105 BOVINE EMBRYO TYPE, GRADE AND RECIPIENT SYNCHRONY, BUT NOT CORPUS LUTEUM QUALITY, INFLUENCED PREGNANCY RATES IN COMMERCIAL EMBRYO TRANSFER

Abstract

Embryo transfer is a tool that enables progressive cattle producers to reach their reproductive, genetic and financial goals. The complexity of pregnancy establishment increases with any reproductive technology, especially with one with many variables. This clinical analysis employed a statistical model capable of explaining factors that affect pregnancy probability resulting from over 8000 embryo transfers. These data included corpus luteum (CL) quality score, embryo stage (morula to blastocyst) and grade (1–3), recipient synchrony (relative to the embryo age) and pregnancy rate (≥45 days). The CL score was an amalgamation of the palpable diameter of the CL, whether or not a crown was present and the overall quality of the reproductive tract (size of the uterine horns and perceived patency of the cervix). Embryos produced by IVF were transferred fresh and in vivo–produced embryos were transferred fresh (VIVO FRESH) or following cryopreservation (VIVO FROZ). Statistical methods were used to compare types of embryos transferred and pregnancy rates. All data were analysed using JMP 2009 software by logistic regression with the Logit link. Analysis for the odds of pregnancy occurring among groups using contrasts was conducted. Fisher's exact test showed significant differences (P < 0.05) among groups for pregnancy rate, with the VIVO FRESH embryos group having the highest rate (68.5 ± 1.5%) and the VIVO FROZ the lowest (54.7 ± 1.6%) and the IVF embryos were intermediate (62.1 ± 3.3%). Synchrony, stage, embryo grade and CL quality were analysed for their predictive ability of pregnancy rates in the IVF, VIVO FRESH and VIVO FROZ groups using effect tests with a P < 0.05. Interestingly, the CL quality had no predictive ability for any of the groups. Effectors that had an influence on the VIVO FROZ group included synchrony, stage and embryo grade. However, for the IVF and VIVO FRESH groups, pregnancy rates were affected by only embryo grade. Retrospective, observational analysis of commercial embryo transfer data represents a challenge to meaningful interpretation. Because of the nature of the business, experimental treatments cannot always be developed and implemented. Nonetheless, valuable information is gained by using appropriate statistical methods. As anticipated, these data suggested that the type of embryo transferred, grade and synchrony of the recipient are all important factors, particularly for cryopreserved embryos. Unexpectedly, the score of the CL did not influence pregnancy outcome regardless of embryo type. Evaluation of clinical data allows adjustment of embryo transfer protocols, facilitates genetic gain via enhanced reproductive success and provides a unique opportunity to analyse large, real-world data sets.