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Effect of Freezing Large Numbers of Straws of Bovine Spermatozoa in an Automatic Freezer on Post-Thaw Motility and Acrosomal Retention^{1 ,2,}

The Pennsylvania State University³, University Park 16802

Abstract

Nine ejaculates were extended, placed in .5-ml 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 skimmilk-11% 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 –15 C and about 18 C/min from –15 to –100 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 5- and 10-straw goblets on canes (240-straw 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 experiment, about four times more straws of semen in 5-straw goblets on canes can be frozen successfully in automatic freezers than previously reported.

¹ Authorized for publication as Paper No. 5731, Journal Series, The Pennsylvania Agr. Exp. Sta. on May 3, 1979.

² Partially supported by Atlantic Breeders Cooperative, Lancaster, PA, Northeastern Breeders Association and Sire Power, Inc., Tunkhannock, PA. The technical assistance of Mrs. A. Keene, Mrs. H. Homan, and Mrs. T. Shirk is gratefully acknowledged.

³ Dairy Breeding Research Center, Dept. of Dairy and Animal Science.