Effect of short-term storage prior to vitrification on pregnancy rates of dromedary camel embryos

Short-term storage of embryos prior to cryopreservation may improve the logistical flexibility of dromedary camel embryo transfer (ET) programs. However, the impact of such storage on embryo cryotolerance remains unclear. The objective of the present study was to evaluate the effect of storing dromedary camel embryos for 24 h at either room temperature (RT) or 4 °C prior to vitrification on subsequent pregnancy rates following ET. A total of 60 Day-7 in vivo-derived embryos were assigned to one of three treatment groups: immediate vitrification without prior storage (NS, n = 20), storage at 4 °C for 24 h prior to vitrification (4C, n = 20), or storage at room temperature (RT, n = 20) for 24 h prior to vitrification. Within each group, embryos were further categorised according to diameter (<500 μm or ≥500 μm). Following warming, embryos were transferred in pairs to synchronized recipients and pregnancy establishment was assessed between days 18-20 and day 60 of gestation. The transfer of NS embryos produced pregnancy rates of 60% (6/10) at 18-20 days and 50% (5/10) at day 60. Transfer of embryos in the 4C group resulted in pregnancy rates of 40% (4/10) and 30% (3/10), respectively. In contrast, embryos stored at RT prior to vitrification failed to establish pregnancies (0/10). These findings demonstrate that while short-term cooling may be compatible with subsequent vitrification, storage at room temperature could severely compromise embryo cryotolerance.