CSIRO PUBLISHING www.publish.csiro.au/journals/rfd Reproduction, Fertility and Development, 2010, 22, 59–66 Effects of gamete source and culture conditions on the competence of in vitro-produced embryos for post-transfer survival in cattle Peter J. Hansen A,D , Jeremy Block A,B , Barbara Loureiro A , Luciano Bonilla A and Katherine E. M. Hendricks A,C A Department of Animal Sciences, University of Florida, Gainesville, FL 32611-0910, USA. B Ovatech LLC, Gainesville, FL 32605, USA. C Present address: Southwest Florida Research and Education Center, University of Florida, Immokalee, FL 34142, USA. D Corresponding author. Email: hansen@animal.ufl.edu Abstract. One limitation to the use of in vitro-produced embryos in cattle production systems is the fact that pregnancy rates after transfer to recipients are typically lower than when embryos produced in vivo are transferred. Conceptually, the oocyte and spermatozoon from which the embryo is derived could affect competence for post-transfer survival. There are sire differences in embryonic survival after transfer, but there is little evidence that an embryo’s ability to establish pregnancy is determined by sex sorting of spermatozoa by flow cytometry. The role of the source of the oocyte as a determinant of embryonic survival after transfer has not been examined carefully. Conditions for embryo culture after fertilisation can have an impact on the ability of the embryo to establish pregnancy following transfer. Among the specific molecules produced in the reproductive tract of the cow that have been shown to improve competence of in vitro-produced embryos for post-transfer survival are colony-stimulating factor 2, insulin-like growth factor-1 (for recipients exposed to heat stress) and hyaluronan (for less-advanced embryos). There is also a report that embryo competence for post-transfer survival can be improved by inclusion of a carbon-activated air filtration system in the incubator used to culture embryos. Progress in developing culture systems to improve embryonic competence for survival after transfer would be hastened by the development of in vitro assays that accurately predict the potential of an embryo to establish pregnancy after transfer. A group of 52 genes has been identified that are differentially expressed in embryos that developed to term v. embryos that did not establish pregnancy. Perhaps a gene microarray consisting of these genes, alone or in combination with other genes, could be used to screen embryos for competence to establish pregnancy. Additional keywords: assisted reproduction, fertility, in vitro fertilisation. Limitations in the competence of the transferred embryo to develop to term All else being equal, pregnancy rates following transfer of a blastocyst-stage embryo into a recipient female should be higher than those achieved following insemination. This is because embryo transfer bypasses pregnancy failure caused by defects in the oocyte, ovulation, fertilisation and early embryonic devel- opment. Nonetheless, except in cases where fertility is very poor, for example during heat stress (Putney et al. 1989; Ambrose et al. 1999; Al-Katanani et al. 2002a; Rodrigues et al. 2004), preg- nancy rates following embryo transfer are typically no greater than after AI (Rodrigues et al. 2004; Block et al. 2005; Sartori et al. 2006). It can be inferred from these observations that inef- ficiencies in the production, selection and transfer of embryos limit the transferred embryo’s ability to establish and maintain pregnancy. Competence for post-transfer survival can be a special prob- lem for embryos produced in vitro. Pregnancy rates following transfer of a fresh embryo are often lower for cows receiving an in vitro-produced embryo than for cows receiving an embryo produced by superovulation (Farin et al. 1999; Hasler et al. 2003; Xu et al. 2006; Lonergan et al. 2007; Pontes et al. 2009). Moreover, embryos produced in vitro often survive cryopreser- vation very poorly (Ambrose et al. 1999; Enright et al. 2000; Al-Katanani et al. 2002a; Rizos et al. 2002a). The production of embryos in vitro can also be associated with changes in gene expression (Lazzari et al. 2002; Rizos et al. 2002b), imprinting defects (Suzuki et al. 2009) and an array of fetal abnormali- ties, including increased rates of abortion, fetal overgrowth and altered metabolism (Lazzari et al. 2002; Farin et al. 2006). Realisation of the full potential that embryo transfer rep- resents for genetic selection, fertility enhancement and cross- breeding (Hansen and Block 2004) will depend on improvements in the potential of the in vitro-produced embryo to become a healthy calf after transfer to a recipient animal. Much of the research focus to improve in vitro production (IVP) of bovine © IETS 2010 10.1071/RD09212 1031-3613/10/010059