Abstract
The technical establishment of boar sperm cryopreservation is indispensable for constantly supplying fine spermatozoa to effectively breed rare Okinawa native pig, Agu. Hence, the present study was carried out to determine whether the standing periods of spermatozoa before the onset of cooling procedure had effects on its freezability in association with the resistance to chilling injury, assessed by the integrity of plasmalemma, the acrosomal proteolytic activity, the motile patterns, and the in vitro fertilizing capacity. Ejaculated spermatozoa from four Agu and two Landrace boars were washed by centrifugation within 10 min after collection, suspended in Beltsville thawing solution, and then allowed to stand for 0, 1 or 2 hour at room temperature until dilution with BF5 freezing solution. In Agu, the elongation of standing periods before cooling caused significant (p<0.05) decreases in the integrity of plasmalemma, the proteolytic activity of acrosomal contents, and the rate of motile cells and progressive motility in frozen-thawed spermatozoa. Moreover, the post-thawed spermatozoa without the standing period possessed the highest level of the penetrability to in vitro matured oocytes. However, the influences of the standing periods upon the freezability were not found in Landrace spermatozoa as Agu spermatozoa. Therefore, it is concluded that the freezing method without the standing periods before the onset of cooling procedure is appropriate for cryopreservation of ejaculated spermatozoa in Agu.
