Analysis of different factors influencing the intracytoplasmic sperm injection (ICSI) yield in pigs

Intracytoplasmic sperm injection (ICSI) in pigs is a technique with potential application in diverse fields of animal production and biomedicine. Even though there are some cases of live offspring resulting from this technique, its yield is still quite low compared to other species. The aim of this study was to evaluate different factors affecting the ICSI performance. This was done by studying (1) the sequence of culture media for the oocytes after injection; (2) modifications in the in vitro maturation system (IVM) through meiotic inhibitors such as roscovitine, and changes in the IVM time; (3) oocyte activation through injection of inositol triphosphate (InsP(3)) together with the sperm. In vitro matured oocytes were employed. All the ICSI experiments were performed with fresh ejaculated semen. Results showed that porcine ICSI zygotes give an improved proportion of two-cell embryos using the sequence IVF medium-embryo culture medium (NCSU-23) rather than transferring directly to NCSU-23. Pronuclear formation ability was not affected by prematuration, but a faster embryo development was observed in roscovitine treated oocytes. In relation to IVM times, oocytes matured for 36 h can achieve better fertilization percentages than oocytes matured for 44 h. These results were independent of the roscovitine treatment. Finally, no influence on embryo development was observed until the blastocyst stage with the use of the InsP(3) as an exogenous activating factor.