Effect of bulk freezing straws of bovine spermatozoa in a programmed freezer on post - thaw survival.

Twelve ejaculates were extended both in skimmilk and Tris-yolk, packaged in .5-ml French straws and frozen vertically in bulk (10,000 straws/freeze) in a programmed mechanical freezer (Linde CRFC-3). Cooling rates and post-thaw spermatozoal survival in the upper and lower thirds of straws at the following six chamber positions were compared: corner and middle within-goblet positions at center, intermediate and outer chamber locations. Cooling rates generally were faster in the upper third of straws than in the lower third and at the corner rather than the middle within-goblet positions. For combined postthaw incubation periods of 0, 3 and 6 hr at 37 C, motility (photographic and visual) and acrosomal retention (fixed and unfixed samples) were both higher (P greater than .01) for sperm in each extender in the upper third of straws than in the lower third. Spermatozoal motility and acrosomal retention generally were higher (P greater than .05) in each extender at the center rather than at the outer chamber location. Among within-goblet positions, post-thaw survival of sperm was higher (P greater than .05) at the corner than at the middle positions for Tris-yolk but not skimmilk. For comparison semen was frozen in static N vapor in straws held singly (258-straw load) on horizontal racks. For combined incubation periods, post-thaw survival of sperm did not differ (P less than .05) between bulk and static vapor- systems. There also was no difference when each of the six chamber positions was compared individually with static vapor. In conclusion, 33% more straws of semen can be frozen in a mechanical freezer than previously reported, with post-thaw spermatozoal survival comparable to that of sperm in straws frozen conventionally in static vapor.