Porcine oocyte preincubation in oviductal fluid flush before fertilization in the presence of oviductal epithelial cells improves monospermic zygote production.

The present study was designed to evaluate the effect of the combination of oviduct fluid flush (OFF) and oviduct epithelial cells (OEC) in modulating the incidence of polyspermy in pigs. Therefore, for in vitro fertilization (IVF), oocyte and sperm were co-cultured in Tris-buffered medium (TBM) either supplemented with 10% OFF (OFFD group), or in the presence of a bovine OEC monolayer (OEC group), or the oocytes were exposed to OFF for 30 min before IVF (OFFB group), or in the presence of an OEC monolayer (OFFB + OEC group). Regardless of sperm concentration used (0.5, 1.5, and 4.5 × 105 cells/ml), supplementation of IVF medium with 10% OFF led to an increased (P < 0.05) monospermy rate, without alteration (P > 0.05) of the penetration rate in comparison with the control and OEC groups. When the IVF medium was supplemented with heparin, an overall increase (P < 0.05) of the final output of the IVF system in terms of zygotes with two pronuclei (2PN) was observed in the OFFD group, compared with the control and OEC groups, at a sperm concentration of 4.5 × 105 cells/ml. At this concentration, OFFB improved the monospermy rate but decreased the penetration rate, resulting in low efficiency of monospermic zygotes production. Despite this, no major effect was observed in the developmental competence of the presumed zygotes up to the blastocyst stage. The combination of OFFB with OEC improved the penetration rate, while maintaining the high monospermic rate induced by OFFB. In conclusion, the combination of treatment of oocytes by diluted OFF 30 min before IVF, followed by IVF in the presence of OEC, improved monospermic zygote production without reducing the penetration rate, when the IVF medium was supplemented with heparin.