Cryopreservation of oocytes/embryos is an important technique for genetic resources; however, the success of vitrification in pig oocytes remained at a relatively lower level due to the high content of lipid droplets (LDs). Considering the positive effect of L-carnitine on the function of LDs, the present study was designed to investigate the effect of the addition of L-carnitine on the vitrification of porcine cumulus cells of complexes (cumulus/oocyte complexes [COCs]). First, COCs were randomly divided into two groups: one group of COCs were commonly in vitro maturation (IVM) for 42-46 hours (nonvitrification [NV]), while another group of COCs were IVM with 10 mM L-carnitine (NVL [nonvitrification with L-carnitine addition in IVM]). In addition, random parts of COCs with L-carnitine addition were vitrified (VL [vitrification with L-carnitine addition in IVM]), while vitrification was performed on COCs without L-carnitine used as control group (V). Results showed that the maturation rate of pig oocytes reduced significantly when the vitrification was performed at 16 hours during IVM (VL vs. NVL, 40.09-2.85 vs. 90.76-1.16; V vs. NV, 34.41-2.55 vs. 89.71-1.33, p < 0.01). With the addition of L-carnitine, intracellular LDs were decreased significantly (p < 0.01). However, no difference was observed on the efficiency of vitrification in pig oocytes (VL vs. V, 40.09-2.85 vs. 34.41-2.55, p > 0.05). In addition, not only the reactive oxygen species (ROS) level in pig oocytes with the L-carnitine addition group reduced significantly (p < 0.01), but also the expression of SOD1 gene was improved (p < 0.05). In conclusion, results demonstrated that although no difference could be observed on pig COC vitrification, the LDs and ROS level in pig oocytes could be modified by the addition of L-carnitine, which might be helpful for further development.

The quality of pre‐implantation embryos could affect developmental efficiency after embryo transfer. However, the assessment of pre‐implantation embryos was unsatisfactory, especially in pig embryos to date. Therefore, this study was designed to investigate available and applicable parameters that indicate developmental potential and quality of porcine pre‐implantation embryos produced by handmade cloning (HMC), and parthenogenetic activation without zona pellucida (PAZF) and with zona pellucida (PAZI). Firstly, a common division behaviour was detected, that is the formation of uneven division with two unequal size blastomeres (UD 2‐cell), especially in HMC embryos; then, the proportion of UD 2‐cell was found to be significantly higher than that of even division with equal size blastomeres (ED 2‐cell) (72.56 ± 4.56 vs. 24.57 ± 1.92). The formation of UD 2‐cell might be due to the spindle migration along the long axis in 1‐cell stage, and the cleavage furrow was not formed in the centre of cytoplasm. In the two sister blastomeres of UD 2‐cell, uneven distribution of organelles (mitochondria and lipid droplet) was observed with lower proportion in the smaller one (p < .05). Although no difference in blastocyst rate was observed between UD and ED 2‐cell embryos, the cell number per blastocyst from UD 2‐cell embryos was lower than that from ED 2‐cell embryos (44.15 ± 2.05 vs. 51.55 ± 1.83). Besides, because of non‐synchronized division of each blastomere, the following three cleavage routes were observed in all HMC/PAZF/PAZI embryos: T1 (2‐cell → 3‐cell → 4‐cell → ≥5‐cell → morula → blastocyst), T2 (2‐cell → 3‐cell → 4‐cell → morula → blastocyst) and T3 (2‐cell → 3‐cell/4‐cell → morula → blastocyst). Therefore, in pig in vitro‐produced embryos, division behaviours of uneven volume of cytoplasm and non‐synchronized cell cycles were observed at the early embryonic developmental stage, which might be another potential factor to evaluate embryonic development.

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