Effectiveness of in vitro maturation and in vitro fertilization techniques in pigs

In vitro maturation and in vitro fertilization techniques in pigs have progressed considerably in recent years. Many reports focus on the factors affecting in vitro maturation that lead to normal male pronuclear formation or monospermy after fertilization in vitro. It is suggested that pig follicular fluid (pFF), follicle somatic cells and various hormones are important factors for the maintenance of cytoplasmic maturation of oocytes in vitro, but that fetal calf serum (FCS), which is generally added to maturation medium, is detrimental. A series of experiments clearly indicate that the glutathione (GSH) content of matured oocytes increases greatly when maturation medium is supplemented with cysteine, a precursor of GSH, and the rates of male pronuclear formation increase in parallel with the increasing GSH content. To prevent polyspermy, conditions of maturation and of fertilization in vitro are important. Culture of oocytes in medium with FCS for the first 24 h and with BSA for the second 24 h decreases the incidence of polyspermy, without a significant effect on nuclear maturation. However, it has been shown that secretory macromolecules of the oviduct may reduce the incidence of polyspermy by interacting with fertilizing spermatozoa rather than with oocytes. A reduction of polyspermy by treating spermatozoa with pFF is also reported. In addition to the many improvements in the methodology of in vitro fertilization using unfrozen spermatozoa in pigs, techniques for fertilizing oocytes in vitro with frozen epididymal and ejaculated spermatozoa have also recently been developed.