Four foals have been born in Europe from frozen embryos that were selected on the basis of sex, it has been announced.
The French public agronomic research institute, INRA, said the births from the transfer of genotyped and cryopreserved embryos were a first for Europe.
It said the goal of the work was to better understand embryonic development, control livestock reproduction, and maintain genetic diversity within breeds.
They said that, with genotyping, the process would enable the horse industry to better determine the traits of a future foal. In this case the embryos were successfully chosen on the basis of sex, but other criteria could potentially be used.
The work was carried out at the INRA’s Val de Loire Centre at Nouzilly, where the technology to maintain embryo viability after genetic testing and cryopreservation was honed.
Last northern summer, the transfer of several embryos took place at the Haras du Pin Stud Farm of the French Institute for Horses and Riding (IFCE) in Orne, which resulted in the birth of four healthy foals.
Seven days after fertilization, embryos were collected from Welsh B ponies owned by the INRA.
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 at -196 degrees.
They were then transferred into saddlebred mares at the Haras du Pin centre.
After an 11-month gestation period, the foals were born in May. They were of the expected sex: two females and two males.
The INRE said it was first time the technique has successfully been used on horses in Europe, and was the product of more than 10 years of various types of embryonic research carried out by INRA and IFCE scientists.
Although embryo preservation techniques are already well developed for cattle, small ruminant species, and even humans, preserving horse embryos was, by comparison, a very complex process.
For instance, horse embryos varied greatly in size: Seven-day-old embryos ranged in diameter from 200 to 700 micrometers. It is very difficult to cryopreserve the largest embryos 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.
The researchers said the success of the process in horses was important on several levels. It had the potential to allow the maintenance of breed genetic diversity, particularly among breeds with small population sizes, such as the Landais or the Poitevin Mulassier.
The factor that currently limits the use of embryo transfer is its cost: the transfer centre must maintain a herd of recipient mares that are reproductively synchronized with the donor mares.
The freezing of the embryos means that the transfer does not have to take place immediately; it can wait until a recipient mare becomes available to receive the embryo.
Finally, it may now be possible to directly repopulate horse herds that have experienced losses as a result of various issues, such as disease-related problems, instead of having to use the indirect technique of crossbreeding.
The researchers said genotyping allowed them to choose embryos based on different criteria, such as sex, the absence of known genetic disorders, or, perhaps in the future, other traits that are tied to behaviour.
They said it was advantageous for the horse industry to be able to determine the traits of a future foal.
“We will next aim to simplify the process to make this technology more accessible and user friendly for those in the horse industry,” a spokesman said.