Non-surgical deep intrauterine transfer of superfine open pulled straw (SOPS)-vitrified porcine embryos: Evaluation of critical steps of the procedure

Achievements and future perspectives of embryo transfer technology in pigs

“…Moreover, we obtained the first piglets produced by NsDU transfers of OPS‐vitrified, direct warmed blastocysts (Cuello et al., ), although fertility was below expectations. Surprisingly, when we used the SOPS procedure instead of the OPS procedure, we found that the syringe warming method was detrimental for embryo development post‐warming, either in vitro or in vivo (Gomis et al., ). In the direct warming procedure, the tip of the straw is inserted through the small tip of the syringe, which implies managing difficulties and, therefore, an increased time for the contact of the cryopreserved straws (embryos) with the warming medium.…”

“…This might explain the detrimental effects of direct warming on SOPS‐vitrified embryos. Later modifications of the one‐step warming method by using a dish prior to inserting the embryos into the syringe resulted in promising farrowing rates and litter sizes after NsDU‐ET of SOPS‐vitrified morulae and blastocysts (Gomis et al., ; Martinez et al., ).…”

Recent advances toward the practical application of embryo transfer in pigs

“…The use of NsDU-ET, instead of surgical ET, coupled with embryo vitrification will be essential for the widespread application of porcine ET. In our preliminary experiments that combined both technologies, we obtained acceptable farrowing rates (40%-50%) and litter sizes (5-10 piglets) [44,56], but the number of recipients was low. Therefore, more research is required to confirm the efficiency of NsDU transfer of vitrified embryos.…”

“…3) [34]. We also simplified the conventional three-step warming procedure with a direct warming procedure (one-step dilution) [42][43][44], which is ideal for direct NsDU-ET under field conditions.…”

“…First, pregnancy rates and the numbers of viable embryos on Day 25 of gestation are notably increased in recipients transferred with 24 fresh embryos than in those transferred with 12 fresh embryos [50,60]. Second, litter sizes and piglet production efficiency (calculated as the ratio of the number of live-born piglets to the number of embryos transferred to all recipients) are more than twice as high for surgical or nonsurgical transfer of 25 to 35 vitrified embryos [26,44,[61][62][63] than when transferring only 20 vitrified embryos [56,64,65]. Similarly, in our study, an increase from 30 to 40 vitrified embryos per NsDU-ET increased the piglet production efficiency by 2.5-fold.…”