The effect of oviductal epithelial cell co-culture during in vitro maturation on sow oocyte morphology, fertilization and embryo development.

In vitro embryo production in the sow is challenged by poor cytoplasmic maturation, low sperm penetration and low normal fertilization, leading to the development of poor quality blastocysts containing a small number of nuclei. In prepubertal gilt oocytes, the presence of porcine oviductal epithelial cells (pOECs) during maturation increases cytoplasmic maturation and blastocyst development. These aspects, as well as blastocyst quality, may be improved when adult sow oocytes are matured with pOEC. Therefore, the effect of the presence of pOEC on sow oocyte morphology, fertilization and the progression of embryo development was evaluated. The pOEC were cultured in M199 for 18h, then cultured in NCSU23 for 4h before the oocytes were added. Oocytes from 2 to 6mm follicles were matured in 500μl NCSU23, with eCG and hCG, for 24h, and then cultured with or without pOEC, in NCSU23 without hormones, for 18h. In vitro fertilization took place in modified Tris-buffered medium, for 6h, and the presumptive zygotes were then cultured for 162h in NCSU23. Morphology of the IVM oocytes was compared to that of immature oocytes and in vivo matured MII oocytes from slaughtered sows in estrus. The in vitro matured oocytes had a greater diameter and a wider perivitelline space than the immature and in vivo matured MII oocytes (P<0.01). Penetration, polyspermy and pronucleus formation did not differ between the pOEC and Control groups, although the total penetration rate was higher for the Control oocytes (26% versus 39%; P<0.01). Fewer blastocysts developed in the pOEC group than in the Control group (19% versus 27%; P<0.01), but blastocyst growth was accelerated, leading to a higher percentage of hatched blastocysts (3% versus 10%; P<0.01). Finally, the average blastocyst cell number was higher in the pOEC group (47 versus 40; P<0.05) and a greater percentage of blastocysts contained a superior number of nuclei. In conclusion, the addition of pOEC during the second half of in vitro maturation resulted in fewer blastocysts formed, but of those blastocysts that did form the quality was improved.