51 STRESS PRECONDITIONING OF SPERMATOZOA WITH SUBLETHAL CONCENTRATIONS OF ETHANOL IMPROVE POST-THAW SPERM QUALITY IN BULL

Abstract

A variety of controlled mild stressors have been applied for activation of temporary response in oocytes, embryos, and somatic cells. So far, several stressors have been used to induce mild stress, including that of hydrostatic pressure, osmotic stress, mechanical stress, and oxidative challenges. Based on these evidences, we hypothesised that the ethanol in sublethal concentration would be capable of generating mild stress that may ultimately leads to an adaptive response in spermatozoa. To evaluate this hypothesis, semen samples (n = 24, 6 ejaculates/bull) from 4 Holstein bulls were collected and pooled for each replicate. Pooled samples were divided into 5 equal parts and each part diluted with tris-glycerol-based (Optidyl®) extender containing 0 (O-E0), 0.03 (O-E3), 0.09 (O-E9), and 0.15 (O-E15) % (vol/vol) ethanol and frozen. After thawing, sperm motility and velocity parameters (sperm class analysis), apoptosis status (Phospatidylserin Translocation Detection commercial kit), plasma membrane integrity (eosin-Nigrosin staining), malondialdehyde concentration (thiobarbituric acid reaction), and mitochondrial activity (rhodamine-123 and propidium iodide) were evaluated. The data were analysed using Proc Mixed of SAS 9.1 (version 9.1; SAS Institute Inc., 2002, Cary, NC, USA). Tukey's test was used to compare least squares means. As a result, the O-E9 group showed higher (85.2%) percentage of total motility compared with O-E0 (73.6%), O-E3 (51.9%), and O-E15 (67.5%) groups (P < 0.05). A highest (P < 0.05) percentage of live spermatozoa were observed in the O-E9 (62.9%) group as compared with O-E0 (49.4%), O-E3 (50.3%), and O-E15 (49.6%) groups, and also the proportion of apoptotic spermatozoa in the O-E9 (10.6%) group tended to be lowest as compared with those of O-E0 (15.6%), O-E3 (17.2%), O-E15 (14.1%) groups (P > 0.05). The plasma membrane integrity was higher (P < 0.05) in O-E9 (90.8%) compared with O-E3 (75%) and O-E15 (77.2%) groups; however, the difference was not significant when the O-E9 group was compared with the O-E0 group (83.2%; P > 0.05). Obtained results revealed that malondialdehyde level was lower in O-E3 (1.03%), O-E9 (0.63%), and O-E15 (0.89%) groups compared with the O-E0 (1.94%) group (P < 0.05). Furthermore, the percentage of live spermatozoa with active mitochondria was higher in O-E9 (57.7%) and O-E15 (57.5%) groups compared with O-E0 (49.1%) and O-E3 (38.2%) groups (P < 0.05). These results strongly suggest that supplementation of Optidyl® extender with sublethal concentration of ethanol influences post-thawed bull sperm quality in a dose-dependent manner. However, further studies are needed to empirically determine the effect of supplementation on fertilization and pregnancy outcome.