Cryopreservation is a key technology to preserve valuable genetics and maximize genetic gains but current cryopreservation methods for bovine embryos results in lower pregnancy rates due to intracellular ice formation during cooling but more importantly due to the rapid ice growth during warming. Ice formation is minimized at faster cooling rate and higher cryoprotectant concentrations but the efficacy to reduce intracellular ice has not been studied directly. We validated the use of synchrotron X-ray diffraction, which is highly sensitive and quantitative to measure intracellular ice formed at cooling and ice growth during warming. In Aim1, bovine embryos will be cryopreserved at one of 4 cooling rates and the relationship between cooling rates on intracellular ice and postthaw embryo re-expansion will be determined. High concentrations of cryoprotectants can reduce ice formation but is toxic to embryos. Aim2, bovine embryos will be cryopreserved at 4 cryoprotectant concentrations at slow cooling rate or ultrafast cooling rate and intracellular ice and post-thaw embryo survival will be determined to identify the optimal cryoprotectant concentration to maximize embryo survival. In Aim3, the extent to which improved cryopreservation methods can improve pregnancy rates will be determined. Heifers will randomly receive an embryo from one of three groups: unfrozen control, cryopreserved at standard cooling rate, or at new ultrafast cooling rate and pregnancy rates determined by transrectal ultrasound. These experiments will provide unprecedented quantitative information about ice formation in embryos necessary for developing optimized cryopreservation protocols with maximal embryo survival to accelerate genetic gains by facilitating embryo transfer.