Comparison of pregnancy in cattle when non-vitrified and vitrified in vitro-derived embryos are transferred into recipients Van Huong Do a, b , Sally Catt c , German Amaya d , Madeline Batsiokis d , Simon Walton d , Andrew W. Taylor-Robinson e, * a School of Health, Medical & Applied Sciences, Central Queensland University, Rockhampton, QLD, 4702, Australia b National Key Laboratory of Animal Cell Technology, National Institute of Animal Sciences, Hanoi, Viet Nam c Education Program in Reproduction & Development, Department of Obstetrics & Gynaecology, Monash University, Clayton, VIC, 3168, Australia d Australian Reproductive Technologies, Mt Chalmers, QLD, 4702, Australia e School of Health, Medical & Applied Sciences, Central Queensland University, Brisbane, QLD 4000, Australia article info Article history: Received 10 April 2018 Received in revised form 23 July 2018 Accepted 23 July 2018 Available online 1 August 2018 Keywords: Cattle Cryopreservation Vitrification In vitro-derived embryo Blastocyst Embryo transfer Pregnancy abstract The present study was conducted in cattle to test the null hypothesis that the pregnancy rate of recipient females is similar when in vitro-derived embryos are transferred either fresh (non-vitrified) or after being subjected to vitrification. Cumulus-oocyte complexes, collected twice (6 weeks apart) from 10 donor cows were matured in vitro and inseminated with frozen-thawed sperm from a single proven bull per donor collection. Cleaved embryos were cultured in vitro until day 7 and any resulting blastocysts were graded for stage [early (unexpanded), advanced (expanded, hatching, hatched)] and/or quality and either discarded (poor quality), or, if deemed suitable, transferred fresh or vitrified for later warming and transfer. All blastocysts were transferred singly to oestrus-synchronized cows and pregnancy monitored by transrectal palpation on days 35, 60 and 90. From 20 collections, 818 cumulus-oocyte complexes were aspirated; however, after grading, only 462 (56.5%) were ranked as suitable quality for maturation and insemination. From those 462 complexes inseminated, 363 (78.6%) cleaved during the process and 243 (52.6%) developed to the blastocyst stage with 194 (42.0%) deemed utilizable, of which 85 were vitrified and 109 were transferred fresh. There was a median of 13 (range 0e24) utilizable blastocysts per cow. Of the 109 non-vitrified blastocysts transferred, there were 45 (41.3%) and 41 (37.6%) recipients that were detected to be pregnant on day 35 and day 90, respectively, subsequent to transfer. Thus, an 8.9% abortion rate was observed (4/45). Of the 85 transferred vitrified-warmed blastocysts, 34 were detected to be pregnant (40.0%) on day 35 following transfer, and all pregnancies were maintained at day 90 (0% abortion rate), which was similar to non-vitrified transfers (P > 0.05, Chi-square test). There was no significant difference in pregnancy rate on day 90 in advanced compared to early blastocysts for either the non-vitrified transfers (9/23, 39.1% vs 33/86, 38.3%) or the vitrified transfers (30/72, 41.6% vs 4/13, 30.8%) (P > 0.05 in each case). In summary, these data show that vitrification of in vitro-derived early and advanced blastocysts is a suitable method of cryopreservation of bovine embryos, and, furthermore, that subsequent transfer of all vitrified/warmed blastocysts into recipient females results in pregnancy rates no different to those attained by non-vitrified transfers into recipient females. © 2018 Elsevier Inc. All rights reserved. 1. Introduction The widespread use of animal reproductive technologies is often reliant on the success of gamete and embryo cryopreservation [1], the two main methods of which are slow freezing and vitrification. Slow freezing is the standard technique used for oocyte and embryo cryopreservation of various species [2]. In the cattle industry, the majority of embryos produced when superovulation procedures * Corresponding author. School of Health, Medical & Applied Sciences, Central Queensland University, 160 Ann Street, QLD, 4000, Australia. E-mail addresses: v.do@cqu.edu.au (V.H. Do), sally.catt@monash.edu (S. Catt), german.amaya79@gmail.com (G. Amaya), mbatsiokis@hotmail.com (M. Batsiokis), simon@artivf.com.au (S. Walton), a.taylor-robinson@cqu.edu.au (A.W. Taylor- Robinson). Contents lists available at ScienceDirect Theriogenology journal homepage: www.theriojournal.com https://doi.org/10.1016/j.theriogenology.2018.07.027 0093-691X/© 2018 Elsevier Inc. All rights reserved. Theriogenology 120 (2018) 105e110