In vitro production of equine embryos and cloning
The process of producing a genetically identical copy of an original organism is known as animal cloning. The ability to clone an animal by somatic cell nuclear transfer can have huge benefits for disease resistance, conservation biology in endangered species and especially for genetic improvement. Cloning is one of the reproductive biotechnologies used in the equine industry, mainly used in animals of high genetic value. In 2003 the first cloned equid was born.
In Argentina, the technique used is based on the somatic cell nuclear transfer technique, developed by Wilmut et al in 1997. It is shown that during gestation the rates of embryonic loss were very low and 90% of cloned equine pregnancies result in normal birth. Pregnant recipients are monitored by ultrasonography and in cases where pathologies incompatible with life are diagnosed, pregnancy is aborted. Autopsy is performed to allow further research and improvement.
In Brazil a novel procedure for cloning was adapted in 2005 and later used in equine - donor cells in G2 of the cell cycle paired with enucleated oocytes in telophase 2 of meiosis are used. The advantage of this technique is that less time is required because only oocytes that can be activated are used. Cloning rates, however, have been far lower than in other companies.
When it comes to intracytoplasmic sperm injection (ICSI), interactions sperm/oocyte can be overcome as with this technique a selected sperm is injected into a mature mammalian oocyte. This technique is performed using two needles, one to hold the mature oocyte in place and another to inject a sperm directly into the cytoplasm of the oocyte. The pregnancy rates are calculated to be between 70-80%.
Somatic cell nuclear transfer in equine is now a popular option and there are more than 200 equine clones worldwide. Nuclear transfer in horses can have a variety of benefits, especially in situations where the animal is no longer reproductively sound or when it comes to endangered species. With more breeders being interested on how this technique can benefit their breeding programms, somatic sell nuclear transfer will continue to grow and make further developments, however further research is needed.
> From: Maserati et al., JEVS 41 (2016) 42-50. All rights reserved to 2016 Elsevier Inc.. Click here for the online summary.