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Effect of Glycerol Equilibration Time and Thawing Rate upon Acrosomal Maintenance and Motility of Bull Spermatozoa Frozen in Plastic Straws^{1, 2,}

The Pennsylvania State University^,5, University Park 16802

Abstract

In a 2 x 4 factorial experiment, 12 ejaculates were diluted in heated skimmilkglycerol, packaged in .3-ml Continental U.S. straws, equilibrated with glycerol for 1/2 or 2 hr, frozen in liquid nitrogen vapor and thawed at four rates (water at 35 C for 15 sec, 55 C for 12 sec, 75 C for 9 sec or 95 C for 7 sec). Thawed samples were incubated at 37 C and evaluated for the percentages of intact acrosomes (presence of apical ridge) and sperm motility at 0, 3, 6 and 9 hr of incubation. Combining all incubation periods, there was a significant (P < .01) increase in the mean percentage of intact acrosomes for each increase in thawing rate (38.1, 47.7, 51.0 and 55.2% for 35, 55, 75 and 95 C);the difference between equilibration times was not significant. Results for sperm motility were similar to those obtained from acrosomal counts. The interaction of equilibration time x thawing rate was significant (P < .01) for intact acrosomes but not significant for sperm motility. Results of regression analyses revealed that for each 20 C rise in thawing temperature, over the range investigated, intact acrosomes increased a mean of 6.6 and 4.4 percentage units while sperm motility increased a mean of 2.4 and 1.6 percentage units at 1/2 and 2 hr of equilibration, respectively. While thawing rate had a greater influence on both acrosomal maintenance and motility than equilibration time, improvement with very rapid thawing (95 C) was greater for sperm equilibrated 1/2 rather than 2 hours.

¹ Authorized for publication on June 10, 1974 as Paper No. 4709 in the Journal Series of The Pennsylvania Agricultural Experiment Station.

² Supported in part by Atlantic Breeders Cooperative, Lancaster, PA. 17601 and Sire Power, Inc. arid NEBA.Tunkhannock, PA. 18657.

³ Present address: Sire Power, Inc., R.D. #2, Tunkhannock, PA 18657.

⁴ The technical assistance of Mrs. A. Keene, Mrs. H. Homan and Mrs. T. Shirk and the supplies provided by Continental Plastics, Inc., Box 336, Darien, WI 53114 are gratefully acknowledged.

⁵ Dairy Breeding Research Center, Department of Dairy Science.