Effects of developmental stage, embryonic interferon-tau secretion and recipient synchrony on pregnancy rate after transfer of in vitro produced bovine blastocysts.
Three separate trials of bovine embryo transfers were performed consisting of 32, 41 and 33 transfers, respectively, to examine the effects of (a) the developmental stage of in vitro-derived blastocysts, (b) the amount of interferon-tau (IFN-tau) they secreted during culture and (c) the cyclic stage of the recipient at the time of transfer on the probability of establishment of pregnancy. One blastocyst was transferred into the ipsilateral uterine horn to the CL. At the time of transfer, blastocysts were classified into one of three developmental stages (early blastocyst, blastocyst and expanded blastocyst) and the cyclic stage of each cow was assessed (-12 h, on time, +12 h, +24 h, >24 h). Prior to the second and third trials, blastocysts were individually cultured for 24 h in 50 microl medium droplets and the IFN-tau concentration in the droplet was determined. Logistic regression analyses revealed that expanded blastocysts had a significantly higher likelihood of establishing pregnancy (p = 0.009), and that there was a significant interaction with the cyclic stage of the recipient in this group with lower rates of pregnancy resulting from decreasing synchrony with the recipient (p = 0.033). IFN-tau secretion during culture was significantly higher in expanded blastocysts than in the other two groups (p < 0.05). A significant effect of the pre-transfer level of IFN-tau secretion was found only in the 'Blastocyst' group where transfer of embryos with lower IFN-tau production prior to transfer resulted in higher pregnancy rates (p = 0.047). These results demonstrate that IFN-tau secretion may be a useful tool to predict pregnancy outcome, but only within certain developmental stages.