48 DEVELOPMENTAL COMPETENCE OF CLONED OR PARTHENOGENETICALLY ACTIVATED PORCINE EMBRYOS: EFFECT OF DIAMETER OF PREPUBERTAL GILT OOCYTES.

One of the primary factors influencing the developmental ability of cloned embryos is the oocyte′s diameter (Hirao et al.1994 J. Reprod. Fertil. 100, 333–339). However, the oocyte donor''s age (i.e. its sexual maturity) is also important to consider, because a high proportion of immature oocytes can be expected (Ikeda and Takahashi 2003 Reprod. Fertil. Dev. 15, 215–221). The present study was to investigate the effect of diameter of oocytes collected from prepubertal gilts weighing 100 to 120kg on the developmental ability of cloned and parthenogenetically activated (PA) embryos. Cumulus–oocyte complexes collected from ovaries of prepubertal gilts were in vitromatured for 42 to 44h as described for sow oocytes (Li et al.2008 Theriog 70, 800–808). After removal of the cumulus cells, the matured oocytes were sorted into 2 groups based on visual inspection: large (L) and small (S) oocytes, whereas non-sorted oocytes were used as control (C). In addition, 1 batch from each of the 3 groups of oocytes had their mean size measured. Subsequently, all 3 groups were used for handmade cloning (HMC; Li et al.2009 Reprod. Domest. Anim. 44, 122–127) or parthenogenetic activation (PA; Kragh et al.2005 Theriogenology 64, 1536–1545). Then a chemical activation with 5μgmL-1cytochalasin B and 10μgmL-1cycloheximide in PZM-3 medium was applied for 4h on both HMC and PA embryos. Finally, the activated embryos were washed and cultured in PZM-3 medium using the WOW system. The embryo development was evaluated by cleavage rate (Day 2), blastocyst rate (Day 6), and total cell number in blastocysts. Data were analysed by ANOVA with single factor in Excel (Microsoft Excel 2007, Redmond, WA, USA). The results showed (Table 1) that by simple visual observation, oocytes could be easily sorted into the following groups: L group (mean diameter 110μm, from 105 to 116μm), S group (mean diameter 101μm, from 93 to 106μm) and C group (mean diameter 107μm, from 93 to 116μm). Cleavage rates and total cell number were similar in the 3 groups. However, the blastocyst rate in L group either for HMC or PA was higher than S group. The data confirm that prepubertal gilt oocytes are useful for cloning and PA, but developmental rates can be increased by selection of large oocytes by simple visual observation. Table 1.Data analysis results [ABSTRACT FROM AUTHOR]