Changes in motility, morphology, plasma membrane and acrosome integrity during stages of cryopreservation of buck sperm.

Changes in sperm structure and function occur during the processing of semen. The present study was designed to investigate the effect on buck sperm during different stages of semen preparation including dilution, cooling, equilibration and freeze-thawing. Semen ejaculates from three mature bucks (replicates = 5) were diluted with tris-citric acid egg yolk glycerol extender at 37 ºC, cooled to 4 ºC over 90 min, equilibrated at 4 ºC for 2 h, transferred to 0.5 mL straws, placed in nitrogen vapour, frozen and thawed and then analysed. Sperm samples were assessed for percentage motility, acrosomal and plasma membrane integrity, live sperm, and morphology after dilution, cooling, equilibration and thawing. Mean percentage motility after dilution (86.0 ± 1.4%) was reduced significantly (p < 0.05) due to cooling and equilibration (77.6 ± 1.3% and 74.6 ± 1.4% respectively); furthermore, it decreased significantly (p < 0.05) after freezing and thawing (42.3 ± 2.5%). Mean percentage of live sperm was higher (p < 0.05) after dilution (89.3 ± 1.4%)compared with cooling (84.8 ± 1.8%) and equilibration (80.2 ± 2.5%) and further reduced (p < 0.05) after freezing and thawing (56.0 ± 3.4%). Sperm morphology dropped significantly (p < 0.05) from 96.4 ± 0.3% after dilution to 88.8 ± 1.3% at cooling and further decreased (p < 0.05) after freezing and thawing (81 ± 1.9%). Mean percentage of sperm with normal plasma membrane after dilution (82.2 ± 1.1%) was significantly reduced (p < 0.05) at cooling or equilibration (73.8 ± 1.8) and further decreased (p < 0.05) after freezing and thawing (50.1 ± 2.9%). The percentage of sperm with normal acrosomes did not differ significantly due to dilution, cooling or equilibration (85.8 ± 1.7%, 83.2 ± 1.6%, 81.7 ± 1.8%) but was significantly reduced after freezing and thawing (45.2 ± 2.8%). In conclusion, frozen thawed sperm showed maximum damage to motility, morphology, plasma membrane and acrosome integrity following cooling.