Embryo Biopsies for Genomic Selection
Embryo genomic selection (preimplantation genetic screening) is increasingly being used to select the best embryos within cattle breeding programs. The procedure starts with the collection of a few cells (biopsy) from each of the embryos before they are individually cryopreserved. The biopsy samples are then genotyped, and the genomic estimated breeding value for each embryo is calculated from prediction equations. These are based on algorithms developed from large reference populations of previously genotyped and phenotyped animals. Based on the genomic estimated breeding value, a decision is made whether to thaw and transfer the embryo or not. Due to the recent availability of low-density bovine single-nucleotide polymorphism (SNP) microarrays, this method is now cost effective. The data in this review describe field results and show that the breeding values calculated from the embryo biopsies are reliable enough for selection. Importantly, the embryo manipulation associated with the procedure only has a very limited negative effect on the resulting pregnancy rate. The method can also be used to prevent the transfer of embryos that are carriers of known recessive lethal genetic defects or other chromosomal aberrations. Therefore it can be concluded that embryo genomic selection can be used in breeding programs to accelerate the rate of genetic gain compared to animal-based genomic selection due to an increased selection intensity among full- and half-sib embryos. Although this review only describes results in dairy cattle, embryo genomic selection can also be used in beef cattle and other livestock species where accurate genomic prediction equations exist.
KeywordsEmbryo Biopsy Genotyping Bovine Genomic selection Preimplantation genetic screening Animal breeding Genetic gain
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