to take place immediately; it can wait until a recipient mare becomes available to receive the embryo.

Finally, this technology could make it possible to directly repopulate horse herds that have experienced losses instead of having to use the indirect technique of crossbreeding.

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