Scientists have made an important development in the field of assisted reproduction in the horse by creating a test tube foal from a vitrified immature oocyte.
The announcement follows the birth of a stallion at the Ghent University Faculty of Veterinary Medicine in Belgium.
The foal has been named VICSI after two crucial techniques that made the birth possible:
- intracytoplasmic sperm injection (ICSI)
Vitrification is a cryopreservation method during which oocytes are cooled very rapidly, resulting in the formation of a glass-like structure and avoiding the formation of ice crystals, which can damage the oocyte.
For ICSI, micromanipulation is used to inject a sperm cell into an oocyte. Oocytes are much more sensitive to low temperatures than embryos.
As reported in Science Daily, cryopreservation of oocytes offers several possibilities in veterinary medicine. Oocytes can be stored and transported for research or for clinical purposes.
In future, it will be possible to store oocytes from a valuable mare, instead of embryos only. This provides more flexibility to the owner with respect to the choice of the stallion.
Up to now, the owner had to decide immediately which stallion was going to be used for fertilisation as the oocytes could not be stored.
The freezing of immature oocytes also provides a number of opportunities for the conservation of genetics of rare or endangered horse breeds or equids, such as zebras.
However, it requires some time to optimise a technique, which has been developed in a scientific research context, to a level allowing practical applications.
In this study, which will be published in the Equine Veterinary Journal, 34% of the vitrified oocytes matured and 5% of the injected oocytes developed to a good embryo.
Using fresh oocytes, the maturation rate is 60% and 20% of the fertilised oocytes develop into an embryo that can be transferred to a mare.