Effects of Selenium on Bull’s Sperm Oxidative Stress and Viability Under in Vitro Conditions

The aim of this study was to determine the effects of sodium selenite on the level of oxidative stress and viability of spermatozoa in fresh bull ejaculate in in vitro conditions at different temperatures. Samples of the bull's ejaculates with a concentration of 7 × 105 spermatozoa per ml were placed into the commercial semen extender containing 0 (control), 1 (1Se), 3 (3Se) and 5 (5Se) µg.ml–1 of sodium selenite. The following analyses were performed by flow cytometry after 1, 3, 6, 8, 24, 48 and 72 hours of incubation at 4 °C and 37 °C. All analyses were carried out in triplicate. The level of oxidative stress at both temperatures were significantly lower in the experimental groups in comparison to the control group. However, a significant decline of live sperm concentration and a rise of damaged sperm concentration were recorded, especially in groups 1Se and 3Se in comparison to the control group. Only in group 5Se was there observed a positive effect on the damaged spermatozoa level in comparison with groups C, 1Se and 3Se at 4 °C. In conclusion, the applied concentrations of sodium selenite had a positive effect on the level of oxidative stress in all experimental groups, but mainly at concentration of 5 µg.ml–1 of sodium selenite, especially at 4 °C. However, the effect of selenium was not sufficient for improving the sperm viability.

Effect of quality of sperm chromatin structure on in -vitro production of cattle embryos

Bull effect on results of in vitro embryo production has been well documented. The aim of the present study was to find the relationship between quality of bull sperm chromatin and its effect on in vitro embryo production. Bovine in vitro matured oocytes were fertilized in vitro using capacitated spermatozoa (freshly ejaculated or frozen-thawed) of 12 bulls. Semen was simultaneously processed according to the sperm chromatin structure assay (SCSA) method and was analysed by flow cytometry. At least 3 replications of IVP with the same semen sample were done. The percentage of spermatozoa with abnormal chromatin ranged from 0.4% to 23.8%. All bulls used for the experiment were divided into three groups showing minimal (0.82% ± 6.82%), low (1.70% ± 15.82%) and high (18.16% ± 53.59%) percentages of spermatozoa with abnormal chromatin structure. Both cleavage rates and embryo development to the blastocyst stage were correlated significantly with sperm chromatin abnormalities and resulted in 23.1, 17.7 and 12.2% of blastocysts respectively for sperm with minimal, low and high percentages of chromatin abnormalities. The SCSA method may be used as a practical indicator of suitability of bull ejaculate for IVP purposes.

The chemical composition of the pre-sperm fraction of bull ejaculate obtained by electrical stimulation

1. Semen was collected from bulls by means of the electro-ejaculation method developed by Thibault et al. (1948).2. A copious sperm-free fraction of the ejaculate, produced in the early phase of stimulation, was examined for its chemical composition.3. This secretion was found to have a low protein content, but its chloride concentration was higher than in the sperm-containing fractions of the ejaculate. Fructose and citric acid occurred in very low concentrations, and 5-nucleotidase was absent in the pre-sperm secretion. This indicates clearly that the secretion does not originate either in the seminal vesicles or in the ampullar glands; it is probable that it represents a discharge from the urethral glands.4. The effect of the pre-sperm ejaculate fraction upon bull sperm fructolysis and motility was examined; both were unaffected by a considerable excess of this secretion.5. The chemical composition of the pre-sperm secretion makes it unlikely that under physiological conditions it could play a role in the nutrition of the spermatozoa; presumably, its chief function is the clearing of the urethral passage prior to the descent of the semen proper.