Abstract
Approximately one million in vitro produced (IVP) cattle embryos are transferred worldwide each year as a way to improve the rates of genetic gain. The most advanced programmes also apply genomic selection at the embryonic stage by SNP genotyping and the calculation of genomic estimated breeding values (GEBVs). However, a high proportion of cattle embryos fail to establish a pregnancy. Here, we demonstrate that further interrogation of the SNP data collected for GEBVs can effectively remove aneuploid embryos from the pool, improving live births per embryo transfer (ET). Using three preimplantation genetic testing for aneuploidy (PGT-A) approaches, we assessed 1713 cattle blastocysts in a blind, retrospective analysis. Our findings indicate aneuploid embryos have a 5.8% chance of establishing a pregnancy and a 5.0% chance of given rise to a live birth. This compares to 59.6% and 46.7% for euploid embryos (p < 0.0001). PGT-A improved overall pregnancy and live birth rates by 7.5% and 5.8%, respectively (p < 0.0001). More detailed analyses revealed donor, chromosome, stage, grade, and sex-specific rates of error. Notably, we discovered a significantly higher incidence of aneuploidy in XY embryos and, as in humans, detected a preponderance of maternal meiosis I errors. Our data strongly support the use of PGT-A in cattle IVP programmes.
Highlights
After humans, the most studied mammalian species at the preimplantation stage of development (1–7 days post-fertilization) is cattle
The levels of aneuploidy were determined by log R ratio (LRR)/B allele frequency (BAF) plots and Karyomapping which, when combined, discovered a chromosomal abnormality in 14.1% (n = 241/1713)
The data presented strongly support the use of preimplantation genetic testing for aneuploidy (PGT-A) in cattle In vitro production (IVP) where morphological grading of the embryos alone is not necessarily predictive of the embryo’s potential to develop to term
Summary
After humans (and possibly mice), the most studied mammalian species at the preimplantation stage of development (1–7 days post-fertilization) is cattle. In vitro production (IVP: the cattle equivalent of human IVF) techniques are used extensively for breeding purposes in order to shorten generation intervals and facilitate the bio-secure transportation of genetic resources [1]. The high demand for dairy and beef products has spurred the implementation of new approaches in IVP, combining the most recent advances in embryology with genomics and bioinformatics. Around one million IVP cattle embryos are transferred annually, with a growing proportion screened for genomic estimated breeding values (GEBVs) before embryo transfer (ET) [2,3]. The idea of employing a genomic evaluation to estimate breeding values of individual animals is not new [4]. The in-depth characterisation of the bovine genome sequence has accelerated this trend, and has allowed the formulation of accurate models that describe the association between certain genetic markers (often SNPs: single nucleotide polymorphisms) and valuable traits
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