135 PREGNANCY RATES AFTER SINGLE DIRECT TRANSFER OF BIOPSIED FROZEN–THAWED BOVINE EMBRYOS ACCORDING TO QUALITY

Abstract

In cattle, reliable methods for whole genome amplification (WGA) have been implemented for DNA pre-amplification and subsequent genotyping from embryo biopsy containing 5 cells or more. In France, these methods are now tested under field conditions. Several studies report pregnancy rates after direct transfer of biopsied frozen–thawed grade 1 embryos similar to that intact frozen ones. Even so, grade 2 and 3 embryos represent 25.5% of the transferable embryos (AETE data, 2007) and may limit the use of the above mentioned techniques if results are not satisfactory. The objective of this study was to investigate the impact of the embryo quality on the pregnancy rates after single direct transfer of biopsied frozen–thawed embryos. Embryos were collected on 12 donor cows after 15 sessions of superovulation treatment using FSH injected twice daily in decreasing doses over 4 days. Cows were inseminated at 12 and 24 hours after onset of estrus. Embryos were recovered 7 days post-insemination and evaluated according to IETS standards. Biopsies were performed on stage 4 to 7 grade 1 to 3 embryos using a microblade. Embryonic cells from the biopsy were dry deposited in microtubes and frozen before WGA (QIAGEN REPLI-g^® Mini kit, Valencia, CA, USA) and multi-genotyping (GeneMapper software^® – Applied Biosystems Europe). Each biopsied embryo was equilibrated for 10 min in 1.5 m Ethylene Glycol and then loaded into straw containing two columns of F1 medium separated by a central column of 1.5 m EG with the embryo. The freezing sequence was: –7°C directly; seeding; held for 10 min; 0.5°C min^–1 until –35°C before plunging into liquid nitrogen. Embryos were thawed (straws 10 s in air and 20 s in water at 20°C) and directly transferred into synchronized recipient heifers. Pregnancy was diagnosed by ultrasonography at 35 and 90 days. Effect of embryonic stage and quality on pregnancy rates were analysed by log linear models (Proc CATMOD, SAS Institute Inc). A total of 58 embryos were micromanipulated. All grade 1 and 2 embryos were successfully biopsied and frozen and, 0.8% of grade 3 (2/25) were discarded due to their low quality after biopsy. No significant effect of embryo stage and quality on pregnancy rates was found after direct transfer (Table 1). These preliminary results suggest that high pregnancy rates can be achieved after direct transfer of biopsied frozen–thawed embryos of Grade 1, 2 and 3 allowing most of the embryos to be involved in the genotyping process.

Table 1.  Pregnancy rates following single direct transfer of biopsied frozen–thawed G1 to 3 bovine embryos

This work has been performed through the programme TYPAGENAE (GENANIMAL 4-03) supported by FRT/ANR and Apis-Genes.