Effect of freezing large numbers of straws of bovine spermatozoa in an automatic freezer on post-thaw motility and acrosomal retention.

Nine ejaculates were extended, placed in .5ml French straws and frozen vertically in two automatic forced vapor freezers (Linde BF-4 and FC-3) at three loads (2,500, 5,000 and full capacity of 7,500 straws in 5-straw goblets on canes). For each load, six locations within each freezing chamber were compared: upper and lower levels of the center, intermediate and corner areas. Semen was extended in skimmilk11% glycerol at 37 C, cooled to 5 C in 3 hr, glycerolated and equilibrated for 4 hr and packaged. Freezing rates were 6 to 10 C/min from +5 to 1 5 C and about 18 C/rain from 1 5 to 1 0 0 C. For combined post-thaw incubation periods of 0 and 3 hr at 37 C, differences in spermatozoal motility and acrosomal retention among the three loads or six locations within or between forced vapor freezers were not significant. Interactions of freezer and location were significant. Acrosomal retention was higher (P<.05) at intermediate locations within the FC-3 than the BF-4; at other locations there was no difference. For comparison, semen from each ejaculate was frozen in static nitrogen vapor in straws held singly (258-straw load) or in 5and lO-straw goblets on canes (240straw load) on horizontal racks. For combined incubation periods, post-thaw survival of sperm did not differ (P>.05) among the two forced vapor and three static vapor systems. In conclusion, when semen is frozen at the rates in this