Somatic cell nuclear transfer in horses.

The research article discusses the process, challenges, and achievements of equid (a horse species) cloning. This scientific breakthrough, reached only in 2003, was stalled by underdeveloped horse-specific reproductive techniques essential for successful cloning. However, with these techniques developed, scientists began to yield cloned horse offspring and they provided a detailed methodology and current status of this accomplishment.

Technical Procedures for Cloning Equids

The research identifies several key steps in the cloning of equids:

• Competent Oocyte Maturation: The process begins with the maturation of the oocyte, a cell in an ovary which can undergo meiosis to produce an egg cell.
• Oocyte Enucleation and Reconstruction: The nucleus of the matured oocyte is removed (enucleation) and then reconstructed either within a transparent outer layer (zona-enclosed) or outside it (zona-free).
• Efficient Activation: This step ensures high cleavage rates. The process of cleavage involves cytoplasm of the oocyte dividing to form the blastomeres.
• In Vitro Embryo Culture: Lastly, a suitable in vitro (outside of a living organism) embryo culture technique is used.

First Successful Cloning of Equids

The first cloned equid, a mule, was achieved using in vivo-matured (within a living organism) oocytes and instant transfer of the reconstructed embryo (one cell-stage) to the recipient oviduct. The first horse offspring, however, was obtained entirely through in vitro procedures—from oocyte maturation to embryo culture until the blastocyst stage—followed by a non-surgical transfer.

Efficiency and Outcome of Equine Cloning

The text reports that later studies on equine cloning suggest high efficiency compared to other species. So far, cloned equid offsprings seem to be normal and those that have matured to puberty have proven to be fertile.

Potential Benefits of Horse Cloning

The article summarises that horse cloning is now a reproducible technique providing the opportunity to conserve valuable genetics. Specifically, it enables the replication of castrated champions, thus allowing for offspring that would otherwise be impossible to obtain.