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This study investigated the effects of the bull, sperm type (dead, immotile ormotile) and sperm pretreatment (i.e. mechanical (tail-cutting or tail-scoring)or chemical (heparin, heparin + caffeine, calcium ionophore A23187 ordithiothreitol)) on male pronuclear formation after intracytoplasmic sperminjection (ICSI) in cattle. Three experiments were conducted. In Experiment 1,spermatozoa from three bulls (A, B and C) were used for both ICSI andin vitro fertilization (IVF). The results were thatsperm from bull B yielded a higher penetration/male pronuclear formationrate than that of bull C when used for IVF (89.6%v. 25.6%, P<0.01).However, when injected into oocytes by ICSI, sperm from bull C had a highermale pronuclear formation rate than that of bull B (34.6%v. 16.1%, P<0.05). Theeffects of sperm type and mechanical pretreatment were examined in Experiment2. No significant difference was found in the male pronuclear formation ratewhen the three types of sperm were injected into oocytes. Tail-scored spermachieved a higher male pronuclear rate than that of non-mechanically treatedones (38.2% v. 13.2%,P<0.005). In Experiment 3, chemical pretreatmentswere tested and compared. Higher male pronuclear rates, compared with thecontrol, were obtained when sperm were pretreated with heparin +caffeine, calcium ionophore A23187 and dithiothreitol (48.2%,62.5% and 64.5% v. 25.0%,P<0.05, 0.005 and 0.005, respectively). These resultsindicate that (1) there is a bull variation in malepronuclear formation with ICSI, and the male pronuclear rate by ICSI is notcoincident with the results by IVF, (2) immobilizationof a spermatozoon by tail-scoring before ICSI can improve the formation of themale pronucleus, and (3) an appropriate chemicalpretreatment of spermatozoa is necessary to achieve a higher rate of malepronuclear formation. |
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