376 FAILURE OF SPERM DECONDENSATION AFTER INTRACYTOPLASMIC SPERM INJECTION IN SWAMP BUFFALO (BUBALUS BUBALIS)

Intracytoplasmic sperm injection (ICSI) has been intensively used to examine the early events of gamete activation, but few studies have been reported for swamp buffalo. The first objective (Exp. 1) was to compare the developmental competence of oocytes after ICSI using either live or dead frozen-thawed spermatozoa. Matured oocytes were fertilized by ICSI using live (n = 148) or dead (n = 151) spermatozoa, followed by chemical activation using calcium ionophore (A23187) and cyclohexamide (CHX) in SOF medium. In vitro fertilization (n = 149) served as thecontrol. Cleavage rate was recorded on Day 2 and blastocyst formation rate was evaluated on Day 7. The second objective (Exp. 2) was to examine the effects of ICSI and activation regime on the decondensation of buffalo spermatozoa. A total of 148 matured oocytes were subjected to ICSI. The sperm-injected oocytes (n = 87) were then activated using the activation protocol as described in Exp. 1. The ICSI oocytes without activation (n = 61) and sham-injected oocytes with activation (n = 35) were used as controls. Nuclear changes of presumptive zygotes were mor- phologically evaluated for pronuclear formation using 4',6-diamidino-2-phenylindole procedure and epifluorescent microscopy at 18 h post-ICSI. Statistical differences were determined among the groups using chi-square test. In Exp. 1, the results showed that the percentages of cleavage and blastocyst formation rate were 79.7, 77.0, and 41.6% and 33.8, 30.5, and 14.8% in the live sperm, dead sperm, and IVF groups, respectively. Embryo development rates did not significantly differ between ICSI groups; however, these rates were significantly higher than in the IVF group (P < 0.05). In Exp. 2, the pronuclear formation rate was significantly higher in the ICSI with chemical (70.1%) and sham injection with chemical (60.6%) groups than in the ICSI without chemical group (3.2%; P < 0.01). However, most of the presumptive zygotes with pronuclear formation from the ICSI with chemical activation group showed only intact sperm heads instead of the full male pronuclear formation. Our study suggests that the chemical activation directly affected the female pronuclear formation and embryo development but that it was not associated with the male pronuclear formation. It is postulated that ICSI oocytes that developed to cleavage and blastocyst stages underwent parthenogenesis after chemical activation. This work was supported by TRF-MAG (MRG-WII515S056) and CHE-TRF Senior Research Fund (RTA5080010).