316 GENOMIC EVALUATION OF BOVINE EMBRYOS WITHIN 24 HOURS

Abstract

The aim of this study was to develop a reliable procedure for genomic evaluation of bovine embryos to determine gender, polled status, and hereditary defects within 24 h after collection. German Simmental animals (n = 15) were superovulated (n = 25) using a standard protocol. Embryos were recovered on Day 7 (Day 0 = oestrus). A total of 217 embryos (morula, n = 130; early blastocyst, n = 43; blastocyst, n = 44) were biopsied with a steel blade attached to a micromanipulator. Biopsied cells were immediately transferred into 1 µL TE buffer to a 500 µL reaction tube and embryos were in vitro cultured until genomic results were available. For commonly used molecular genetic methods (e.g. 5′-exonuclease genotyping, PCR or high density genotyping) DNA amounts of 2–200 ng are required. However, the DNA quantity of a single diploid cell amounts to 6 pg only. The embryo biopsies used, usually consists of 10–30 cells, necessitating an artificial amplification of the embryonic genome. Taking all vital measures to avoid external DNA contamination, isothermal whole genome amplification was performed with the REPLI-g Mini Kit (Qiagen, Valencia, CA, USA) using random hexamers and Phi29-Polymerase. Depending on the number of cells, a total DNA amount of 4–7 µg was achieved. Polled status and gender was determined using PCR with subsequent gel-electrophoresis. 5′-exonuclease assays were used to obtain genotypes for the detection of genetic defects. At present, eight, mostly Simmental-specific genetic disorders can be examined: three traits associated with severe growth retardation, dwarfism (DW), Braunvieh-haplotype 2 (BH2) and stunted growth (FH2), the lethal skin disorder zinc deficiency-like syndrome (ZDL), a fertility trait bovine male subfertility (BMS), embryonic death Fleckvieh-haplotype 4 (FH4), a bleeding disorder thrombopathia (TP) and arachnomelia (A), within 24 h. On average, 8.7 embryos were biopsied per embryo recovery, i.e. 93.9% of the total number of transferable embryos. Fourteen embryo samples (6.5%) totally failed during analysis, possibly due to the loss of samples. In successful analyses, gender was undetermined in two embryos; remaining embryos were 52.2% female and 47.8% male. Polled status could be analysed in 92.6% of the embryos. The analyses of embryos for possible inherited genetic disorders (healthy, heterozygote, or homozygote; n = 578) were successful in 90.1%. The transfer of biopsied embryos (n = 30) led to 63.3% pregnancies (Day 42). A validation of the present results has to be done as soon as the produced calves are born, demonstrating the reliability of the procedure.Research was funded by the Bayerische Forschungsstiftung (AZ-1031-12).