Abstract
Optimization of bovine ovum pick up (OPU) followed by in vitro embryo production (IVP) has been driven by the desire of both beef and dairy cattle breeders to enhance genetic improvement. The work presented in this thesis focuses on optimizing the efficiency and efficacy of the OPU-IVP program. Attention has
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been paid to both genetic and non-genetic factors affecting the outcome of OPU-IVP. Moreover, by performing embryo transfer experiments, it was possible to ensure that effects and resulting conclusions were not limited to the embryo production stage, but also encompassed post-transfer embryo survival and calf characteristics. The optimal maturation culture period for OPU-derived cumulus oocyte complexes (COCs) in relation to their post-fertilization developmental capacity was determined in a retrospective study covering the analyses of OPU, IVP and calving results from commercial program over a 10 year period. In vitro maturation (IVM) culture periods within 16-28 h range had no detrimental effect on embryo production rate, calving rate, birth-weight, gestation length or proportion of male calves. The presence of cysteamine during IVM of OPU-derived COCs significantly increased the embryo production rate (34.4% with cysteamine vs. 23.4% without cysteamine). The improved embryo production was due to an increased percentage of blastocysts, whereas cryotolerance was not affected. This improvement resulted in a mean of 1.73 transferable embryos per OPU session after IVM in the presence of cysteamine compared to 1.06 in the absence of cysteamine. The presence of cysteamine did not affect post-transfer embryo survival or calf characteristics. The presence of an intra-incubator carbon-activated air filtration system (CODA) during in vitro culture (IVC) did not affect embryo production at Day 7 nor embryo stage or quality. However, the pregnancy rate was improved for both fresh (46.3% vs. 41.0%) and frozen/thawed embryos (40.8% vs. 35.6%). Genetic factors influencing the outcome of bovine OPU-IVP and its relation to female fertility were also investigated. For the first time, genetic parameters were estimated for the number of COCs (Ncoc), quality of COCs (Qcoc) and the number and proportion of embryos at Day 4 (NcleavD4, PcleavD4) and Day 7 of culture (NembD7, PembD7 and NTembD7, PTembD7). Estimates of heritability were 0.25 for Ncoc, 0.09 for Qcoc, 0.19 for NcleavD4, 0.21 for NembD7, 0.16 for NTembD7, 0.07 for PcleavD4, 0.12 for PembD7, and 0.10 for PTembD7. Genetic correlation between Ncoc and Qcoc was close to zero, whereas genetic correlations between Ncoc and the number of embryos were positive ranging from moderate to high. These results suggest that COC quality is independent of the total number of COCs collected via OPU and that in general, a higher number of COCs will lead to a higher number of embryos produced. This study identified OPU-IVP traits that could be of potential value for genetic selection. In conclusion, the results presented in this thesis provide a source of useful information for future attempts to improve both the efficiency and efficacy of OPU-IVP programs in commercial breeding enterprises
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