title: In vitro characteristics of frozen-thawed, sex-sorted bull sperm after refreezing or incubation at 15 or 37 degrees C.
abstract: The objective was to determine the in vitro characteristics of frozen-thawed dairy bull sperm after sex-sorting and refreezing and thawing (0, 2, and 4h post-thaw; 37 degrees C) or post-sort incubation at 15 or 37 degrees C for 30 and 24h, respectively. These sperm were compared with nonsorted frozen-thawed sperm (control) and with nonsorted sperm undergoing two cryopreservation procedures (FF; 0, 2, and 4h). Frozen-thawed sex-sorted (FS) sperm maintained at 15 or 37 degrees C had higher (P<0.001) progressive motility (PM), velocity, mitochondrial function, viability, and acrosome integrity than that of control sperm but similar total motility at 0 and 2h of incubation. Frozen-thawed sex-sorted sperm incubated at 15 degrees C maintained high levels of motility (66.5+/-1.6%) and viability/acrosome integrity (64.9+/-1.2%) at 24h incubation and, after rewarming and further 6h incubation at 37 degrees C, acceptable levels of motility (35.8+/-1.6%) and viability/acrosome integrity (51.2+/-1.2%) were maintained. Frozen-thawed sex-sorted sperm maintained at 37 degrees C had lower levels of motility, integrity, mitochondrial respiration, and velocity from 4h of incubation onward than that of those incubated at 15 degrees C. However, when frozen-thawed sex-sorted sperm were refrozen (FSF), motility and velocity were depressed at all hours compared with levels exhibited by control sperm, but membrane viability/acrosome integrity and mitochondrial respiration were similar at 0 and 2h post-thaw. Acrosome integrity of sperm in all groups undergoing sorting was exceptionally high at 0h (> or =90%), even after re-cryopreservation and 4h of incubation (77.5+/-1.3%). Double frozen-thawed nonsorted sperm (FF) had similar motility to FSF sperm at 0 and 2h post-thaw but at all time points had the lowest (P<0.001) levels of acrosome intact/viable sperm and mitochondrial respiration and the lowest velocity at 0 h. In conclusion, whereas sex-sorting improved the functionality of frozen-thawed sperm, refreezing depressed motility, viability, and velocity but not acrosome integrity after extended incubation compared with that of control sperm. Furthermore, frozen-thawed, sex-sorted sperm may be stored for transport at 15 degrees C for up 24h without detrimental effects on in vitro sperm characteristics.
authors.affiliation: Faculty of Veterinary Science, The University of Sydney, NSW 2006, Australia. s.underwood@usyd.edu.au
authors.forename: S L
authors.initials: SL
authors.lastname: Underwood
authors.forename: R
authors.initials: R
authors.lastname: Bathgate
authors.forename: W M C
authors.initials: WM
authors.lastname: Maxwell
authors.forename: G
authors.initials: G
authors.lastname: Evans
mesh_terms: D000177:Acrosome / Q000648:ultrastructure; D000818:Animals; D002417:Cattle; D002469:Cell Separation / Q000379:methods / Q000662:veterinary*; D015925:Cryopreservation / Q000379:methods / Q000662:veterinary*; D008297:Male; D008928:Mitochondria / Q000502:physiology; D012662:Semen Preservation / Q000379:methods / Q000662:veterinary*; D012732:Sex Determination Analysis / Q000662:veterinary*; D013081:Sperm Motility; D013094:Spermatozoa / Q000502:physiology* / Q000648:ultrastructure; D013696:Temperature