124 Transfer of in vitro-produced hatched blastocyst as an alternative to increasing pregnancy rate in a commercial cattle farm in the tropics

This field trial was conducted on a cattle commercial farm to increase the pregnancy rate after transfer of in vitro-produced (IVP) embryos. Donor cows were elite pure red Brahman cows and recipient cows were Brahman cross-bred heifers and young cows. Recipients were used after natural or synchronised heat using a commercial progesterone-based protocol. The aims of this study were: (1) to study the effect of transferring two embryos versus one embryo into recipient cows on pregnancy rate; (2) to study the effect of transferring hatched Day 7 blastocysts, either alone or in combination with another embryo, on the resulting pregnancy rate. Good quality cumulus-oocyte complexes (COC) were obtained from donor cows by ovum pickup (OPU) and were matured and fertilised in vitro. Presumptive zygotes were cultured in vitro for six days and the resulting blastocysts were evaluated and classified on Day 7 after in vitro fertilisation. Only embryos described by the IETS (2009) as blastocyst (stage 6), expanded blastocysts (stage 7), and hatched blastocysts (stage 8) were assessed in this study. Pregnancy diagnosis was made around Day 45 after transfer. Data were analysed by logistic regression of SAS. A total of 172 embryo transfers were performed and 78 pregnancies (45.3%) were recorded. Of the 254 embryos transferred either in single (n = 86) or double (n = 86) embryo transfer, 23 were regular blastocysts (stage 6), 186 were expanded blastocysts (stage 7), and 45 were hatched blastocysts (stage 8). Single embryo transfers included blastocysts at stage 7 (n = 61) or 8 (n = 25), which resulted in pregnancy rates of 42.6% (26/61) and 56% (14/25), respectively (P > 0.05). There were no significant differences in pregnancy rates between single (40/86; 46.5%) and double (38/86; 44.2%) embryo transfers. Of the 45 stage 8 blastocysts, 25 were transferred alone or combined with a stage 6 (n = 3) or 7 (n = 17) blastocyst. Of the remaining 169 stage 7 blastocysts, 61 were transferred alone or combined with another stage 7 (n = 92) or stage 6 (n = 16) blastocyst. Eight stage 6 blastocysts were transferred paired. Most reports agree that embryo quality, but not embryo stage of development, is the main determinant of pregnancy rate (Hasler 2001 Theriogenology 56, 1401–1415). However, in the present study, the pregnancy rate in recipients who received at least one stage 8 blastocyst was 48.9% (22/45), whereas for recipients who received at least one stage 6 or 7 blastocyst, the pregnancy rate was 26.1% (6/23) and 45.7% (64/140), respectively. Even though numerical differences were in favour of hatched (stage 8) blastocysts, no statistical differences were detected in this commercial setting, probably due to the need for a greater number of transfers. It is interesting to note in this study that the greatest pregnancy rate corresponded to recipients who received at least one hatched blastocyst (stage 8). Since embryos at this advanced stage of development are not usually transferred, this finding could represent an alternative that deserves further research.

The authors thank Mr Leonardo Atencio, Mrs Maritza Montiel, and Dr Juan Carlos Velarde for their collaboration and invaluable assistance.