Thursday, July 10, 2014

Foals from genotyped frozen embryos

In a European first, scientists at the French Institute of the Horse and Equitation (IFCE) and the French National Institute for Agricultural Research (INRA) have announced the births of four foals from the transfer of genotyped and cryopreserved embryos.

They explain that the goal of this work is to better understand embryonic development, control livestock reproduction, and maintain breed genetic diversity. Furthermore, the researchers claim advantages for the horse industry in being able to determine the traits of a future foal.

The technology to maintain embryo viability following genotyping and cryopreservation was developed at the INRA Loire Valley centre at Nouzilly. Seven days after fertilization, embryos were collected from Welsh ponies from INRA’s resident herd. The embryos were genotyped: scientists sampled some of the embryos’ cells to analyse 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°).

Then last summer, several embryos were transferred into saddlebred mares at the IFCE Haras du Pin centre. The foals were born in May 2014. They were of the expected sex: two females and two males.

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.

Although embryo preservation techniques are already well developed for cattle, small ruminant species, and even humans, preserving horse embryos is a very complex process. For instance, horse embryos vary greatly in size: 7-day-old embryos range 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 scientists say that being able to cryopreserve embryos will allow us to maintain breed genetic diversity, particularly that of breeds with small population sizes. Furthermore, the factor that currently limits the use of embryo transfer is its cost: the transfer centre has to maintain a team of recipient mares that are reproductively synchronized with the donor mares. Cryopreservation 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, 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. 

Why genotype the embryos? The scientists explain that genotyping allows them to choose the embryos they want to use based on different criteria: sex, as in this experiment, the absence of known genetic disorders, or, perhaps in the future, other traits that are tied to behaviour, such as emotivity or sociability. “It is 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.”

For more information (in French):

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