title: Survival of bull sperm frozen at different rates in media varying in osmolarity.
abstract: The effects of freezing procedures, osmolarity, trehalose, and sucrose on survival of bull sperm in whole milk (WM) and egg yolk-Tris (EYT), semen extenders used worldwide, were studied. Sperm were added to extenders at 25 degreesC, cooled slowly to 5 degreesC, glycerolated, packaged in 0.5-ml straws, and frozen. Different freezing rates were accomplished in two steps. Straws were transferred from +5 degreesC to nitrogen vapor at temperatures ranging from -10 to -100 degreesC in the first step and to liquid nitrogen in the second step. Straws were thawed in water at 35 degreesC. A substantial decrease in sperm motility occurred between -10 and -20 degreesC, as abrupt nucleation occurred following supercooling to -13 degreesC. To study the interactions between osmolarity x cooling rate, WM and EYT extenders were prepared to yield media measuring 220 to 420 mOsm/L. The optimal first-step range of cooling in the two-step procedure was -30 to -70 degreesC, and the highest proportions of motile sperm after freezing and thawing were 61 to 62 in 260 to 300 mOsm/L WM and 63 to 64% in 300 to 340 mOsm/L EYT, equivalent to the results with the control procedure used commercially. As the cooling rate increased (first step to -100 degreesC) sperm motility was much higher in hypertonic than in hypotonic extenders (P < 0.05), indicating the importance of partial dehydration before rapid cooling. Replacing part of EYT and WM with equivalent solutions (same mOsm/L) of sucrose or trehalose had no appreciable effect. These results provide a basis for further investigating simple freezing systems that might be more effective in preserving bull sperm than those currently available.
authors.affiliation: Department of Animal Science, Cornell University, Ithaca, New York, 14853, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: R H
authors.initials: RH
authors.lastname: Foote
authors.forename: C C
authors.initials: CC
authors.lastname: Brockett
mesh_terms: D000818:Animals; D002417:Cattle; D002470:Cell Survival; D015925:Cryopreservation / Q000379:methods*; D005615:Freezing; D005947:Glucose; D005990:Glycerol; D066298:In Vitro Techniques; D008297:Male; D008892:Milk; D009994:Osmolar Concentration; D012662:Semen Preservation / Q000379:methods*; D013081:Sperm Motility; D013094:Spermatozoa / Q000166:cytology / Q000502:physiology; D013395:Sucrose; D013997:Time Factors; D014199:Trehalose; D014325:Tromethamine
chemical_list: C077847:TES-Tris yolk buffer; D014325:Tromethamine; D013395:Sucrose; D014199:Trehalose; D005947:Glucose; D005990:Glycerol