Buffalo bull spermatozoa are rich in polyunsaturated fatty acids and are prone to lipid peroxidation. We hypothesised that lipid peroxidation in buffalo bull semen will increase with age and will affect the semen quality. The objective was to compare malondialdehyde (MDA) concentration and the quality of fresh and frozen-thawed semen between aged (13.6 ± 1.0 years; n = 3) and young (3.4 ± 0.3 years; n = 3) Nili-Ravi bulls. The concentration of MDA did not differ (p >.05) between aged vs. young bulls in fresh (2.3 ± 0.2 vs. 2.9 ± 0.7 nmol mL⁻¹), frozen-thawed (53.1 ± 2.8 vs. 48.4 ± 2.6 nmol mL⁻¹) semen and seminal plasma (5.71 ± 0.97 vs. 5.19 ± 1.36 nmol mL⁻¹), respectively. In fresh semen, sperm motility and total concentration did not differ (p > .05) between aged and young bulls. The volume of fresh semen increased (p > .05) while sperm viability and DNA integrity decreased (p < .05) in aged vs. young bulls. In frozen-thawed semen, sperm motility, viability and DNA integrity decreased (p < .05) in aged vs. young bulls. In frozen-thawed vs. fresh semen, MDA level increased within young (48.4 ± 2.6 vs. 2.3 ± 0.2 nmol mL⁻¹) and aged bulls (53.1 ± 2.8 vs. 2.9 ± 0.7 nmol mL⁻¹). Conversely, sperm motility and viability decreased (p < .05) within the age groups between fresh and frozen-thawed semen. In conclusion, (1) lipid peroxidation (MDA) does not increase due to age; however, it is negatively associated with semen quality and (2) cryopreservation steps up lipid peroxidation irrespective of age and deteriorates semen quality of Nili-Ravi bulls.

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.